The British Nutrition Foundation is a British registered charity.

History

It was founded in 1967 by Professor Alastair Frazer. In 1973 it held its first annual conference. It is based between Holborn and Chancery Lane tube stations. The BNF educational programme, Food - a fact of life, was launched in 1991.

Aims

According to its entry in the Charity Commission's register, the aims of the British Nutrition Foundation are:

1. to advance the education of the public, and those involved in the training and education of others, in nutrition; and
2. to advance the study of and research into nutrition for the public benefit, and to disseminate and publish the useful results of such research.

Operations

The BNF's team of nutrition scientists conduct academic reviews of published research on issues of diet and public health. They present their reports in the BNF's Nutrition Bulletin, as well as various Task Force reports, intended for both academic and lay dissemination. The BNF also organises educational programs designed to provide accessible information on diet and health for children and young people, aged 3â€"16+ years. The BNF's education website, foodafactoflife.org.uk, provides teaching and learning resources about food and nutrition.

The BNF receives funding for its projects from a variety of sources, including contracts with the European Commission, national government departments and agencies; food producers and manufacturers, retailers and food service companies; grant providing bodies, trusts and other charities.

Criticism

Concerns have been raised about the BNF's close relationship with the food industry. The BNF receives funding from almost every large food manufacturer and distributor in the UK, including Tate and Lyle, Nestle, PepsiCo, McDonalds and Sainsburys.

Furthermore, Paul Hebblethwaite, a member of the BNF board of trustees and its former chairman, has had "a distinguished career in the food industry working for a number of major companies including Cadbury-Schweppes and Chivers-Hartley". He is also chairman of the Biscuit, Cake, Chocolate and Confectionery Trade Association. Many other members of the organisation’s board of trustees and oversight committees are or have been employees of the food industry.

The BNF is open about its intention to shape UK Government policy on food, and this has led to concerns that it is serving as a lobbying group for the food industry which largely funds it. Derek Shrimpton, former director general, has been quoted as saying: "In the period I was there the foundation was solely taken up with defence actions for the industry." He said that the foundation had been constantly engaged in frustrating government committees aiming to recommend reductions in sugars, salt, and fats.

References

External links

• Official website
• Food - a fact of life
• Nutrition Bulletin journal homepage
• British Nutrition Foundation at Spinprofiles.org

Video clips

• British Nutrition Foundation YouTube channel

Menarche (/mᵻˈnÉ'ːrkiː/ mÉ™-NAR-kee; Greek: μήν mÄ"n "month" + ἀρχή arkhÄ" "beginning") is the first menstrual cycle, or first menstrual bleeding, in female humans. From both social an d medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of fertility.

Girls experience menarche at different ages. The timing of menarche is influenced by female biology, as well as genetic and environmental factors, especially nutritional factors. The average age of menarche has declined over the last century, but the magnitude of the decline and the factors responsible remain subjects of contention. The worldwide average age of menarche is very difficult to estimate accurately, and it varies significantly by geographical region, race, ethnicity and other characteristics. Various estimates have placed it at 13. Some estimates suggest that the median age of menarche worldwide is 14, and that there is a later age of onset in Asian populations compared to the West. The average age of menarche is about 12.5 years in the United States, 12.72 in Canada, 12.9 in the UK and 13.06 ± 0.10 years in Iceland. A study of girls in Istanbul, Turkey, found the median age at menarche to be 12.74 years.

Physiology

Puberty

Menarche is the culmination of a series of physiological and anatomic processes of puberty:

• Attainment of a sufficient body mass (typically 17% body fat).
• Disinhibition of the GnRH pulse generator in the arcuate nucleus of the hypothalamus.
• Secretion of estrogen by the ovaries in response to pituitary hormones.
• Over an interval of about 2 to 3 years, estrogen stimulates growth of the uterus (as well as height growth, breast growth, widening of the pelvis, and increased regional adipose tissue).
• Estrogen stimulates growth and vascularity of the endometrium, the lining of the uterus.
• Fluctuations of hormone levels can result in changes of adequacy of blood supply to parts of the endometrium.
• Death of some of the endometrial tissue from these hormone or blood supply fluctuations leads to deciduation, a sloughing of part of the lining with some blood flow from the vagina.

No specific hormonal signal for menarche is known; menarche as a discrete event is thought to be the relatively chance result of the gradual thickening of the endometrium induced by rising but fluctuating pubertal estrogen.

The menstruum, or flow, consists of a combination of fresh and clotted blood with endometrial tissue. The initial flow of menarche is usually brighter than mature menstrual flow. It is often scanty in amount and may be very brief, even a single instance of "spotting." Like other menses, menarche may be accompanied by abdominal cramping.

Relation to fertility

In most girls, menarche does not mean that ovulation has occurred. In postmenarchal girls, about 80% of the cycles were anovulatory in the first year after menarche, 50% in the third and 10% in the sixth year. Regular ovulation is usually indicated by predictable and consistent intervals between menses, predictable and consistent durations of menses, and predictable and consistent patterns of flow (e.g., heaviness or cramping). Continuing ovulation typically requires a body fat content of at least 22%. An anthropological term for this state of potential fertility is nubility.

On the other hand, not every girl follows the typical pattern, and some girls ovulate before the first menstruation. Although unlikely, it is possible for a girl who has engaged in sexual intercourse shortly before her menarche to conceive and become pregnant, which would delay her menarche until after the end of the pregnancy. This goes against the widely held assumption that a woman cannot become pregnant until after menarche. A young age at menarche is not correlated with a young age at first sexual intercourse.

Onset

When menarche occurs, it confirms that the girl has had a gradual estrogen-induced growth of the uterus, especially the endometrium, and that the "outflow tract" from the uterus, through the cervix to the vagina, is open.

In very rare instances, menarche may occur at an unusually early age, preceding thelarche and other signs of puberty. This is termed isolated premature menarche, but other causes of bleeding must be investigated and excluded. Growth is usually normal. Isolated premature menarche is rarely the first manifestation of precocious puberty.

When menarche has failed to occur for more than 3 years after thelarche, or beyond 16 years of age, the delay is referred to as primary amenorrhea.

Timing

Chronic illness

Certain systemic or chronic illness can delay menarche, such as undiagnosed and untreated celiac disease (which often occurs without gastrointestinal symptoms), asthma, diabetes mellitus type 1, cystic fibrosis and inflammatory diseases, among others. In some cases, because biochemical tests are not always discriminatory, underlying pathologies are not identified and the girl is classified as constitutional growth delay. Short stature, delayed growth in height and weight, and/or delayed menarche may be the only clinical manifestations of celiac disease, in absence of any other symptoms.

Effects of stress and social environment

Some of the least understood environmental influences on timing of puberty are social and psychological. Nearly all of the research on these effects has concerned girls, partly because female puberty requires greater physiological resources and partly because menarche involves a clear threshold event that makes survey research into female puberty much simpler than male. In most of these studies menarche was specifically examined, assuming it to be a valid "proxy" for the more general process of puberty. In comparison with the effects of genetics, nutrition, and general health, social influences are small, shifting timing by a few months rather than years. The most important part of a child's psychosocial environment is the family.

Some of the aspects of family structure and function reported to be independently associated with earlier menarche [antenatal and early childhood]

• Are non-white
• Experienced pre-eclampsia in the womb
• Are singletons
• Had a low birthweight
• Were not breast-fed
• Were exposed to smoking
• Absence of father from the home from early childhood
• High-conflict family relationships
• The increased incidence of childhood obesity.
• Lacked exercise in childhood

Other research has focused on the effect of childhood stress on timing of puberty, especially female. Stress is a vague term and studies have examined conditions ranging from family tensions or conflict to wartime refugee status with threat to physical survival. The more dire social conditions have been found to be associated with delay of maturation, an effect that may be compounded by dietary inadequacy. There is more uncertainty and mixed evidence as to whether milder degrees of stress or early-life under-nutrition can accelerate puberty in girls as would be predicted by life history theory and demonstrated in many other mammals.

The understanding of these environmental effects is incomplete and the following observations and cautions are relevant:

• Mechanisms of these social effects are unknown, though a variety of physiological processes, including pheromones, have been suggested based on animal research.
• Most of these "effects" are statistical associations revealed by epidemiologic surveys. Statistical associations are not necessarily causal, and a variety of secondary variables and alternative explanations can be possibly intervening. Effects of such small size can never be confirmed or refuted for any individual child.
• Despite the small magnitude of effect, interpretations of the data are politically controversial because of the ease with which this type of research can be used for political advocacy. Accusations of bias based on political agenda sometimes accompany scientific criticism.
• Correlation does not imply causation. While correlation can be objectively measured, causation is statistically inferred. Some suggest that childhood stress is caused by precocious puberty recognized later, rather than being the cause of it.

