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

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.

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.

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.

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.