Long or highly irregular menstrual cycles as a marker for risk of type 2 diabetes mellitus

Context Although oligomenorrhea has been associated cross-sectionally with insulin resistance and glucose intolerance, it is not known whether oligome norrhea is a marker for increased future risk of type 2 diabetes mellitus ( DM). Objective To prospectively assess risk of type 2 DM in women with a history of long or highly irregular menstrual cycles. Design and Setting The Nurses' Health Study II, a prospective observational cohort study. Participants A total of 101073 women who had no. prior history of DM and wh o reported their usual menstrual cycle pattern at age 18 to 22 years on the baseline (1989) questionnaire. Main Outcome Measure Incident reports of DM, with follow-up through 1997, c ompared among women categorized by menstrual cycle length (5 categories). Results During 564333 person-years of follow-up, there were 507 cases of ty pe 2 DM. Compared with women with a usual cycle length of 26 to 31 days (re ferent category) at age 18 to 22 years, the relative risk (RR) of type 2 DM among women with a menstrual cycle length that was 40 days or more or was too irregular to estimate was 2.08 (95% confidence interval [CI], 1.62-2.66 ), adjusting for body mass index at age 18 years and several other potentia l confounding variables. The RR of type 2 DM associated with long or highly irregular menstrual cycles was greater in obese women, but was also increa sed in nonobese women (at body mass indexes at age 18 years of <25,25-29, a nd <greater than or equal to>30 kg/m(2), RRs were 1.67 [95% CI, 1.14-2.45], 1.74 [95% CI, 1.07-2.82], and 3.86 [95% CI, 2.33-6.38], respectively). Conclusion Women with long or highly irregular menstrual cycles have a sign ificantly increased risk for developing type 2 DM that is not completely ex plained by obesity.