What is Menopause?

Menopause is the permanent cessation of reproductive fertility occurring some time before the end of the natural lifespan. The term was originally coined to describe this reproductive change in human females, where the end of fertility is traditionally indicated by the permanent stopping of monthly menstruation or "menses". The word "menopause" literally means the "end of monthly cycles" from the Greek words ''pausis'' (cessation) and the word root ''men'' from ''mensis'' meaning (month).

In humans, menopause is the time in a woman’s life when her reproductive cycles end. It is part of a biological process that for most women is first noticed in their mid-forties. During this transition, the ovaries start producing lower levels of natural sex hormones—estrogen and progesterone. Estrogen promotes the normal development of a woman’s breasts and uterus, controls the cycle of ovulation (when an ovary releases an egg into a fallopian tube), and affects many aspects of a woman’s physical and emotional health. Progesterone controls menstruation and prepares the lining of the uterus to receive the fertilized egg.

The meaning of the word menopause has in more recent times been expanded to indicate the permanent but naturally occurring discontinuation of female fertility in many other species, even if the females of those species do not have menstrual cycles.

In adult human females who still have a uterus, and who are not pregnant or lactating, postmenopause is identified by a permanent (at least one year's) absence of monthly periods or menstruation. In women without a uterus, menopause or postmenopause is identified by a very high FSH level.

In human females, menopause usually happens more or less in midlife, signaling the end of the fertile phase of a woman's life. Menopause is perhaps most easily understood as the opposite process to menarche, the start of the monthly periods. However, menopause in women cannot satisfactorily be defined simply as the permanent "stopping of the monthly periods", because in reality what is happening to the uterus is quite secondary to the process; it is what is happening to the ovaries that is the crucial factor.

As an illustration of this point: for medical reasons, the uterus must sometimes be surgically removed (hysterectomy) in a younger woman; her periods will cease permanently, and the woman will technically be infertile, but as long as at least one of her ''ovaries'' is still functioning, the woman will ''not'' have reached menopause. Even without the presence of the uterus, ovulation and the release of the sequence of reproductive hormones will continue to cycle on, until menopause is reached. But in circumstances where a woman's ovaries are removed (oophorectomy), even if the uterus were to be left intact, the woman will immediately be in "surgical menopause".

Thus menopause is based on the natural or surgical cessation of hormone production by the ovaries, which are a part of the body's endocrine system of hormone production, in this case the hormones which make reproduction possible and can influence sexual behavior. The resultant decreased levels of circulating estrogen impacts the entire cascade of a woman's reproductive functioning, from brain to skin.

The menopause transition, and post-menopause itself, is a natural life change, not a disease state or a disorder. The transition itself can be challenging for a number of women, but for others it is not difficult.

Age

In the Western world, the most typical age range for menopause (last period) is between the ages of 40 and 60 and the average age for last period is 51 years. In some developing countries however, such as Indonesia and the Philippines, the median age of natural menopause is considerably earlier, at 44 years.

In the Western World, a woman's last period occurring between the ages of 55 to 60 is known as a "late menopause". An "early menopause" is defined as having the final period somewhere between the age of 40 to 45.

Rarely, a woman's ovaries stop working at a very early age, ranging anywhere from the age of puberty to age 40, and this is known as premature ovarian failure (POF). POF is not considered to be due to the normal effects of aging. Some known causes of premature ovarian failure include autoimmune disorders, thyroid disease, diabetes mellitus, chemotherapy, and radiotherapy. However, in the majority of spontaneous cases of premature ovarian failure, the cause is unknown.

Premature ovarian failure is diagnosed or confirmed by measuring the levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH); the levels of these hormones will be abnormally high if menopause has occurred. Rates of premature menopause have been found to be significantly higher in fraternal and identical twins; approximately 5% of twins reach menopause before the age of 40. The reasons for this are not completely understood. Transplants of ovarian tissue between identical twins have been successful in restoring fertility.

On average, women who smoke cigarettes experience menopause significantly earlier than non-smokers.

Menopause in human evolution

In contrast to males, females invest more in their gametes making them a highly valuable resource . Selection should therefore favour a quantity of ova sufficient for the female lifespan. Over-investment is resourcefully wasteful and under-investment leads to reduced fitness. Human females, however, spend over one third of their lifespan in a post-reproductive phase. Explanations of survival beyond reproductive maturation range from the non-adaptive to the adaptive.

