A large new study says the body changes in a sudden way at menopause, not slowly over years. The study was published in Nature Medicine, ABC News in Australia and Scientific American reported.

The team looked at more than 300 million lab tests from more than 1 million women in the United States and Israel, ABC reported. The tests ran from 1999 to 2024. The study was led by Uri Alon of Israel's Weizmann Institute.

The researchers found sudden jumps in tests for bone, liver, kidney, blood chemistry and blood fats. "Menopause is not a slow part of aging," Alon told Scientific American. Some jumps were good, such as in iron and hemoglobin, likely because monthly bleeding stops, he said.

The team checked the result in men of the same ages and saw no jumps. Women on hormone therapy had smaller jumps, "especially in bone, liver and kidney," Alon said. He told ABC that the study would support checking bone density around age 40 or 45.

Not everyone agrees. Martha Hickey, who runs menopause services at The Women's Hospital Victoria, called the cliff claim "unnecessarily alarming" for women. "Physiological cliff is not a scientific or medical term," she told ABC. She said the study used older records and was not built to answer this question. Earlier work, such as the U.S. SWAN study, found the changes happen over about three years.

Experts did point to one useful finding. Faster change across many body systems began about 15 years before menopause, ABC reported.

What we know: A study of more than 1 million women found sudden lab changes at menopause, and they were smaller with hormone therapy.
What we don't: Whether the changes are truly sudden, and whether starting hormone therapy earlier would help.