There is conflicting evidence concerning an association between early menarche (the onset of menstruation) and the development of type 2 diabetes later in life, which is further complicated by questions about the impact of body mass index (BMI) on both. To evaluate this relationship, researchers analyzed data from InterAct, a prospective cohort study of more than 27,500 patients from eight European countries (InterAct is itself nested within a much larger study). From among InterAct's numbers, 6,238 women with type 2 diabetes were included in the study; a representative subcohort of 10,043 women was chosen for comparison.

In both groups, age at menarche was normally distributed, with a mean age of 13 years. Among women with early menarche, defined as menarche occurring between the ages of eight and 11, there were 4.3 cases of type 2 diabetes per 1,000 person years, compared with 2.9 cases among those in whom menarche occurred at the age of 13. A separate model that broke the age at menarche into five almost evenly divided categories-eight to 11, 12, 13, 14, and 15 to 18-revealed a 70% higher risk of diabetes among those in the early menarche group. With each later year at which menarche occurred, the risk decreased by 9%, except among women who experienced menarche between ages 15 and 18, in whom no protective effect was seen.

When the authors adjusted for adult BMI, the hazard ratio for type 2 diabetes in the early menarche group was reduced from 1.7 to 1.4. Results were similar after adjustment for waist circumference.

The authors conclude that because higher adult BMI could account for less than half of the increase in diabetes risk, early menarche increased the risk of diabetes by 42%. They write, "Although avoidance of adult overweight and obesity may attenuate the risk of type 2 diabetes in women with early menarche, our findings suggest that strategies to prevent early menarche may be important in their own right."

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