JOURNAL OF BONE AND MINERAL zyxwvuts RESEARCH Volume 8, Number zyxwvutsrq 5,1993 zyxwvutsrqpo Mary Ann Llebert, lac., Publishers Effects of Weight and Body Mass Index on Bone Mineral Density in Men and Women: The Framingham Study DAVID T. FELSON, YUQING ZHANG, MARIAN T. HANNAN, and JENNIFER J. ANDERSON ABSTRACT We evaluated the association of weight and bone mass in elderly male and female subjects of the Framing- ham osteoporosis study, a subset of the Framingham study cohort. By examining the differences in the cor- relations of weight with bone mass among men and women in weight-bearing and non-weight-bearing sites and weight change since early adulthood, we attempted to understand different ways in which weight or body mass index affects bone mass. During biennial examination 20 of the Framingham cohort (1988-1989), 693 women and 439 men (mean age 76 years) had proximal femur bone mineral density assessed by dual- photon absorptiometry (DPA) and radius bone mass zyxwv assessed by single-photon absorptiometry. The major- ity of these subjects also had spine measurements by DPA. Subjects had been weighed repeatedly over 40 years. After adjusting for other factors affecting bone density, we found that both recent weight and body mass index explained a substantial proportion of the variance in bone mineral density for all sites in women (8.9-19.8% of total variance, all zyxwvutsr p zyxwvut < 0.01) and for only weight-bearing sites (femur and spine) in men (2.8- 6.9% of total variance, all p < 0.01). For bone mineral density at the proximal radius, weight and body mass index accounted for <1% of variance in men (p NS). Weight change since biennial examination 1 (1948-1951) was the strongest explanatory factor for bone mineral density among women at all sites, but weight change did not affect radius bone mineral density in men. The effect of weight and of weight change on bone mineral density was in general much less in men than in women. Our results suggest that the strong effect of weight on bone mineral density is due to load on weight-bearing bones in both sexes. The sex differ- ence is unexplained but may be due to adipose tissue production of estrogen in women after menopause. INTRODUCTION HE RELATIONSHIP between weight and bone mineral T density is well established. Cross-sectional studies have shown convincingly that body weight correlates with bone mineral density in and w~rnen.~~-’) The relation- ship between body weight and bone mineral density may be even stronger than the relationship between age and bone mineral density. 113m Both weight and adiposity could affect bone mineral density in at least three ways, each of which has been pos- tulated to be important. First, heavy persons subject their weight-beraring bones to more load than thin persons. Sec- ond, weight in early adulthood could affect peak bone mineral density. Third, in postmenopausal women, adi- pose tissue serves as the site of conversion of androstened- ione to the metabolically active estrogen, estrone. provid- ing obese postmenpausal women with higher circulating endogenous estrogen levels than nonobese women. The third mechanism may explain why obese women do not lose bone as rapidly as nonobese women just after the menopause. w’) Other explanations for the effect of weight on bone are also possible. We measured bone mineral density in Framingham co- hort subjects during the 20th biennial examination (1988- 1989). Since we assessed weight-bearing and non-weight- bearing sites in both sexes, we were able to contrast the ef- fect of load on weight-bearing bones (proximal femur and - Boston University Arthritis Center and the Departments of Medicine at Boston City Hospital and University Hospital, Boston. 567