Women who had their first menstrual period at a younger-than-average age may live shorter lives than their peers, the results of a new study suggest.
In a long-term study of more than 61 000 Norwegian women, researchers found that those who began menstruating at a relatively young age - 12 or younger - had a slightly higher risk of dying during the study period.
10% increased risk
Among women who had their first period at the age of 10 or 11, the risk of death was roughly 10 percent higher than that of women who began menstruating at age 14 - the average for the study group.
In contrast, women who had their first period at age 15 or older had a lower risk of dying during the study period, the researchers report in the American Journal of Epidemiology.
The reasons for the findings are not certain, according to the investigators, led by Dr Bjarne K. Jacobsen of the University of Tromso.
Certain factors that the study did not assess - such as exercise or smoking - might be at work, they point out. For example, intense physical activity is known to delay or disrupt the menstrual cycle, and regular exercise over a lifetime can help prevent chronic ills like diabetes and heart disease.
Higher breast cancer risk
On the other hand, studies have linked earlier menarche (the term for the first menstrual period) to a higher long-term risk of breast cancer, Jacobsen told Reuters Health. It's thought that this risk may arise from greater lifetime exposure to oestrogen.
"However," Jacobsen pointed out, "breast cancer is not the most important cause of death in women."
It's also possible, the researcher speculated, that a later menstruation reflects a woman's being "biologically younger" than her actual age.
"We have already found that a late menopause is associated with reduced total mortality," Jacobsen explained, "and this fits into the picture that women who are biologically younger than their chronological age...tend to live longer."
The current findings are based on a 37-year follow-up study of 61 319 women born between the late 1800s and the 1920s. Beginning in the 1950s, the women were examined by a doctor and questioned about their reproductive history, including their age at their first period.
Jacobsen's team found that even with factors such as weight and socioeconomic status considered, the risk of death was generally lower among women with a later menarche. The link was stronger among study participants who were younger than 70 compared with older women.
Periods starting earlier
Studies have shown that girls in Western countries are starting their periods earlier than they once were. In the US, the average age is now 12. Researchers believe that the reason at least partially rests in the growing ranks of overweight and obese children; body fat helps trigger and maintain regular menstrual periods.
However, while the current findings suggest that earlier menarche is linked to a shorter lifespan across a large population, the effect on any one woman would be of "minor importance", according to Jacobsen.
"The age at menarche," the researcher stressed, "is something a girl should not try to influence - for example, by eating too little or training too hard."
SOURCE: American Journal of Epidemiology, December 15, 2007. – (Reuters Health)
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