SciTech

The complexities behind menopause and why it is of evolutionary benefit

Credit: Brooke Kuei Credit: Brooke Kuei

To those who haven’t gone through it — and even some who have — menopause is a mystifying process. Menopause is the end of a woman’s reproductive cycle.

Etymologically, menopause refers to the end of monthly cycles, coming from the Greek words for “end” and “month.” You might recognize the stem from menstruation, a woman’s monthly cycle, or menarche, the beginning of a woman’s menstrual cycle, basically the opposite of menopause.

Although menopause occurs at different times for different women, it usually happens around midlife, at 40 or 50 years old. According to the National Institute on Aging, the average age of American women when they have their last period is 51.

When a woman goes through menopause, the end result is the loss of her reproductive capabilities, marked by the end of menstrual cycles and the ovaries’ lack of function. A woman can only officially say that she has gone through menopause — that she is postmenopausal — a full year after her last period. When a woman begins the menopausal transition but has not yet had her last period, she’s in perimenopause — going through menopause. Perimenopause can begin as many as eight years before a woman’s last period and is heralded by a host of signs.

Menopause, like every period of bodily transition, is different for every woman. While hormone tests can be helpful for determining a woman’s menopausal state, they’re not always reliable, as her hormones fluctuate.

The first sign of menopause, according to the North American Menopause Society, is usually period problems. The phrase “irregular periods” is intimidating for most women; it can cover everything from having periods too close together to spotting between periods to skipping periods. Perimenopause also announces itself with a range of other effects, including the hot flashes that many people associate with menopause.

Hot flashes are, as the name implies, a feeling of warmth that suddenly spreads through the upper body, often accompanied by flushed skin and sweating. Hot flashes, clinically known as vasomotor symptoms, are caused by the hormonal changes that accompany the menopausal transition: During perimenopause, a woman’s estrogen levels are typically 20 to 30 percent lower than normal. These hormone levels cause a change in how the body regulates temperature. Researchers, however, still don’t completely understand why this happens.

For any men who are reading this and starting to feel left out, don’t worry — you can get hot flashes, too. During andropause (yes, it’s a real thing), the midlife period when a man’s testosterone levels decrease, he may experience hot flashes similar to those a woman experiences during perimenopause.

The symptoms a woman experiences during the menopausal transition are caused by a complex series of hormonal interactions. Estrogen is not just one hormone, but an overarching term that encompasses all of the hormones that affect a woman’s reproductive cycle — primarily estrone, estradiol, and estriol. All three of these hormones play different roles during a woman’s life: Estradiol is dominant during a woman’s reproductive prime, estriol is dominant during pregnancy, and estrone is dominant during and after the menopausal transition.

During a normal menstrual cycle, the ovaries produce estradiol, testosterone, and progesterone in cyclical patterns, controlled by two other hormones: pituitary follicle-stimulating hormone (FSH) and luteinising hormone. Perimenopause is marked by fluctuations in levels of estradiol and FSH as the ovaries produce less estradiol and progesterone, a pregnancy hormone.

Along with hot flashes, these changes in hormone levels lead to many other symptoms — for example, urogenital atrophy, the scientific name for the changes to the vagina that occur during the menopausal transition. These symptoms can include itching, dryness, loss of elasticity, and bladder issues, all caused by thinning tissue and a lack of natural lubrication.

Other symptoms of menopause include joint aches, night sweats (essentially nighttime hot flashes), and a variety of psychological effects from depression to irritability.

Often, it can be difficult for researchers to know what is caused primarily by menopause and what is caused by simply getting older. During postmenopause, women are at higher risk for diseases like heart disease and osteoporosis.

Menopause may sound unpleasant, but don’t worry; human women are not alone. Killer whales and pilot whales also stop reproducing years before the end of their lifetimes, and many other mammals become gradually less fertile as they age. Researchers are not totally sure why some mammals experience menopause and others don’t; one possible cause is family structure. While menopause is not usually greeted with happiness, it may actually be of evolutionary benefit for humans, and certain types of whales, to stop reproducing as they grow older so that they can help their children and other kin to reproduce.