Menstrual history and bone density in young women.

Adequate levels of reproductive and pituitary hormones are needed for the initiation and maintenance of regular menstrual cycles as well as for the achievement of peak bone mineral density (BMD). Therefore, in the absence of direct hormone measures, menstrual history may serve as a surrogate for the adequacy of hormonal functioning and be a marker for bone status in young women. In our cross-sectional study of white college women aged 19-26 years, we examined the association of six characteristics of menstrual history with bone density at the lumbar spine and the femoral neck. To characterize associations, we used multiple linear regression models that also accounted for the contribution of body mass index, dietary calcium intake, height, level of physical activity, smoking, and alcohol use. The associations between each of the six menstrual characteristics and BMD were stronger at the lumbar spine than at the femoral neck. Age at menarche explained the most variance at both the lumbar spine (partial r2 x 100 = 5.9%) and the femoral neck (partial r2 x 100 = 2.1%). For each year that menarche was delayed, bone density was lower by -0.023 g/cm2 (p = 0.0024) at the lumbar spine and -0.0129 g/cm2 (p = 0.0565) at the femoral neck. At the lumbar spine, a higher number of lifetime menstrual cycles was also significantly associated with increased bone density (adjusted beta = 0.0010, p = 0.0052, partial r2 x 100 = 4.4%). This association was not significant after adjusting for age at menarche. Neither reproductive years (age - age at menarche) nor a history of irregular cycles (either at menarche, in the past year, or ever) was associated with bone density at either site. Menstrual function appears to affect the bone density of these young women. Studies that include measures of reproductive and pituitary hormones are needed to further explore the role of hormones in the potential link between menstrual history and bone density.