Changes in time of average age

There were few systematic studies of timing of menarche before the later half of the 20th century. Most older estimates of average timing of menarche were based on observation of a small homogeneous population not necessarily representative of the larger population, or based on recall by adult women, which is also susceptible to various forms of error. Most sources agree that the average age of menarche in girls in modern societies has declined, though the reasons and the degree remain subjects of controversy. From the sixth to the fifteenth centuries in Europe, most women reached menarche on average at about 14, between the ages of 12 and 15. A large North American survey reported only a 2-3 month decline from the mid-1970s to the mid-1990s. A 2011 study found that each 1 kg/m² increase in childhood body-mass index (BMI) can be expected to result in a 6.5% higher absolute risk of early menarche (before age 12 years).

Fewer than 10% of U.S. girls start to menstruate before 11 years of age, and 90% of all US girls are menstruating by 13.75 years of age, with a median age of 12.43 years. This age at menarche is not much different (0.34 years earlier) than that reported for U.S. girls in 1973. Age at menarche for non-Hispanic black girls was significantly earlier than that of white girls at 10%, 25%, and 50% of those who had attained menarche, whereas Mexican American girls were only slightly earlier than the white girls at 25%.

Culture

Menstruation is a cultural as well as scientific phenomenon as many societies have specific rituals and cultural norms associated with it. These rituals typically begin at menarche and some are enacted during each menstruation cycle. The rituals are important in determining a status change for girls. Upon menarche and completion of the ritual, they have become a woman as defined by their culture.

For young women in many cultures, the first menstruation is a marker that signifies a change in status. Post-menarche, the young woman enters a stage called maidenhood, the stage between menarche and marriage. There are cultures that have in past centuries, and in present, practiced rites of passage for a girl experiencing menarche.

Celebratory ceremonies

In some cultures, a party, or celebration is thrown to show the girl's transition to womanhood. This party is similar to the quinceañera in Latin America, except that a specific age marks the transition rather than menarche. In Morocco, the girl is thrown a celebration. All of her family members are invited and the girl is showered with money and gifts.

When a Japanese girl has her first period, the family sometimes celebrates by eating red-colored rice and beans (sekihan). The color of blood and the red of sekihan are not related. All the rice of ancient times of Japan was red. Since rice was precious in ancient Japan (usually, millet was eaten), it was eaten only during the celebration. Sekihan is the tradition of an ancient custom. The celebration is kept a secret from extended family until the rice is served.

In some Indian communities, young women are given a special menarche ceremony called Ruthu Sadangu.

The Mescalero Apaches place high importance on their menarche ceremony and it is regarded as the most important ritual in their tribe. Each year there is an eight-day event celebrating all of the girls who have menstruated in the past year. The days are split between feasting and private ceremonies reflecting on their new womanly status.

Religious rituals and/or ceremonies

In Nepal, Kumaris are girls worshiped as goddesses by Hindus and some Buddhists. At the onset of menarche it is believed the goddess spirit vacates her body and she is returned to ordinary life after a series of rituals.

Rituals of learning

In Australia, the Aborigines treat a girl to "love magic". She is taught the ways of womanhood by the other women in her tribe. Her mother builds her a hut to which she confines herself for the remainder of her menses. The hut is burned and she is submerged in the river at the end of menstruation. When she returns to the village, she is paired with a man who will be her husband.

In the United States, public schools have a sex education program that teaches girls about menstruation and what to expect at the onset of menarche (often this takes place during the 4th grade). Historically menstruation has been a social taboo and girls were taught about menarche and menstruation by their mothers or a female role model. Then, and to an extent now, menstruation was a private matter and a girl's menarche was not a community phenomenon.

Rituals of cleansing or purification

The Ulithi tribe of Micronesia call a girl's menarche kufar. She goes to a menstrual house, where the women bathe her and recite spells. She will have to return to the menstruation hut every time she menstruates. Her parents build her a private hut that she will live in until she is married.

In Sri Lanka an astrologer is contacted to study the alignment of stars when the girl experiences menarche because it is believed that her future can be predicted. The women of the family then gather in her home and scrub her in a ritual bathing ceremony. Her family then throws a familial party at which the girl wears white and may receive gifts.

In Ethiopia, Beta Jewish woman were separated from male society and sent to menstruation huts during menarche and every menstruation following as the blood associated with menstruation in the Beta Jewish culture was believed to be impure. The Beta Jews built their villages surrounding and near bodies of water specifically for their women to have a place to clean themselves. The menstruation huts were built close to these bodies of water.

Rituals of transformation and scarification

In Nigeria, the Tiv ethnic group cut four lines into the abdomen of their girls during menarche. The lines are supposed to represent fertility.

Rituals of strength

The Navajo have a celebration called kinaalda (kinn-all-duh). Girls are expected to demonstrate their strength through footraces. The girls make a cornmeal pudding for the tribe to taste. The girls who experience menarche wear special clothes and style their hair like the Navajo goddess "Changing Woman".

The Nuu-chah-nulth (also known as the Nootka) believe that physical endurance is the most important quality in young women. At menarche the girl is taken out to sea and left there to swim back.

Menstruation, also known as a period or monthly, is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The first period usually begins between twelve and fifteen years of age, a point in time known as menarche. However, periods may occasionally start as young as eight years old and still be considered normal. The average age of the first period is generally later in the developing world, and earlier in the developed world. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days). Bleeding usually lasts around 2 to 7 days. Menstruation stops occu rring after menopause, which usually occurs between 45 and 55 years of age. Periods also stop during pregnancy and typically do not resume during the initial months of breastfeeding.

Up to 80% of women report having some symptoms prior to menstruation. Common signs and symptoms include acne, tender breasts, bloating, feeling tired, irritability, and mood changes. These may interfere with normal life, therefore qualifying as premenstrual syndrome, in 20 to 30% of women. In 3 to 8%, symptoms are severe.

A lack of periods, known as amenorrhea, is when periods do not occur by age 15 or have not occurred in 90 days. Other problems with the menstrual cycle include painful periods and abnormal bleeding such as bleeding between periods or heavy bleeding. Menstruation in other animals occurs in primates, such as apes and monkeys, as well as bats and the elephant shrew.

The menstrual cycle occurs due to the rise and fall of hormones. This cycle results in the thickening of the lining of the uterus, and the growth of an egg, (which is required for pregnancy). The egg is released from an ovary around day fourteen in the cycle; the thickened lining of the uterus provides nutrients to an embryo after implantation. If pregnancy does not occur, the lining is released in what is known as menstruation.

Onset and frequency

The first menstrual period occurs after the onset of pubertal growth, and is called menarche. The average age of menarche is 12 to 15. However, it may start as early as eight. The average age of the first period is generally later in the developing world, and earlier in the developed world. The average age of menarche has changed little in the United States since the 1950s.

Menstruation is the most visible phase of the menstrual cycle and its beginning is used as the marker between cycles. The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days).

Perimenopause is when fertility in a female declines, and menstruation occurs less regularly in the years leading up to the final menstrual period, when a female stops menstruating completely and is no longer fertile. The medical definition of menopause is one year without a period and typically occurs between 45 and 55 in Western countries.

During pregnancy and for some time after childbirth, menstruation does not occur; this state is known as amenorrhoea. If menstruation has not resumed, fertility is low during lactation. The average length of postpartum amenorrhoea is longer when certain breastfeeding practices are followed; this may be done intentionally as birth control.

Health effects

In most women, various physical changes are brought about by fluctuations in hormone levels during the menstrual cycle. This includes muscle contractions of the uterus (menstrual cramping) that can precede or accompany menstruation. Some may notice water retention, changes in sex drive, fatigue, breast tenderness, or nausea. Breast swelling and discomfort may be caused by water retention during menstruation. Usually, such sensations are mild, and some females notice very few physical changes associated with menstruation. A healthy diet, reduced consumption of salt, caffeine and alcohol, and regular exercise may be effective for women in controlling some symptoms. Severe symptoms that disrupt daily activities and functioning may be diagnosed as premenstrual dysphoric disorder. Symptoms before menstruation are known as premenstrual molimina.

Cramps

Many women experience painful cramps, also known as dysmenorrhea, during menstruation. Pain results from ischemia and muscle contractions. Spiral arteries in the secretory endometrium constrict, resulting in ischemia to the secretory endometrium. This allows the uterine lining to slough off. The myometrium contracts spasmodically in order to push the menstrual fluid through the cervix and out of the vagina. The contractions are mediated by a release of prostaglandins.

Painful menstrual cramps that result from an excess of prostaglandin release are referred to as primary dysmenorrhea. Primary dysmenorrhea usually begins within a year or two of menarche, typically with the onset of ovulatory cycles. Treatments that target the mechanism of pain include non-steroidal anti-inflammatory drugs (NSAIDs) and hormonal contraceptives. NSAIDs inhibit prostaglandin production. With long-term treatment, hormonal birth control reduces the amount of uterine fluid/tissue expelled from the uterus. Thus resulting in shorter, less painful menstruation. These drugs are typically more effective than treatments that do not target the source of the pain (e.g. acetaminophen). Risk factors for primary dysmenorrhea include: early age at menarche, long or heavy menstrual periods, smoking, and a family history of dysmenorrhea. Regular physical activity may limit the severity of uterine cramps.

