Journal

Latest news, views, reviews

Most mammals go through the menopause – if they live long enough

Only humans and a few toothed whales undergo the menopause, many sources will tell you. But a paper by Ivana Winkler and Angela Goncalves at the German Cancer Research Center claims that the menopause is, in fact, widespread among mammals. So which is right? The surprising answer is both.

Goncalves studies how the female reproductive tract ages in mice. “It’s absolutely clear that our mice in captivity reach something that is like menopause in humans,” she says. “And yet every time that I present this work to an audience, I get the question, ‘but I thought only humans had a menopause?’”

So Goncalves and Winkler set out to establish which other mammals have a menopause by reviewing published studies.

The first issue is that most other mammals do not menstruate in the sense of bleeding when the lining of the uterus is shed. Instead, the lining of the uterus is reabsorbed.

If you define the menopause in the narrow sense of the ending of menstruation, most mammals cannot undergo it because they do not menstruate to begin with. However, biologists generally use the term in a wider sense.

“The term is used in the literature to mean cessation of reproduction, and does not depend on menstruation,” says Simon Chapman at the University of Turku in Finland.

The key physical thing that results from the menopause is the ovaries stop releasing eggs – the oopause. But finding out if and when most mammals undergo oopause is far from easy.

In some species, the presence or absence of reproductive cycles can be directly established by, for instance, looking at hormone levels in blood. But scientists can usually only do such studies in captive animals. And for most species, researchers have to infer the timing of the oopause from when individuals cease reproducing, which is also typically gleaned from animals in captivity.

In their analysis, Winkler and Goncalves looked at studies that included at least 10 captive individuals. While they found reliable studies for less than 100 species, the results showed that the vast majority of these mammals stopped producing eggs if they lived long enough. In fact, female mammals typically underwent the oopause when they were between one-third and two-thirds of the way through their maximum possible lifespan.

“This shows that the [female] reproductive system stops working much earlier than the rest of the body,” Goncalves says. “And for me, it’s absolutely relevant that this happens in other species as well.”

Previous studies have suggested this is the case, Goncalves says, but theirs is the most comprehensive and rigorous analysis so far.

If the menopause is defined as animals undergoing an oopause when they live to a relatively old age rather than being killed by predators or disease, then Goncalves’s study provides good evidence that the menopause is common in many mammals.

But she is not claiming that most wild females survive long enough to undergo the oopause. “It’s not about what’s happening in the wild,” Goncalves says. And what happens in the wild matters from an evolutionary perspective, she says.

“This paper shows nicely that if you’re kept safe from the dangers of the world, eventually you’ll run out of eggs,” says Sam Ellis at the University of Exeter in the UK.

In 2017, his team showed that, in the wild, females from a few species of toothed whale regularly live for significant periods after they are unable to reproduce. His study is the main source for the claim that the menopause occurs only in humans and a handful of whales. But Ellis agrees it depends on which definition you use.

“I deliberately focused on wild populations, and they’ve deliberately focused on captive populations,” he says. “I think both are equally valid. It depends on the kind of question you’re trying to ask.”

Coincidentally, a separate study published the same day described the first evidence for the menopause in wild chimpanzees. There have been occasional reports of individual chimps surviving well past the age they can reproduce. But in one group in the Kibale National Park in Uganda that has been studied for more than 20 years, more than a third of females have been surviving past this point.

However, this particular group has managed to expand its territory – meaning plenty of food – in a region when human hunters have wiped out predators such as leopards. So the observation may be a temporary result of unusually favourable circumstances, rather than the norm, the researchers say. If so, it fits in neatly with both Goncalves’s and Ellis’s findings.

What is clear is that females in the majority of mammal species stop producing eggs long before the end of their maximum potential lifespans, but in the wild few reach this point. Whether this means the menopause is common or rare comes down to how you define it.

SOURCE

Cell DOI: 10.1016/j.cell.2023.09.026


MORE FROM NEWS, VIEWS, AND REVIEWS

  • The Centre for Longitudinal Studies presented findings from more than 50,000 women participating in nine studies worldwide. The results showed women who have never given birth or been pregnant have twice the odds of…

  • Only humans and a few toothed whales undergo the menopause, many sources will tell you. But a paper by Ivana Winkler and Angela Goncalves at the German Cancer Research Center claims that the menopause is, in fact,…

  • In post-menopausal women, the earliest change in the brain appears to be a fall in the amount of glucose used by the brain, indicating reduced brain activity. This is due to falling estrogen levels,…

  • Hot flashes during sleep may be an early marker of a woman’s risk for developing Alzheimer disease (AD), according to the results of a study presented at the 2023 Annual Meeting of the Menopause…

  • In the absence of estradiol, brain glucose transport diminishes significantly. This effectively starves the brain for energy inducing severe bioenergetic deficiencies with all of the concordant neuronal damage one might expect. The reduction in…

  • Women who have used hormone therapy for menopausal symptoms may be more likely to develop gastroesophageal reflux disease, or GERD, a new analysis suggests. The study, published online June 27, 2023, by the journal Menopause,…

  • New Scientist

  • New Scientist

  • New Scientist

  • New York Times

  • New Scientist

  • Guardian

  • Hormones Matter

  • The Guardian

  • Health

VIEW ALL