Girls get their first period anytime between the ages of 8 and 15. In the US, the average age for a girl to start menstruating is 12 – and that’s bad news according to the latest research by Tohoku University and Teikyo University School of Medicine.

Women who start getting their periods at age 13 or earlier are about 1.8 times more likely to suffer a stroke than women who begin at age 15. Their later-blooming counterparts are also less likely to suffer from a cerebral infarction – that’s the condition where a section of brain tissue dies as a reduced blood flow and oxygen. The scientists also deduced that women who stopped menstruating at 45 or younger are more likely to get cerebral infarction, but not stroke, compared to women who began menopause at the age of 50.

All of these stats play into a grander thesis upholding that a woman’s menarche and menopause – the ages when she starts and stops having her periods, respectively – factor into other diseases. Whether there is direct causation, or merely prediction, there is no doubt that understanding the connection better will lead to more effective measures of prevention.

The Japanese team examined data produced by a group of 1,412 post-menopausal women in the rural town of Ohasama, Japan, between 1998 and 2010. They tracked the women's ages of menarche and menopause, if and when they had a stroke, and other health factors such as weight, height, high blood pressure and heart disease. The researchers found a statistically significant link between between stroke risk and early menarche, but not between stroke mortality and menarche.

We do know that the onset of menstruation is affected by many factors, including socioeconomic and behavioral influences. Scientists are currently looking into what impact if any delaying menarche might have on stroke prevention. The current research has only been done with girls living in rural areas, and other data indicate that girls in developed nations are starting their periods earlier.

The study was published in Neuroepidemiology.