Forever Follicles

from WIRED

ILLUSTRATION: KATERYNA KON/GETTY IMAGES

THE OVARY IS a time machine. It travels to the future, reaching old age ahead of the rest of the body. At birth, each ovary contains around a million follicles—tiny, fluid-filled sacs that hold immature eggs. But the decline of these follicles is immediate and unceasing. By puberty, only about 300,000 remain. By age 40, the vast majority are gone. And by 51, the average age of menopause in the United States, virtually none are left. 

Humans are an oddity in this regard. Most mammals remain fertile up to the end of their lives; the only species known to experience menopause naturally are humans and some whales. In humans, the loss of hormones during menopause sets off a cascade of negative health effects: Bones get brittle; metabolism slows; and the risk of cardiovascular disease, diabetes, stroke, and dementia increases. Paradoxically, women live longer than men on average but spend more of their older years in poor health. 

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