Factors associated with the rise and fall of bone mineral density in reproductive-age women: Data from the 5th Korea National Health and Nutrition Examination Survey

Purpose: According to previous study, the patterns of age-related bone mineral density (BMD) of femur and spine in reproductive-age women showed marked ups and downs after reaching peak BMD than those of men. We investigated the factors which are associated with this BMD change using nonlinear models.

Materials and methods: A total of 4681 women recruited during the 5^th Korean National Health and Nutrition Examination Survey 2010-2011 (KNHANES V) were included. Multiple factors such as lean body mass, drinking/smoking, degree of exercise, age at menarche, age at first delivery, total number of delivery, history of breastfeeding, age at menopause and presence of hormone therapy/diabetes were adjusted. The trend of age-related BMD change was demonstrated using generalized additive model (GAM) with smoothing spline transformation.

Result: The simple and GAM plot of BMD according to age revealed two peaks in total femur, femoral neck and lumbar spine. After adjustment for lean body mass (LBM), the peaks were changed to be more flattened. In the model including all the covariates, the pattern of BMD according to age showed single peak around age of 40. Age, LBM, age at menarche and history of breastfeeding were common significant predictors in BMD in multiple regression models for BMD of total femur, femoral neck  and lumbar spine.

Conclusion: Using nonlinear model, the up and down change in BMD of reproductive-age Korean women could be largely attributed by the factors including LBM, age at menarche and history of breastfeeding.