Menopause is a natural and inevitable part of getting older for people born with ovaries.
It marks the end of a woman's reproductive years, and is associated with a range of changes including bone thinning, weight gain and bladder issues.
A new study, in Nature Medicine today, suggests the biological changes across multiple body systems are not gradual, but sudden and "cliff-like".
To reach this conclusion, researchers analysed more than 300 million laboratory tests from more than 1 million women in the United States and Israel between 1999 and 2024.
The study, led by Uri Alon, head of the Sagol Center for Longevity Research at Israel's Weizmann Institute, found "abrupt, step-like changes across nearly all physiological systems" at menopause.
But Australian experts urge caution interpreting the results.
Martha Hickey, head of menopause services at The Women's Hospital Victoria who was not involved in the study, described the claim of "cliff-like" changes across multiple body systems as "unnecessarily alarming" for women.
"Physiological cliff is not a scientific or medical term," she said.
Menopause is a time 12 months after a person's last period when their ovaries stop functioning.
During menopause a woman's body undergoes changes affecting the heart, skin, brain, bones and reproductive system, primarily because much lower amounts of oestrogen and progesterone are being produced.
Highly respected studies, such as the long-running US Study of Women's Health Across the Nation (SWAN), suggests these all-body changes are gradual, happening over about three years.
But the new study challenges this concept.
"Our study used a mathematical approach to align large-scale data at the final menstrual period, and therefore had more data and more advanced analysis than SWAN," Professor Alon said.
"That is why we could pick up the cliff.
"We verified the [cliff] is real because applying our approach to men showed no cliff, and we also tested it using a vast range of simulated data and comparison to specific experimental data."
This change was found in the body's sex hormones, bone health, liver and kidney function, blood chemistry, and blood fats.
While the SWAN study was designed to follow women's health over the menopause transition, the new study used existing data and relied on self-reported information about a woman's last period.
Professor Hickey said retrospective studies were "poor quality" and were not designed to answer the question posed in this case.
Sydney-based general practitioner Elina Safro, who chairs the education subcommittee of the Australasian Menopause Society, agreed.
"My reading is that the 'cliff' theory is not plausible," she said.
Despite skepticism from Australian experts about the "cliff-like" decline, there were parts of the study they said were worth highlighting.
One was that accelerated change across many of the body's systems began about 15 years prior to menopause.
This, Dr Safro said, was about seven years earlier than indicated in the SWAN study and indicated the importance of remaining vigilant about health in midlife, particularly in women.
The study also indicated that sudden changes were smaller for women taking menopausal hormone therapy (MHT), particularly regarding bone, liver and kidney function.
Professor Alon said many people started taking MHT a year after their final menstrual period, but his study suggested taking it earlier could help maintain bone health.
"Nowadays people check bone density around age 60, but this study would advocate checking around age 40 or 45 and then considering menopausal hormone therapy as prevention," he said.
"Of course we don't want to over treat, so this has to be done on the advice of a physician."
While there was good evidence MRT could reduce the risk of osteoporosis and broken bones, Professor Hickey said there was no evidence to suggest it would help prevent chronic conditions such as cardiovascular disease and dementia.
She also said that healthier women were more likely to use MHT, which suggested there could be pre-existing differences between the study's participants taking it and the rest of the group.
While menopause is an inevitable part of aging for people with ovaries, there are some things that may ease the severity of symptoms, such as quitting smoking, limiting alcohol consumption, eating well and remaining physically active.
University of Melbourne endocrinologist Ada Cheung, who did not contribute to the study, said it showed "health checks matter around menopause".
"Menopause is natural, but that doesn't mean you have to just put up with it.
"Your body goes through real, measurable changes, and that's not 'in your head.'"
Professor Cheung recommended women speak to their GP in their 40s, about symptoms, bone and heart health, and whether hormone therapy was right for them.
All four experts agreed more research was needed.
Professor Alon said his team were planning a clinical trial to evaluate outcomes for people who took MHT before their period ended and menopause started.
He hoped this would help provide evidence for better treatment options.