For many women, primary dysmenorrhea gradually subsides in late second generation. Pregnancy has also been demonstrated to lessen the severity of dysmenorrhea, when menstruation resumes. However, dysmenorrhea can continue until menopause. 5â€"15% of women with dysmenorrhea experience symptoms severe enough to interfere with daily activities.

Secondary dysmenorrhea is the diagnosis given when menstruation pain is a secondary cause to another disorder. Conditions causing secondary dysmenorrhea include endometriosis, uterine fibroids, and uterine adenomyosis. Rarely, congenital malformations, intrauterine devices, certain cancers, and pelvic infections cause secondary dysmenorrhea. Symptoms include pain spreading to hips, lower back and thighs, nausea, and frequent diarrhea or constipation. If the pain occurs between menstrual periods, lasts longer than the first few days of the period, or is not adequately relieved by the use of non-steroidal anti-inflammatory drugs (NSAIDs) or hormonal contraceptives, women should be evaluated for secondary causes of dysmenorrhea.

When severe pelvic pain and bleeding suddenly occur or worsen during a cycle, the woman or girl should be evaluated for ectopic pregnancy and spontaneous abortion. This evaluation begins with a pregnancy test and should be done as soon as unusual pain begins, because ectopic pregnancies can be lifeâ€'threatening.

In some cases, stronger physical and emotional or psychological sensations may interfere with normal activities, and include menstrual pain (dysmenorrhea), migraine headaches, and depression. Dysmenorrhea, or severe uterine pain, is particularly common for young females (one study found that 67.2% of girls aged 13â€"19 have it).

The medications in the non-steroidal anti-inflammatory drugs (NSAIDs) class are commonly used to relieve menstrual cramps. Some herbs are also claimed to help.

Mood and behavior

Some women experience emotional disturbances starting one or two weeks before their period, and stopping soon after the period has started. Symptoms may include mental tension, irritability, mood swings, and crying spells. Problems with concentration and memory may occur. There may also be depression or anxiety.

This is part of premenstrual syndrome (PMS) and is estimated to occur in 20 to 30% of women. In 3 to 8% it is severe.

More severe symptoms of anxiety or depression may be signs of premenstrual dysphoric disorder (PMDD). Rarely, in individuals who are susceptible, menstruation may be a trigger for menstrual psychosis.

Bleeding

The average volume of menstrual fluid during a monthly menstrual period is 35 milliliters (2.4 tablespoons of menstrual fluid) with 10â€"80 milliliters (1â€"6 tablespoons of menstrual fluid) considered typical. Menstrual fluid is the correct name for the flow, although many people prefer to refer to it as menstrual blood. Menstrual fluid contains some blood, as well as cervical mucus, vaginal secretions, and endometrial tissue. Menstrual fluid is reddish-brown, a slightly darker color than venous blood.

Unless a woman has a bloodborne illness, menstrual fluid is harmless. No toxins are released in menstrual flow, as this is a lining that must be pure and clean enough to have nurtured a baby. Menstrual fluid is no more dangerous than regular blood.

About half of menstrual fluid is blood. This blood contains sodium, calcium, phosphate, iron, and chloride, the extent of which depends on the woman. As well as blood, the fluid consists of cervical mucus, vaginal secretions, and endometrial tissue. Vaginal fluids in menses mainly contribute water, common electrolytes, organ moieties, and at least 14 proteins, including glycoproteins.

Many mature females notice blood clots during menstruation. These appear as clumps of blood that may look like tissue. If there are questions (for example, was there a miscarriage?), examination under a microscope can confirm if it was endometrial tissue or pregnancy tissue (products of conception) that was shed. Sometimes menstrual clots or shed endometrial tissue is incorrectly thought to indicate an early-term miscarriage of an embryo. An enzyme called plasmin â€" contained in the endometrium â€" tends to inhibit the blood from clotting.

The amount of iron lost in menstrual fluid is relatively small for most women. In one study, premenopausal women who exhibited symptoms of iron deficiency were given endoscopies. 86% of them actually had gastrointestinal disease and were at risk of being misdiagnosed simply because they were menstruating. Heavy menstrual bleeding, occurring monthly, can result in anemia.

Menstrual disorders

There is a wide spectrum of differences in how women experience menstruation. There are several ways that someone's menstrual cycle can differ from the norm, any of which should be discussed with a doctor to identify the underlying cause:

There is a movement among gynecologists to discard the terms noted above, which although they are widely used, do not have precise definitions. Many now argue to describe menstruation in simple terminology, including:

• Cycle regularity (irregular, regular, or absent)
• Frequency of menstruation (frequent, normal, or infrequent)
• Duration of menstrual flow (prolonged, normal, or shortened)
• Volume of menstrual flow (heavy, normal, or light)

Dysfunctional uterine bleeding is a hormonally caused bleeding abnormality. Dysfunctional uterine bleeding typically occurs in premenopausal women who do not ovulate normally (i.e. are anovulatory). All these bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant women may bleed, a pregnancy test forms part of the evaluation of abnormal bleeding.

Women who had undergone female genital mutilation (particularly type III- infibulation) a practice common in parts of Africa, may experience menstrual problems, such as slow and painful menstruation, that is caused by the near-complete sealing off of the vagina.

Premature or delayed menarche should be investigated if menarche begins before 9 years, if menarche has not begun by age 15, if there is no breast development by age 13, or if there is no period by 3 years after the onset of breast development.

Ovulation suppression

Birth control

Since the late 1960s, many women have chosen to control the frequency of menstruation with hormonal birth control pills. They are most often combined hormone pills containing estrogen and are taken in 28-day cycles, 21 hormonal pills with either a 7-day break from pills, or 7 placebo pills during which the woman menstruates. Hormonal birth control acts by using low doses of hormones to prevent ovulation, and thus prevent pregnancy in sexually active women. But by using placebo pills for a 7-day span during the month, a regular bleeding period is still experienced.

Injections such as depo-provera became available in the 1960s. Progestogen implants such as Norplant in the 1980s and extended cycle combined oral contraceptive pills in the early 2000s.

Using synthetic hormones, it is possible for a woman to completely eliminate menstrual periods. When using progestogen implants, menstruation may be reduced to 3 or 4 menstrual periods per year. By taking progestogen-only contraceptive pills (sometimes called the 'mini-pill') continuously without a 7-day span of using placebo pills, menstrual periods do not occur. Some women do this simply for convenience in the short-term, while others prefer to eliminate periods altogether when possible.

Some women use hormonal contraception in this way to eliminate their periods for months or years at a time, a practice called menstrual suppression. When the first birth control pill was being developed, the researchers were aware that they could use the contraceptive to space menstrual periods up to 90 days apart, but they settled on a 28-day cycle that would mimic a natural menstrual cycle and produce monthly periods. The intention behind this decision was the hope of the inventor, John Rock, to win approval for his invention from the Roman Catholic Church. That attempt failed, but the 28-day cycle remained the standard when the pill became available to the public. There is debate among medical researchers about the potential long-term impacts of these practices upon female health. Some researchers point to the fact that historically, females have had far fewer menstrual periods throughout their lifetimes, a result of shorter life expectancies, as well as a greater length of tim e spent pregnant or breast-feeding, which reduced the number of periods experienced by females. These researchers believe that the higher number of menstrual periods by females in modern societies may have a negative impact upon their health. On the other hand, some researchers believe there is a greater potential for negative impacts from exposing females perhaps unnecessarily to regular low doses of synthetic hormones over their reproductive years.

Breastfeeding

Breastfeeding causes negative feedback to occur on pulse secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). Depending on the strength of the negative feedback, breastfeeding women may experience complete suppression of follicular development, follicular development but no ovulation, or normal menstrual cycles may resume. Suppression of ovulation is more likely when suckling occurs more frequently. The production of prolactin in response to suckling is important to maintaining lactational amenorrhea. On average, women who are fully breastfeeding whose infants suckle frequently experience a return of menstruation at fourteen and a half months postpartum. There is a wide range of response among individual breastfeeding women, however, with some experiencing return of menstruation at two months and others remaining amenorrheic for up to 42 months postpartum.

Menstrual management

Menstruation is managed by menstruating women to avoid damage to clothing or to accord with norms of public life. Menstrual management practices range from medical suppression of menstruation, through wearing special garments or other items, washing or avoidance of washing, disposal and laundry of stained materials, to separation of menstruators to particular places or activities.

Menstrual products (also called "feminine hygiene" products) are made to absorb or catch menstrual blood. A number of different products are available - some are disposable, some are reusable. Where women can afford it, items used to absorb or catch menses are usually commercially manufactured products. In developing countries, many women may not afford these products and use materials found in the environment or other improvised materials.