Non-Adaptive Hypotheses

The high cost of female investment in offspring may lead to physiological deteriorations that amplify susceptibility to becoming infertile. This hypothesis suggests the reproductive lifespan in humans has been optimised, but it has proven more difficult in females and thus their reproductive span is shorter. If this hypothesis were true, age at menopause should be negatively correlated with reproductive effort and the available data does not support this.

A recent increase in female longevity due to improvements in the standard of living and social care has also been suggested . It is difficult for selection, however, to favour aid from offspring to parents and grandparents. Irrespective of living standards, adaptive responses are limited by physiological mechanisms. In other words senescence is programmed and regulated by specific genes.

Adaptive Hypotheses

The Grandmother hypothesis suggests that menopause was selected for in humans because it promotes the survival of grandchildren. According to this hypothesis, post reproductive women feed and care for children, adult nursing daughters, and grandchildren whose mothers have weaned them. Human babies require large and steady supplies of glucose to feed the growing brain. In infants in the first year of life, the brain consumes 60% of all calories, so both babies and their mothers require a dependable food supply. Some evidence suggests that hunters contribute less than half the total food budget of most hunter-gatherer societies, and often much less than half, so that foraging grandmothers can contribute substantially to the survival of grandchildren at times when mothers and fathers are unable to gather enough food for all of their children. In general, selection operates most powerfully during times of famine or other privation. So although grandmothers might not be necessary during good times, many grandchildren cannot survive without them during times of famine. Arguably, however, there is no firm consensus on the supposed evolutionary advantages (or simply neutrality) of menopause to the survival of the species in the evolutionary past.

Indeed, analysis of historical data found that the length of a female’s post-reproductive lifespan was reflected in the reproductive success of her offspring and the survival of her grandchildren. Interestingly, another study found comparative effects but only in the maternal grandmother – paternal grandmothers had a detrimental effect on infant mortality (probably due to paternity uncertainty). Differing assistance strategies for maternal and paternal grandmothers have also been demonstrated. Maternal grandmothers concentrate on offspring survival, whereas paternal grandmothers increase birth rates.

A problem concerning the grandmother hypothesis is that it requires a history of female philopatry and yet present day evidence shows that the majority of hunter-gatherer societies are patriarchal. In addition, all variations on the mother, or grandmother effect fail to explain longevity with continued spermatogenesis in males (oldest verified paternity is 94 years, 35 years beyond the oldest documented birth attributed to females). It also fails to explain the detrimental effects of losing ovarian follicular activity, such as osteoporosis, osteoarthritis, Alzheimer’s disease and coronary artery disease.

The Patriarch Hypothesis

If women survive beyond an age at which they can reproduce and men continue spermatogenesis, then old males stand to benefit greatly if they can copulate with younger females. Increased use of tools and weapons compensates for the decline in natural fighting ability with age. This serves to produce a more stable male hierarchy, where attainment of high social status and reproductive access is less reliant on physical strength.

With such a scenario older males are able to retain a competitive ability with younger males, thereby asserting a selection pressure on extending longevity in males that could retain social status. Higher ranking males may also be a more attractive mate choice.

One mechanism that could extend the lifespan is delaying the age at maturity. Offspring with a slower life history would exhibit a protracted period of dependence. If depletion of oocytes occurs at age 50, females should selectively counter this as it reduces their fecundity. Recruitment of help from kin and husbands may compensate by enabling females to reduce birth intervals by weaning offspring at an earlier age. In addition, by passing on longevity to her sons, a female would stand to gain inclusive fitness.

Social and psychological significance: the three ages

The end of fertility in midlife ushers in the third part of a woman's life, also known as the "third age". Generally speaking, women raised or living in Western countries live long enough so that half of their adult life is spent in post-menopause. For some women, the menopausal transition represents a major life change, similar to menarche in the magnitude of its social and psychological significance.

In the ancient past, menarche and menopause were considered to mark the transitions from "maiden" to "matron", and from "matron" to "crone", (in other words, from little girl to reproductive woman and then to older woman.) Although the significance of the changes that surround menarche is still fairly well recognized, in countries such as the USA, the social and psychological ramifications of the menopause transition are frequently ignored or underestimated.

