Menstrual irregularity is associated with higher bone mass in young women which is mediated through alterations in endogenous androgens

Abstract

Background: There have been few studies examining the association between menstrual irregularity, androgens and bone mineral density in premenopausal women. Objective: To describe the association between menstrual irregularity, androgens and bone mass measured by quantitative ultrasound (QUS) in premenopausal women who were not taking hormonal contraceptives. Methods: Australia wide cross-sectional study (N=382, mean age 31 years). Menstrual irregularity was assessed based on selfadministered questionnaire. Bone mass was measured by Hologic Sahara densitometer. Total testosterone and SHBG were assessed by fasting blood sample and free androgen index was derived. Results: Women with irregular cycles (n=41, 11%) had higher SOS and QUI (median difference 6 m/s and 7.2% respectively, p<0.05) and a trend to higher BUA (5.1 dB/MHz, p=0.10). These associations persisted after adjustment for ambient temperature, age, BMI and smoking. Total testosterone, free androgen index and SHBG were associated with all QUS measures (testosterone and FAI r +0.11 to +0.21, all p<0.05; SHBG r −0.14 to −0.16, all p<0.05) and the associations remained significant after adjustment. However, the associations between menstrual irregularity and QUS were partially attenuated after adjustment for hormonal factors especially FAI becoming non significant at all sites. Conclusion: In our increasingly obesogenic society, irregular cycles are now associated with higher bone mass in a populationbased sample of premenopausal women. The association between menstrual irregularity and bone mass is, at least, partially mediated by free testosterone while total testosterone, FAI, and SHBG are independently associated with bone mass.