Disposable items

• Sanitary napkins (Sanitary towels) or pads â€" Somewhat rectangular pieces of material worn in the underwear to absorb menstrual flow, often with "wings", pieces that fold around the undergarment and/or an adhesive backing to hold the pad in place. Disposable pads may contain wood pulp or gel products, usually with a plastic lining and bleached. Some sanitary napkins, particularly older styles, are held in place by a belt-like apparatus, instead of adhesive or wings.
• Tampons â€" Disposable cylinders of treated rayon/cotton blends or all-cotton fleece, usually bleached, that are inserted into the vagina to absorb menstrual flow.
• Padettes â€" Disposable wads of treated rayon/cotton blend fleece that are placed within the inner labia to absorb menstrual flow.
• Disposable menstrual cups â€" A firm, flexible cup-shaped device worn inside the vagina to catch menstrual flow. Disposable cups are made of soft plastic.

Reusable items

• Reusable cloth pads â€" Pads that are made of cotton (often organic), terrycloth, or flannel, and may be handsewn (from material or reused old clothes and towels) or storebought.
• Menstrual cups â€" A firm, flexible bell-shaped device worn inside the vagina for about half a day or overnight to catch menstrual flow. They are emptied into the toilet or sink when full, washed and re-inserted (washing hands with soap before doing so is crucial). Menstrual cups are usually made of silicone and can last 5 years or longer. At the end of the period, they are sterilised, usually by boiling in water.
• Sea sponges â€" Natural sponges, worn internally like a tampon to absorb menstrual flow.
• Padded panties â€" Reusable cloth (usually cotton) underwear with extra absorbent layers sewn in to absorb flow.
• Blanket, towel â€" (also known as a draw sheet) â€" large reusable piece of cloth, most often used at night, placed between legs to absorb menstrual flow.

Non-commercial materials

Absorption materials that may be used by women who cannot afford anything else include: sand, ash, small hole in earth, cloth - new or re-used, whole leaf, leaf fibre (such as water hyacinth, banana, papyrus, cotton fibre), paper (toilet paper, re-used newspaper, pulped and dried paper), animal pelt e.g. goat skin, double layer of underwear, skirt or sari.

Society and culture

Traditions and taboos

Many religions have menstruation-related traditions, for example the laws of Niddah in Judaism. These may ban certain actions during menstruation (such as sexual intercourse in some movements of Judaism and Islam), or rituals performed at the end of each menses (such as the mikvah in Judaism and the ghusl in Islam). Some traditional societies sequester women in residences called "menstrual huts" that are reserved for that exclusive purpose.

In Hinduism, it is also frowned upon to go to a temple and do pooja (i.e., pray) or do pooja at religious events if you are menstruating. Saraswati, the Hindu goddess of knowledge, is associated with menstruation; the literal translation of her name is "flow â€" woman". Metaformic Theory, as proposed by cultural theorist Judy Grahn and others, places menstruation as a central organizing idea in the creation of culture and the formation of humans' earliest rituals.

Although most Christian denominations do not follow any specific or prescribed rites for menstruation, the Western civilization, which has been predominantly Christian, has a history of menstrual taboos, with menstruating women having been believed to be dangerous.

Anthropologists, Lock and Nguyen (2010), have noted that the heavy medicalization of the reproductive life-stages of women in the West, mimic power structures that are deemed, in other cultural practices, to function as a form of "social control". Medicalization of the stages of women's lives, such as birth and menstruation, has enlivened a feminist perspective that investigates the social implications of biomedicine’s practice. "[C]ultural analysis of reproduction…attempts to show how women…exhibit resistance and create dominant alternative meanings about the body and reproduction to those dominant among the medical profession."

In some parts of South Asia, women are isolated during menstruation. In 2005, in Nepal, the Supreme Court abolished the practice of chhaupadi, keeping women in cow-sheds during menstruation.

Sexual activity

Sexual intercourse during menstruation does not cause damage in and of itself, but the woman's body is more vulnerable during this time. Vaginal pH is higher and less acidic than normal, the cervix is lower in its position, the cervical opening is more dilated, and the uterine endometrial lining is absent, thus allowing organisms direct access to the blood stream through the numerous blood vessels that nourish the uterus. All these conditions increase the chance of infection during menstruation.

Other aspects

Male menstruation is a term used colloquially for a type of bleeding in the urine or faeces of males, reported in some tropical countries. It is actually caused by parasite infestation of the urinary tract or intestines by Schistosoma haematobium, and cases of it are actually schistosomiasis, formerly known as bilharziasis.

Evolution

All female placental mammals have a uterine lining that builds up when the animal is fertile, but it is dismantled when the animal is infertile. Most female mammals have an estrous cycle, yet only primates (including humans), several species of bats, and elephant shrews have a menstrual cycle. Some anthropologists have questioned the energy cost of rebuilding the endometrium every fertility cycle. However, anthropologist Beverly Strassmann has proposed that the energy savings of not having to continuously maintain the uterine lining more than offsets energy cost of having to rebuild the lining in the next fertility cycle, even in species such as humans where much of the lining is lost through bleeding (overt menstruation) rather than reabsorbed (covert menstruation).

Many have questioned the evolution of overt menstruation in humans and related species, speculating on what advantage there could be to losing blood associated with dismantling the endometrium, rather than absorbing it, as most mammals do. Humans do, in fact, reabsorb about two-thirds of the endometrium each cycle. Strassmann asserts that overt menstruation occurs not because it is beneficial in itself. Rather, the fetal development of these species requires a more developed endometrium, one which is too thick to reabsorb completely. Strassman correlates species that have overt menstruation to those that have a large uterus relative to the adult female body size.

Beginning in 1971, some research suggested that menstrual cycles of cohabiting human females became synchronized. A few anthropologists hypothesized that in hunter-gatherer societies, males would go on hunting journeys whilst the females of the tribe were menstruating, speculating that the females would not have been as receptive to sexual relations while menstruating. However, there is currently significant dispute as to whether menstrual synchrony exists.

Auditory processing disorder (APD), also known as central auditory processing disorder (CAPD), is an umbrella term for a variety of disorders that affect the way the brain processes auditory information. Individuals with APD usually have normal structure and function of the outer, middle and inner ear (peripheral hearing). However, they cannot process the information they hear in the same way as others do, which leads to difficulties in recognizing and interpreting sounds, especially the sounds composing speech. It is thought that these difficulties arise from dysfunction in the central nervous system.

The American Academy of Audiology notes that APD is diagnosed by difficulties in one or more auditory processes known to reflect the function of the central auditory nervous system.

APD can affect both children and adults, although the actual prevalence is currently unknown. It has been suggested that males are twice as likely to be affected by the disorder as females, but there are no good epidemiological studies.

Definitions

The American Speech-Language-Hearing Association (ASHA) published "(Central) Auditory Processing Disorders" in January 2005 as an update to the "Central Auditory Processing: Current Status of Research and Implications for Clinical Practice (ASHA, 1996)". The American Academy of Audiology has released more current practice guidelines related to the disorder

In 2011, the British Society of Audiology published 'best practice guidelines'.

Auditory processing disorder can be developmental or acquired. It may result from ear infections, head injuries or neurodevelopmental delays that affect processing of auditory information. This can include problems with: "...sound localization and lateralization (see also binaural fusion); auditory discrimination; auditory pattern recognition; temporal aspects of audition, including temporal integration, temporal discrimination (e.g., temporal gap detection), temporal ordering, and temporal masking; auditory performance in competing acoustic signals (including dichotic listening); and auditory performance with degraded acoustic signals."

The Committee of UK Medical Professionals Steering the UK Auditory Processing Disorder Research Program have developed the following working definition of Auditory Processing Disorder: "APD results from impaired neural function and is characterized by poor recognition, discrimination, separation, grouping, localization, or ordering of speech sounds. It does not solely result from a deficit in general attention, language or other cognitive processes."

History

The first research into APD began in 1954 with Helmer Myklebust’s study, "Auditory Disorders in Children". Myklebust’s work suggested auditory processing disorder was separate from language learning difficulties. His work sparked interest in auditory deficits after acquired brain lesions affecting the temporal lobes and led to additional work looking at the physiological basis of auditory processing, but it was not until the late seventies and early eighties that research began on APD in depth. In 1977, the first conference on the topic of APD was organized by Robert W. Keith, Ph.D. at the University of Cincinnati. The proceedings of that conference was published by Grune and Stratton under the title "Central Auditory Dysfunction" (Keith RW Ed.) That conference started a new series of studies focusing on APD in children. Virtually all tests currently used to diagnose APD originate from this work. These early researchers also invented many of the auditory traini ng approaches, including interhemispheric transfer training and interaural intensity difference training. This period gave us a rough understanding of the causes and possible treatment options for APD. Much of the work in the late nineties and 2000s has been looking to refining testing, developing more sophisticated treatment options, and looking for genetic risk factors for APD. Scientists have worked on improving behavioral tests of auditory function, neuroimaging, electroacoustic, and electrophysiologic testing. Working with new technology has led to a number of software programs for auditory training. With global awareness of mental disorders and increasing understanding of neuroscience, auditory processing is more in the public and academic consciousness than ever before.