During the menopause transition years, as the body responds to the rapidly changing levels of natural hormones, a number of effects may appear. Not every woman experiences bothersome levels of these effects, and the range of effects and the degree to which they appear is very variable from person to person. Effects that are due to low estrogen levels (for example vaginal atrophy and skin drying) will continue after the menopause transition years are over; however, many effects that are caused by the extreme fluctuations in hormone levels (for example hot flashes and mood changes) usually disappear or improve significantly once the perimenopause transition time has been completed. All the various possible perimenopause effects are caused by an overall drop, as well as dramatic but erratic fluctuations, in the absolute levels and relative levels of estrogens and progesterone. Some of the effects, such as formication (crawling, itching, or tingling skin sensations), may be associated directly with hormone withdrawal.

Both users and non-users of hormone replacement therapy identify lack of energy as the most frequent and distressing effect. Other effects can include vasomotor symptoms such as hot flashes and palpitations, psychological effects such as depression, anxiety, irritability, mood swings, memory problems and lack of concentration, and atrophic effects such as vaginal dryness and urgency of urination.

The average woman also has increasingly erratic menstrual periods, due to skipped ovulations. Typically, the timing of the flow becomes unpredictable. In addition the duration of the flow may be considerably shorter or longer than normal, and the flow itself may be significantly heavier or lighter than was previously the case, including sometimes long episodes of spotting. Early in the process it is not uncommon to have some 2-week cycles. Further into the process it is common to skip periods for months at a time, and these skipped periods may be followed by a heavier period. The number of skipped periods in a row often increases as the time of last period approaches. At the point when a woman of menopausal age has had no periods or spotting for 12 months she is considered to be one year into post-menopause.

Vascular instability

hot flashes or hot flushes, including night sweats and, in a few people, cold flashes
possible but contentious increased risk of atherosclerosis
migraine

Urogenital atrophy, also known as vaginal atrophy, (main article: Atrophic vaginitis)

thinning of the membranes of the vulva, the vagina, the cervix, and also the outer urinary tract, along with considerable shrinking and loss in elasticity of all of the outer and inner genital areas.
itching
dryness
bleeding
watery discharge
urinary frequency
urinary urgency
urinary incontinence
increased susceptibility to inflammation and infection, for example vaginal candidiasis, and urinary tract infections

Skeletal

osteopenia and the risk of osteoporosis gradually developing over time
joint pain, muscle pain
back pain

Skin, soft tissue

breast atrophy

breast tenderness +/- swelling

skin thinning and becoming drier
decreased elasticity of the skin
formication (itching, tingling, burning, pins and needles, or sensation of ants crawling on or under the skin)

Psychological

mood disturbance
irritability
fatigue
memory loss, and problems with concentration
depression and/or anxiety
sleep disturbances, poor quality sleep, light sleep, insomnia

Sexual

decreased libido
vaginal dryness and vaginal atrophy
problems reaching orgasm
dyspareunia or painful intercourse

Cohort studies have reached mixed conclusions about medical conditions associated with the menopause. For example, a 2007 study found that menopause was associated with hot flashes; joint pain and muscle pain; and depressed mood. In the same study, it appeared that menopause was not associated with poor sleep, decreased libido, and vaginal dryness.

Culture

The cultural context within which a woman lives can have a significant impact on the way she experiences the menopausal transition. Within the United States, social location affects the way women perceive menopause and its related biological effects. Research indicates that whether a woman views menopause as a medical issue or an expected life change is correlated with her socio-economic status . The paradigm within which a woman considers menopause also influences the way she views it: women who understand menopause as a medical condition rate it significantly more negatively than those who view it as a life transition or a symbol of aging .

Ethnicity and geographical location also play a role in the experience of menopause. U.S. women of different ethnicities report significantly different types of menopausal "symptoms". One major study found Caucasian women most likely to report what are sometimes described as psychosomatic symptoms, while African-American women were more likely to report vasomotor symptoms . Additionally, while most women in the United States have a negative view of menopause as a time of deterioration or decline, some studies indicate that Asian women have an understanding of menopause that focuses on a sense of liberation, and celebrates the freedom from the risk of pregnancy . Diverging from these conclusions, one study appeared to show that many U.S. women "experience this time as one of liberation and self-actualization."