Ovarian aging and bone metabolism in menstruating women aged 35-50 years.

Objectives: The aim of this study was to investigate the relationships between the levels of gonadotrophins, estradiol, inhibin-b and bone mass and turn-over in regularly menstruating women aged 35-50 years.

Methods: The study group included 87 healthy volunteers from the community aged 35-50 years. Bone mineral density of lumbar vertebras, wards triangle, throchanter, femur neck, bone resorption and formation markers were studied as well as the serum levels of gonadotrophins, estradiol and inhibin-b on the day 3 of menstrual cycle.

Results: The gonadotrophin levels showed significant positive relation with age, whereas inhibin-b and estradiol levels showed significant negative correlation with age. The gonadotrophins and estradiol levels had no significant association with bone mass and bone formation markers. Increased gonadotrophin (p < 0.001) levels and decreased inhibin-b (p < 0.01) levels independent from age were correlated with increased bone resorption. Gonadotrophins, estradiol, age, inhibin-b, body mass index (BMI) were the confounding factors for bone resorption (p = 0.015, R(2) = 0.190) and lumbar bone mass (p = 0.041, R(2) = 0.148). Multivariate analysis showed an independent contribution of inhibin-b and BMI in the prediction of lumbar bone mass.

Conclusion: This findings suggested that estradiol was not the only factor responsible for bone loss and decrease in reproductive function because increased gonadotrophins and decreased inhibin-b levels might trigger some changes in bone metabolism prior to the menopause.