Diagnosis

APD is a difficult disorder to detect and diagnose. The subjective symptoms that lead to an evaluation for APD include an intermittent inability to process verbal information, leading the person to guess to fill in the processing gaps. There may also be disproportionate problems with decoding speech in noisy environments.

APD has been defined anatomically in terms of the integrity of the auditory areas of the nervous system. However, children with symptoms of APD typically have no evidence of neurological disease and the diagnosis is made on the basis of performance on behavioral auditory tests. Auditory processing is "what we do with what we hear", and in APD there is a mismatch between peripheral hearing ability (which is typically normal) and ability to interpret or discriminate sounds. Thus in those with no signs of neurological impairment, APD is diagnosed on the basis of auditory tests. There is, however, no consensus as to which tests should be used for diagnosis, as evidenced by the succession of task force reports that have appeared in recent years. The first of these occurred in 1996. This was followed by a conference organized by the American Academy of Audiology. Experts attempting to define diagnostic criteria have to grapple with the problem that a child may do poorly on an auditory t est for reasons other than poor auditory perception: for instance, failure could be due to inattention, difficulty in coping with task demands, or limited language ability. In an attempt to rule out at least some of these factors, the American Academy of Audiology conference explicitly advocated that for APD to be diagnosed, the child must have a modality-specific problem, i.e. affecting auditory but not visual processing. However, an ASHA committee subsequently rejected modality-specificity as a defining characteristic of auditory processing disorders.

The issue of modality-specificity has led to considerable debate among experts in this field. Cacace and McFarland have argued that APD should be defined as a modality-specific perceptual dysfunction that is not due to peripheral hearing loss. They criticise more inclusive conceptualizations of APD as lacking diagnostic specificity. A requirement for modality-specificity could potentially avoid including children whose poor auditory performance is due to general factors such as poor attention or memory. Others, however, have argued that a modality-specific approach is too narrow, and that it would miss children who had genuine perceptual problems affecting both visual and auditory processing. It is also impractical, as audiologists do not have access to standardized tests that are visual analogs of auditory tests. The debate over this issue remains unresolved. It is clear, however, that a modality-specific approach will diagnose fewer children with APD than a modality-gener al one, and that the latter approach runs a risk of including children who fail auditory tests for reasons other than poor auditory processing. Although modality-specific testing has been advocated for well over a decade, to date no tests have been published which would allow audiologists to perform a modality-specific evaluation (i.e., no clinical versions of visual analogs to auditory processing tests exist).

Another controversy concerns the fact that most traditional tests of APD use verbal materials. The British Society of Audiology has embraced Moore's (2006) recommendation that tests for APD should assess processing of non-speech sounds. The concern is that if verbal materials are used to test for APD, then children may fail because of limited language ability. An analogy may be drawn with trying to listen to sounds in a foreign language. It is much harder to distinguish between sounds or to remember a sequence of words in a language you do not know well: the problem is not an auditory one, but rather due to lack of expertise in the language.

In recent years there have been additional criticisms of some popular tests for diagnosis of APD. Tests that use tape-recorded American English have been shown to over-identify APD in speakers of other forms of English. Performance on a battery of non-verbal auditory tests devised by the Medical Research Council's Institute of Hearing Research was found to be heavily influenced by non-sensory task demands, and indices of APD had low reliability when this was controlled for. This research undermines the validity of APD as a distinct entity in its own right and suggests that the use of the term "disorder" itself is unwarranted. In a recent review of such diagnostic issues, it was recommended that children with suspected auditory processing impairments receive a holistic psychometric assessment including general intellectual ability, auditory memory, and attention, phonological processing, language, and literacy. The authors state that "a clearer understanding of the relative contrib utions of perceptual and non-sensory, unimodal and supramodal factors to performance on psychoacoustic tests may well be the key to unravelling the clinical presentation of these individuals."

Depending on how it is defined, APD may share common symptoms with ADD/ADHD, specific language impairment, Asperger syndrome and other forms of autism. A review showed substantial evidence for atypical processing of auditory information in children with autism. Dawes and Bishop noted how specialists in audiology and speech-language pathology often adopted different approaches to child assessment, and they concluded their review as follows: "We regard it as crucial that these different professional groups work together in carrying out assessment, treatment and management of children and undertaking cross-disciplinary research." In practice, this seems rare.

Causes

Acquired auditory processing disorder

Acquired APD can be caused by any damage to or dysfunction of the central auditory nervous system and can cause auditory processing problems. For an overview of neurological aspects of APD, see Griffiths.

Hereditary and genetic characteristics of central auditory processing disorder

The ability to listen to and comprehend multiple messages at the same time is a trait that is heavily influenced by our genes say federal researchers. These "short circuits in the wiring" sometimes run in families or result from a difficult birth, just like any learning disability. Auditory processing disorder can be associated with conditions affected by genetic traits, such as various developmental disorders. Inheritance of Auditory Processing Disorder refers to whether the condition is inherited from your parents or "runs" in families. Central auditory processing disorder may be hereditary neurological traits from the mother or the father.

Developmental auditory processing disorder

In the majority of cases of developmental APD, the cause is unknown. An exception is acquired epileptic aphasia or Landau-Kleffner syndrome, where a child's development regresses, with language comprehension severely affected. The child is often thought to be deaf, but normal peripheral hearing is found. In other cases, suspected or known causes of APD in children include delay in myelin maturation, ectopic (misplaced) cells in the auditory cortical areas, or genetic predisposition. In a family with autosomal dominant epilepsy, seizures which affected the left temporal lobe seemed to cause problems with auditory processing. In another extended family with a high rate of APD, genetic analysis showed a haplotype in chromosome 12 that fully co-segregated with language impairment.

Hearing begins in utero, but the central auditory system continues to develop for at least the first decade. There is considerable interest in the idea that disruption to hearing during a sensitive period may have long-term consequences for auditory development. One study showed thalamocortical connectivity in vitro was associated with a time sensitive developmental window and required a specific cell adhesion molecule (lcam5) for proper brain plasticity to occur. This points to connectivity between the thalamus and cortex shortly after being able to hear (in vitro) as at least one critical period for auditory processing. Another study showed that rats reared in a single tone environment during critical periods of development had permanently impaired auditory processing. ‘Bad’ auditory experiences, such as temporary deafness by cochlear removal in rats leads to neuron shrinkage. In a study looking at attention in APD patients, children with one ear blocked developed a strong r ight-ear advantage but were not able to modulate that advantage during directed-attention tasks.

In the 1980s and 1990s, there was considerable interest in the role of chronic Otitis media (middle ear disease or 'glue ear') in causing APD and related language and literacy problems. Otitis media with effusion is a very common childhood disease that causes a fluctuating conductive hearing loss, and there was concern this may disrupt auditory development if it occurred during a sensitive period. Consistent with this, in a sample of young children with chronic ear infections recruited from a hospital otolargyngology department, increased rates of auditory difficulties were found later in childhood. However, this kind of study will suffer from sampling bias because children with otitis media will be more likely to be referred to hospital departments if they are experiencing developmental difficulties. Compared with hospital studies, epidemiological studies, which assesses a whole population for otitis media and then evaluate outcomes, have found much weaker evidence for long-term impacts of otitis media on language outcomes.

Characteristics

The National Institute on Deafness and Other Communication Disorders state that children with Auditory Processing Disorder often:

• have trouble paying attention to and remembering information presented orally, and may cope better with visually acquired information
• have problems carrying out multi-step directions given orally; need to hear only one direction at a time
• have poor listening skills
• need more time to process information
• have low academic performance
• have behavior problems
• have language difficulties (e.g., they confuse syllable sequences and have problems developing vocabulary and understanding language)
• have difficulty with reading, comprehension, spelling, and vocabulary

APD can manifest as problems determining the direction of sounds, difficulty perceiving differences between speech sounds and the sequencing of these sounds into meaningful words, confusing similar sounds such as "hat" with "bat", "there" with "where", etc. Fewer words may be perceived than were actually said, as there can be problems detecting the gaps between words, creating the sense that someone is speaking unfamiliar or nonsense words. Those suffering from APD may have problems relating what has been said with its meaning, despite obvious recognition that a word has been said, as well as repetition of the word. Background noise, such as the sound of a radio, television or a noisy bar can make it difficult to impossible to understand speech, since spoken words may sound distorted either into irrelevant words or words that don't exist, depending on the severity of the auditory processing disorder. Using a telephone can be problematic for someone with auditory processing di sorder, in comparison with someone with normal auditory processing, due to low quality audio, poor signal, intermittent sounds and the chopping of words. Many who have auditory processing disorder subconsciously develop visual coping strategies, such as lip reading, reading body language, and eye contact, to compensate for their auditory deficit, and these coping strategies are not available when using a telephone.

