Ever wonder if you and your best lady friends will spend your golden years together?

Your period may indicate how long you'll live.

That's the finding in a new study of women conducted by doctors and researchers at the University of California, San Diego.

Most of the women in the study who lived to be 90 had one thing in common: They started their periods at age 12 or older and entered menopause at age 50 or older.

"Not all of them," study author Aladdin Shadyab told ATTN:. "But the majority. We found that among women who survived to age 90, 84 percent of women had their first period at least aged 12 years old."

The study set out to investigate associations between reproductive factors and survival to 90.

It looked at 16,251 women of various ethnic and racial backgrounds from age 69 to 81 and followed them for 21 years. Think "Boyhood," but with older women.

More than half of the women in the study — 55 percent — lived to be 90.

Justin Vidamo/Flickr - flic.kr

So what does this tell us about periods and life spans?

"We observed that women who had their first period aged 12 or older had a 9 percent increased chance of living to age 90," Shadyab said.

Most of the 90-year-old women also began menopause after age 50.

What's the connection between periods, menopause, and longer life?

"Women who started menstruation at a later age were less likely to have certain health issues, like coronary heart disease, and those who experienced menopause later in life were more likely to be in excellent health overall, which may be a possible explanation for our findings," the study found.

The women had one other thing in common: They were drinkers.

Is that a coincidence? "We did not really explore that too much," Shadyab told ATTN:. "That would be for future work."

[H/T Fitness Magazine]