Bone mass, bone metabolism, gonadal status and body mass index

Weight and gonadal status are the main determinants of bone mass in women. Because of this it is important to study which influences it more. The effect of weight (expressed as body mass index, BMI) and gonadal status of women on total-body bone mineral content (TBBMC) and regional bone mineral content (BMC) was investigated. A total of 373 normal women (mean age 48.9 +/- 13.4 years) were studied: 171 postmenopausal women (mean age 59.3 +/- 9.5 years; years since menopause 11.3 +/- 6.7 years); 76 perimenopausal women (mean age 48.9 +/- 2.2 years); and 126 premenopausal women (mean age 34.7 +/- 7.4 years). In all the women, TBBMC and regional BMC were determined by dual-energy X-ray absorptiometry. Also biochemical markers of bone metabolism (total alkaline phosphatase and tartrate-resistant acid phosphatase) and serum estrone and estradiol were determined. When the women were stratified by gonadal status and BMI, thin women (BMI <20 kg/m2) had significantly lower TBBMC and regional BMC, lower gonadal steroid concentration and higher levels of biochemical markers than overweight (BMI 25-30 kg/m2) and obese (BMI >30 kg/m2) women, regardless of gonadal status. Overweight and obese women had findings suggestive of increased parathyroid activity, but greater bone mass. Weight rather than gonadal steroid concentration is the main determinant of bone mass in women regardless of gonadal status.