As noted above, the status of APD as a distinct disorder has been queried, especially by speech-language pathologists and psychologists, who note the overlap between clinical profiles of children diagnosed with APD and those with other forms of specific learning disability. Many audiologists, however, would dispute that APD is just an alternative label for dyslexia, SLI, or ADHD, noting that although it often co-occurs with these conditions, it can be found in isolation.

Central auditory processing disorder in adults

CAPD can continue into adulthood. Cooper and Gates (1991) estimated the prevalence of adult APD to be 10 to 20%. Many people experience problems with learning and day-to-day tasks with difficulties over time. Adults with this disorder

• talk louder than necessary
• have trouble remembering a list or sequence
• often need words or sentences repeated
• have poor ability to memorize information learned by listening
• interpret words too literally
• need assistance hearing clearly in noisy environments
• rely on accommodation and modification strategies
• find or request a quiet work space away from others
• request written material when attending oral presentations
• ask for directions to be given one step at a time

Relation to specific language impairment and developmental dyslexia

There has been considerable debate over the relationship between APD and Specific language impairment (SLI).

SLI is diagnosed when a child has difficulties with understanding or producing spoken language for no obvious cause. The problems cannot be explained in terms of peripheral hearing loss. The child is typically late in starting to talk, and may have problems in producing speech sounds clearly, and in producing or understanding complex sentences. Some theoretical accounts of SLI regard it as the result of auditory processing problems. However, this view of SLI is not universally accepted, and others regard the main difficulties in SLI as stemming from problems with higher-level aspects of language processing. Where a child has both auditory and language problems, it can be hard to sort out cause-and-effect.

Similarly with developmental dyslexia, there has been considerable interest in the idea that for some children reading problems are downstream consequences of difficulties in rapid auditory processing. Again, cause and effect can be hard to unravel. This is one reason why experts such as Moore have recommended using non-verbal auditory tests to diagnose APD.

It has also been suggested that APD may be related to cluttering, a fluency disorder marked by word and phrase repetitions.

If, as is commonly done, APD is assessed using tests that involve identifying, repeating or discriminating speech, then a child may do poorly because of primary language problems. In a study comparing children with a diagnosis of dyslexia and those with a diagnosis of APD, they found the two groups could not be distinguished. obtained similar findings in studies comparing children diagnosed with SLI or APD. The two groups had very similar profiles. This raises the worrying possibility that the diagnosis that a child receives may be largely a function of the specialist they see: the same child who would be diagnosed with APD by an audiologist may be diagnosed with SLI by a speech-language therapist or with dyslexia by a psychologist.

Remediation and training

There is a lack of well-conducted evaluations of intervention using randomized controlled trial methodology. Most evidence for effectiveness adopts weaker standards of evidence, such as showing that performance improves after training. This does not control for possible influences of practice, maturation, or placebo effects. Recent research has shown that practice with basic auditory processing tasks (i.e. auditory training) may improve performance on auditory processing measures and phonemic awareness measures. Changes after auditory training have also been recorded at the physiological level. Many of these tasks are incorporated into computer-based auditory training programs such as Earobics and Fast ForWord, an adaptive software available at home and in clinics worldwide, but overall, evidence for effectiveness of these computerised interventions in improving language and literacy is not impressive. One small-scale uncontrolled study reported successful outcomes for children wi th APD using auditory training software.

Treating additional issues related to APD can result in success. For example, treatment for phonological disorders (difficulty in speech) can result in success in terms of both the phonological disorder as well as APD. In one study, speech therapy improved auditory evoked potentials (a measure of brain activity in the auditory portions of the brain).

While there is evidence that language training is effective for improving APD, there is no current research supporting the following APD treatments:

• Auditory Integration Training typically involves a child attending two 30-minute sessions per day for ten days.
• Lindamood-Bell Learning Processes (particularly, the Visualizing and Verbalizing program)
• Physical activities that require frequent crossing of the midline (e.g., occupational therapy)
• Sound Field Amplification
• Neuro-Sensory Educational Therapy

• Neurofeedback
• Use of an fm transmitter

The categorization of the past into discrete, quantified named blocks of time is called periodization. This is a list of such named time periods as defined in various fields of study. Major categorization systems include cosmological (time periods in the origin and evolution of the universe), geological (time periods in the origin and evolution of the Earth), anthropological (time periods in the origin and evolution of humans) and historical (written history).

Human time periods

These can be divided broadly into prehistorical (before history began to be recorded) and historical periods (when written records began to be kept).

In archaeology and anthropology, prehistory is subdivided around the three-age system. This list includes the use of the three-age system as well as a number of various designation used in reference to sub-ages within the traditional three.

The dates for each age can vary by region. On the geologic time scale, the Holocene epoch starts at the end of the last glacial period of the current ice age (c.10,000 BC) and continues to the present. The beginning of Mesolithic is usually considered to correspond to the beginning of the Holocene epoch.

General periods

• Prehistory â€" Period before written history
• Ancient history â€" Aggregate of past events from the beginning of recorded human history and extending as far as the Early Middle Ages or the Postclassical Era. The span of recorded history is roughly 5,000 years, beginning with Sumerian Cuneiform script, the oldest discovered form of coherent writing from the protoliterate period around the 30th century BC.
  • Protohistory â€" Period between prehistory and history, during which a culture or civilization has not yet developed writing but other cultures have already noted its existence in their own writings.
  • Classical antiquity â€" Broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world. It is the period in which Greek and Roman society flourished and wielded great influence throughout Europe, North Africa and the Middle East.
• Post-classical history â€" Period of time that immediately followed ancient history. Depending on the continent, the era generally falls between the years AD 200â€"600 and AD 1200â€"1500. The major classical civilizations the era follows are Han China (ending in 220), the Western Roman Empire (in 476), the Gupta Empire (in the 550s), and the Sasanian Empire (in 651).
  • Middle Ages â€" Lasted from the 5th to the 14th century. It began with the collapse of the Western Roman Empire and merged into the Renaissance and the Age of Discovery.
    • Early Middle Ages â€"
    • High Middle Ages â€"
    • Late Middle Ages â€"
• Modern history â€" After the post-classical era
  • Early modern period â€"
  • Late modern period â€"
    • Machine Age (1880â€"1945)
      • Age of Oil (after 1901)
      • World War I (1914â€"1918)
      • Interwar period (1918â€"1939)
        • Roaring Twenties (1920â€"1929)
        • Great Depression (1929 â€" World War II)
      • World War II (1939â€"1945)
    • Atomic Age (after 1945)
      • Post-war era (1946â€"1962)
        • The Fifties (1950â€"1959)
        • Cold War (Soviet Union and United States, and their allies, 1945â€"1989 or 1991)
          • Korean War (1950â€"1953)
          • Vietnam War (1955â€"1975)
        • Space Age (after 1957)
          • The Sixties (1960â€"1969)
    • Post-Modern (Soviet Union and United States, 1973â€"present)
      • Information Age (1970â€"present)
        • The Seventies (1970â€"1979)
        • The Eighties (1980â€"1989)
        • The Nineties (1990â€"1999)
        • The Two Thousands (2000â€"2009)
          • War on Terrorism (2001â€"present)
          • War in Afghanistan (2001â€"2014)
          • War in Iraq (2003â€"2011)
        • The Social Age (1996â€"present)
          • The Conspiracy Age (2015â€"present)
        • The Tens (2010â€"2019)
        • The Big Data age (2001â€"present)
        • The Multimedia Age (1987â€"20++)
        • The Information Age
        • The Nuclear Age (1950â€"20++)
  • Contemporary history â€" History within living memory. It shifts forward with the generations.

