Women keen to know their odds of living to age 90 may find clues in their menstrual history.
In the first-ever study to look at whether reproductive factors predict women's longevity, the chances of surviving nine decades increased for women who hit menopause at age 50 or older, and started their first period at age 12 or later.
The chances of celebrating a 90th birthday were 13 per cent higher in women with more than 40 reproductive years, compared with those with fewer than 33.
The study, published in July in the journal Menopause, involved more than 16,000 participants in the Women's Health Initiative, a U.S. investigation of postmenopausal women, who were followed for 21 years.
The Globe and Mail spoke with the study's lead author, Aladdin Shadyab, a postdoctoral scholar in family medicine and public health at the University of California San Diego.
Your study suggests that women with more reproductive years live longer. Girls are getting their periods earlier and earlier, which should extend their reproductive life. But we're told that's not a good thing.
In our study, the association of age at menarche [first menstrual period] with longevity was a modest association, although it was significant. But the association with age at menopause and reproductive life span with longevity was much stronger. Our findings do fit in with previous studies, which have shown that early menarche [before age 11] is associated with increased risk of adult obesity and diabetes. So it is early menarche that is associated with adverse outcome and it's later menarche that may predict longevity.
Women in this study were born in, or before, 1924. Do these findings apply to women today?
That's a good question. Age at menarche is decreasing, age at menopause is increasing and longevity is increasing all over the world. Younger birth cohorts are needed in follow-up studies to determine whether [the findings] apply to other birth cohorts as well.
Is there any way to delay menopause, and perhaps live longer?
Well, menopause can be caused by several factors: one of them is genetics. Another is smoking, so women who smoke are more likely to experience earlier menopause, which in turn can influence their chances of longevity. Avoiding smoking may lead to a [later] menopause.
Your study found no difference between natural and surgically induced menopause.
That's a very important point to drive home, because it did not matter if a woman had menopause naturally or for surgical reasons. Either way, later menopause predicted higher chances of living to age 90.
What's the best explanation for the link between reproductive years and longevity?We controlled for many variables – including race, ethnicity, marital status and education – and the only thing that explained our findings was self-rated health. Women who had later menopause and later menarche, for whatever reason, are in better health overall. That, in turn, may explain their longevity. But it's important to remember that genetic factors can play a role. There may be a similar set of genes that determine the age at which you have your first period, the age at which you will experience menopause and whether you will live a long life. That is what future studies should determine.