Historical periods around the world

The Americas

• Classic and Postclassic eras, Central America (200â€"1519)
• Early Intermediate, Middle Horizon, Late Intermediate, Late Horizon (Peru, 200â€"1534)
  • Huari, Chimú, Chincha, Chanka people, Tiwanaku, Inca
• Baroque (New World, 1600â€"1750)
• Spanish hegemony (Americas, 16th century â€" 1820s)
• Reconstruction era (United States, 1865â€"1877)
• Gilded Age (United States, 1875â€"1900)
• Progressive Era (United States, 1890sâ€"1920s)
• Information Age (United States, 1970â€"present)
  • Modern age
  • Postmodern age

Southeast Asia

• Srivijaya (Indonesia, 3rd â€" 14th centuries), Tarumanagara (358â€"723), Sailendra (8th and 9th centuries), Kingdom of Sunda (669â€"1579), Kingdom of Mataram (752â€"1045), Kediri (1045â€"1221), Singhasari (1222â€"1292), Majapahit (1293â€"1500)
• Chenla (Cambodia, 630 â€" 802) and Khmer Empire (Cambodia, 802â€"1432)
• Anterior Lý Dynasty and Triệu Việt VÆ°Æ¡ng, Third Chinese domination, Khúc Family, DÆ°Æ¡ng Đình Nghệ, Kiều Công Tiá»…n, Ngô Dynasty, The 12 Lords Rebellion, Đinh Dynasty, Prior Lê Dynasty, Lý Dynasty, Trần Dynasty, Há»" Dynasty, Fourth Chinese domination (Vietnam, 544â€"1427)

Philippines

• Neolithic-Iron Age (c.10,000 BC - AD 1000)
• Classical period (c.1000 A.D.-900 A.D)
• Late Classical period (c. AD 900-1500)
• Colonial Era (c.1600-1898, 1901-1945)
• Sovereign Era (1946â€"present)
• Marcos era Martial Law (1972-1982)
• People power EDSA revolution (1986)
• Post Martial Law (1986â€"present)

China

• Xia dynasty (2100 BC - 1600 BC)
• Shang Dynasty (1600 BC â€" 1046 BC)
• Zhou Dynasty (1200 BC â€" 500 BC)
• Warring States period (402 BC â€" 201 BC)
• Qin Dynasty (221 BC â€" 206 BC)
• Han Dynasty (206 BC â€" AD 220)
• Six Dynasties (AD 220 â€" 580)
  • Three Kingdoms (220 â€" 265)
  • Jin Dynasty (265 â€" 420)
  • Southern and Northern Dynasties (420 â€" 580)
• Sui Dynasty (580 â€" 618)
• Tang Dynasty (623 â€" 907)
• Five Dynasties and Ten Kingdoms period (907 â€" 960)
• Song Dynasty (960 â€" 1279)
  • Northern Song Dynasty (960 â€" 1127), Liao Dynasty (907 â€" 1115), Western Xia Dynasty (1038 â€" 1227)
  • Southern Song Dynasty (1127 â€" 1279), Jin dynasty (1115â€"1234), Western Xia Dynasty (1038 â€" 1227)
• Yuan Dynasty (1271 â€" 1368)
• Ming Dynasty (1368 â€" 1644)
• Qing Dynasty (1644 â€" 1912)
• Republic of China (1912 - 1949)
  • Xinhai Revolution (1911-1912)
  • Warlord Era (1918-1927)
  • Chinese Civil War (1927-1936/1946-1950)
  • Second Sino-Japanese War (1931-1945)

Central Asia

• Xiongnu (Mongolia, 220 BC â€" AD 200)
• Rouran Khaganate (Mongolia, Manchuria, Xianbei, AD 330 â€" 555)
  • Sixteen Kingdoms (Xianbei, Turkic peoples, 304 â€" 439)
• Uyghur Khaganate (Mongolia, Manchuria, Tibet, 744 - 848)
• Liao Dynasty (Khitan people, 907 â€" 1125)
• Mongol Empire (Mongolia, 1206 â€" 1380)
• Qing dynasty (Manchu China, 1692 â€" 1911)

Egypt

Template:No information on rest of Africa

• Old Kingdom (3000 BC â€" 2000 BC)
• Middle Kingdom (2000 BC â€" 1300 BC)
• New Kingdom (1550 BC â€" 1070 BC)
• Ptolemaic Kingdom (305 BC â€" 30 BC)
• Aegyptus (30 BC â€" 390 AD)
• Coptic period (300 AD â€" 900 AD)
• Fatimid Caliphate (909 â€" 1171)
• Ayyubid Dynasty (1171 â€" 1250)
• Mamluk Sultanate (1250 â€" 1517)
• Ottoman Eyalet (1517 â€" 1867)
• Khedivate (1867 â€" 1914)

Europe

• Bronze Age (c.3000 BC â€" c.1050 BC)
  • Early Aegean Civilisation (Crete, Greece and Near East; c.3000 BC â€" c.1050 BC)
• Iron Age (c.1050 BC â€" c.500 AD)
  • Greek expansion and colonisation (c.1050 BC â€" 776 BC)
  • Archaic Greece (776 BC â€" 480 BC) â€" begins with the First Olympiad, traditionally dated 776 BC
    • Archaic period (776 BC â€" 612 BC) â€" establishment of city states in Greece
    • Pre-classical period (612 BC â€" 480 BC) â€" the fall of Nineveh to the second Persian invasion of Greece
  • Classical antiquity (480 BC â€" 476 AD)
    • Classical Greece (480 BC â€" 399 BC)
    • Macedonian era (399 BC â€" 323 BC)
    • Hellenistic Greece (323 BC â€" 146 BC)
    • Late Roman Republic (147 BC â€" 27 BC)
    • Principate of the Roman Empire (27 BC â€" 284 AD)
    • Late Antiquity (284 AD â€" 500 AD)
  • Migration Period (Europe, 300 AD â€" 700 AD)
• Middle Ages (Europe, 476 â€" 1453)
  • Byzantine era (330 â€" 1453)
  • Dark Ages (Europe, 476 â€" 800)
  • Early Middle Ages (Europe, 476 â€" 1066)
    • Viking Age (Scandinavia, Europe, 793 â€" 1066)
  • High Middle Ages (Europe, 1066 â€" c.1300)
  • Late Middle Ages (Europe, c.1300 â€" 1453)
  • The Renaissance (Europe, c.1300 â€" c.1600)
• Early modern period (Europe, 1453 â€" 1789)
  • Age of Discovery (or Exploration) (Europe, c.1400 â€" 1770)
  • Polish Golden Age (Poland, 1507 â€" 1572)
  • Golden Age of Piracy 1650 â€" 1730
  • Elizabethan era (United Kingdom, 1558 â€" 1603)
  • Protestant Reformation (Europe, 16th century)
  • Classicism (Europe, 16th â€" 18th centuries)
  • Industrious Revolution, (Europe, 16th â€" 18th centuries)
  • Jacobean era (United Kingdom, 1603 â€" 1625)
  • Petrine Era (Russia, 1689 â€" 1725)
  • Age of Enlightenment (or Reason) (Europe, 18th century)
• Long nineteenth century (1789 â€" 1914)
  • Georgian era (United Kingdom, 1714 â€" 1830)
  • Industrial Revolution (Europe, United States, elsewhere 18th and 19th centuries)
  • Age of European colonialism and imperialism
  • Romantic era (1770 â€" 1850)
  • Napoleonic era (1799 â€" 1815)
  • Victorian era (United Kingdom, 1837 â€" 1901); British hegemony, much of world, around the same time period.
  • Edwardian era (United Kingdom, 1901 â€" 1914)
• First and Second World Wars (1914 â€" 1945)
• Cold War (1945 â€" 1991)
• Post-Cold War / Postmodernity (1991 â€" present)

India

• Indus Valley Civilization (2500 BC â€" 1300 BC)
• Vedic period (1500 BC â€" 500 BC)
  • Mahajanapada kingdoms
• Maurya Empire (321 BC â€" 185 BC)
• Kushan Empire (185 BC â€" 220 AD), Satavahana Empire (230 BC â€" 220 AD),
• Gupta Empire (320 AD â€" 535 AD)
• Vakatak Empire (300AD -650 AD)
• Middle kingdoms of India (1 AD â€" 1279 AD)
  • Pala Empire (750 â€" 1174)
    • Rashtrakuta Dynasty
  • Sena Empire (1070 â€" 1230)
  • Hoysala Empire (1026 â€"1343), Kakatiya Empire (1083 â€" 1323)
• Medieval India (1206 â€" 1526)
  • Vijayanagara Empire (1336 â€" 1646), Gajapati Kingdom (1434 â€" 1541), Reddy dynasty (1325 â€" 1448)
• Mughal Empire (1526 â€" 1857)
• Maratha Empire (1674-1818)
• British Raj (1858 â€" 1947)
• Independence (1947â€"present)

Japan

• Jomon period (10,500 BC â€" 400 BC)
• Yayoi period (400 BC â€" 250 AD)
• Kofun period (250 â€" 600)
• Asuka period (600 â€" 710)
• Nara period (710 â€" 794)
• Heian period (794 â€" 1185)
• Kamakura period (1185 â€" 1333)
• Muromachi period (1333 â€" 1573)
• Azuchiâ€"Momoyama period (1573 â€" 1603)
• Tokugawa shogunate (1603 â€" 1868)
• Meiji period (1868 â€" 1912)
• Taishō period (1912 â€" 1926)
• Shōwa period (1926 â€" 1989)
  • Post-occupation era (1952 â€" present)
• Heisei period (1989â€"present)

Middle East

• Ancient Near East (Sumer, 3100 BC â€" 500 BC)
  • Jemdet Nasr period (3100 BC â€" 2900 BC)
  • Early Dynastic Period (2900 BC â€" 2270 BC)
  • Akkadian Empire (2270 BC â€" 2083 BC)
  • Gutian Dynasty (2083 BC â€" 2050 BC)
  • Sumerian renaissance (2050 BC â€" 1940 BC)
  • First Babylonian Dynasty (1830 BC â€" 1531 BC), Hittites (1800 BC â€" 1178 BC)
  • Kassites (1531 BC â€" 1135 BC), Mitanni (1500 BC â€" 1300 BC)
  • Neo-Assyrian Empire (934 BC â€" 609 BC)
  • Neo-Babylonian Empire (626 BC â€" 539 BC), Medes (678 BC â€" 549 BC)
• Persian Empires (550 BC â€" 651 AD)
  • Achaemenid Empire (550 BC â€" 330 BC)
  • Conquered by Macedonian Empire (330 BC â€" 312 BC)
  • Seleucid Empire (312 BC â€" 63 BC)
  • Parthian Empire (247 BC â€" 224 AD)
  • Sasanian Empire (224 AD â€" 651 AD)
• Islamic period (7th â€" 21st centuries)
  • Rashidun Caliphate (632 â€" 661)
  • Umayyad Caliphate (661 â€" 750)
  • Islamic Golden Age (750 â€" 1300)
  • Abbasid Caliphate (750 â€" 1258), Fatimid Caliphate (909 â€" 1171)
    • Buyid dynasty (934 â€" 1055)
    • Seljuq dynasty (1055 â€" 1171)
    • Ayyubid dynasty (1171 â€" 1341)
• Ottoman Empire (1300 â€" 1923), Safavid Empire (1501â€"1736)

Mythological and astrological time periods

• Astrological ages
  • Age of Taurus
  • Age of Aries
  • Age of Pisces
  • Age of Aquarius
• Greek mythology (See also: Ages of Man)
  • Golden Age, self-sufficient
  • Silver Age, self-indulgent
  • Bronze Age, warlike
  • Heroic Age, nobly aspirant
  • Iron Age, violent
• Aztec mythology
  • Nahui-Ocelotl, Destroyed by Jaguars
  • Nahui-Ehécatl, Destroyed by Hurricane
  • Nahuiquiahuitl, Destroyed by rain of Fire
  • Nahui-Atl, Destroyed by Flood
  • Nahui-Ollin, Destroyed by Earthquakes

Marxian stages of history

The Marxian theory of history identifies five major distinct periods of history:

Primitive communism

The First Stage: is usually called primitive communism. It has the following characteristics.

• Shared property: there is no concept of ownership beyond individual possessions. All is shared by the tribe to ensure its survival.
• Hunting and gathering: tribal societies have yet to develop large scale agriculture and so their survival is a daily struggle.
• Proto-democracy: there is usually no concept of "leadership" yet. So tribes are led by the best warrior if there is war, the best diplomat if they have steady contact with other tribes and so forth.

Slave society

The Second Stage: may be called slave society, considered to be the beginning of "class society" where private property appears.

• Class: here the idea of class appears. There is always a slave-owning ruling class and the slaves themselves.
• Statism: the state develops during this stage as a tool for the slave-owners to use and control the slaves.
• Agriculture: people learn to cultivate plants and animals on a large enough scale to support large populations.
• Democracy and authoritarianism: these opposites develop at the same stage. Democracy arises first with the development of the republican city-state, followed by the totalitarian empire.
• Private property: citizens now own more than personal property. Land ownership is especially important during a time of agricultural development.

Feudalism

The Third Stage: may be called feudalism; it appears after slave society collapses. This was most obvious during the European Middle Ages when society went from slavery to feudalism.

• Aristocracy: the state is ruled by monarchs who inherit their positions, or at times marry or conquer their ways into leadership.
• Theocracy: this is a time of largely religious rule. When there is only one religion in the land and its organizations affect all parts of daily life.
• Hereditary classes: castes can sometimes form and one's class is determined at birth with no form of advancement. This was the case with India.
• Nation-state: nations are formed from the remnants of the fallen empires. Sometimes to rebuild themselves into empires once more. Such as England's transition from a province to an empire.

Capitalism

Marx pays special attention to this stage in human development. The bulk of his work is devoted to analysing the mechanisms of capitalism, which in western society classically arose "red in tooth and claw" from feudal society in a revolutionary movement. In capitalism, the profit motive rules and people, freed from serfdom, work for the capitalists for wages. The capitalist class are free to spread their laissez faire practices around the world. In the capitalist-controlled parliament, laws are made to protect wealth.

Capitalism may be considered the Fourth Stage in the sequence. It appears after the bourgeois revolution when the capitalists (or their merchant predecessors) overthrow the feudal system. Capitalism is categorized by the following:

• Market economy: In capitalism, the entire economy is guided by market forces. Supporters of laissez-faire economics argue that there should be little or no intervention from the government under capitalism. Marxists, however, such as Lenin in his Imperialism, the Highest Stage of Capitalism, argue that the capitalist government is a powerful instrument for the furtherance of capitalism and the capitalist nation-state, particularly in the conquest of markets abroad.
• Private property: The means of production are no longer in the hands of the monarchy and its nobles, but rather they are controlled by the capitalists. The capitalists control the means of production through commercial enterprises (such as corporations) which aim to maximise profit.
• Parliamentary democracy: The capitalists tend to govern through an elected centralised parliament or congress, rather than under an autocracy. Capitalist (bourgeois) democracy, although it may be extended to the whole population, does not necessarily lead to universal suffrage. Historically it has excluded (by force, segregation, legislation or other means) sections of the population such as women, slaves, ex-slaves, people of colour or those on low income. The government acts on behalf of, and is controlled by, the capitalists through various methods.
• Wages: In capitalism, workers are rewarded according to their contract with their employer. Power elites propagate the illusion that market forces mean wages converge to an equilibrium at which workers are paid for precisely the value of their services. In reality workers are paid less than the value of their productivity â€" the difference forming profit for the employer. In this sense all paid employment is exploitation and the worker is "alienated" from their work. Insofar as the profit-motive drives the market, it is impossible for workers to be paid for the full value of their labour, as all employers will act in the same manner.
• Imperialism: Wealthy countries seek to dominate poorer countries in order to gain access to raw materials and to provide captive markets for finished products. This is done directly through war, the threat of war, or the export of capital. The capitalist's control over the state can play an essential part in the development of capitalism, to the extent the state directs warfare and other foreign intervention.
• Financial institutions: Banks and capital markets such as stock exchanges direct unused capital to where it is needed. They reduce barriers to entry in all markets, especially to the poor; it is in this way that banks dramatically improve class mobility.
• Monopolistic tendencies: The natural, unrestrained market forces will create monopolies from the most successful commercial entities.

But according to Marx, capitalism, like slave society and feudalism, also has critical failings â€" inner contradictions which will lead to its downfall. The working class, to which the capitalist class gave birth in order to produce commodities and profits, is the "grave digger" of capitalism. The worker is not paid the full value of what he or she produces. The rest is surplus value â€" the capitalist's profit, which Marx calls the "unpaid labour of the working class." The capitalists are forced by competition to attempt to drive down the wages of the working class to increase their profits, and this creates conflict between the classes, and gives rise to the development of class consciousness in the working class. The working class, through trade union and other struggles, becomes conscious of itself as an exploited class. In the view of classical Marxism, the struggles of the working class against the attacks of the capitalist class will eventually lead the working class to establish its own collective control over production

Socialism

After the working class gains class consciousness and mounts a revolution against the capitalists, socialism, which may be considered the Fifth Stage, will be attained, if the workers are successful.

Marxist socialism may be characterised as follows:

• Common property: the means of production are taken from the hands of a few capitalists and put in the hands of the workers. This translates into the democratic communes controlling the means of production.
• Council democracy: Marx, basing himself on a thorough study of Paris Commune, believed that the workers would govern themselves through system of communes. He called this the dictatorship of the proletariat, which, overthrowing the dictatorship (governance) of capital, would democratically plan production and the resources of the planet.

Marx explained that, since socialism, the first stage of communism, would be "in every respect, economically, morally, and intellectually, still stamped with the birthmarks of the old society from whose womb it emerges", each worker would naturally expect to be awarded according to the amount of labor he contributes, despite the fact that each worker's ability and family circumstances would differ, so that the results would still be unequal at this stage, although fully supported by social provision.

Geologic time periods

The geologic time scale covers the extent of the existence of Earth, from about 4600 million years ago to the present day. It is marked by Global Boundary Stratotype Sections and Points. Geologic time units are (in order of descending specificity) eons, eras, periods, epochs, and ages; and the corresponding chronostratigraphic units, which measure "rock-time", are eonothems, erathems, systems, series, and stages.

The second and third timelines are each subsections of their preceding timeline as indicated by asterisks. The Cenozoic is sometimes divided into the Quaternary and Tertiary periods, although the latter is no longer used officially.

Cosmological time periods

13.8 billion years ago: The Big Bang Theory (the universe's beginnings)