BODY-SIZE AND HIP FRACTURE RISK IN OLDER WOMEN - A PROSPECTIVE-STUDY

PURPOSE: TO determine the relationship between measures of body size a nd the risk of hip fracture in elderly women. PARTICIPANTS AND METHODS : The association between measures of body size and hip fracture risk was assessed in 8,011 ambulatory, nonblack women 65 years of age or ol der enrolled in the Study of Osteoporotic Fractures with measurements of total body weight, percent weight change since age 25, hip girth, l ean mass, fat mass, percent body fat, body mass index, modified body m ass index, and femoral neck bone mineral density (BMD) at the second e xamination. These 8,011 women were followed prospectively for incident hip fractures occurring after the second examination, which were conf irmed by review of x-ray films. RESULTS: During an average of 5.2 year s after the second examination, 236 (2.9%) women experienced hip fract ures. Similar associations were observed between hip fracture risk and all measures of body size including total body weight, percent weight change since age 25, hip girth, lean mass, fat mass, percent body fat , body mass index, and modified body mass index. Women with smaller bo dy size had a higher risk of subsequent hip fracture compared with tho se with larger body size, while women with average and larger body siz es shared similarly lower risks of subsequent hip fracture. For exampl e, the incidence rate of hip fracture was 9.35 per 1000 woman-years in women in the lowest quartile of total weight compared with 4.63 per 1 000 woman-years in women in the highest quartile of total weight (age- adjusted relative risk 1.93, 95% confidence interval (CI) 1.34 to 2.80 ), while rates of hip fracture among women in the second and third qua rtiles of total weight (5.22 and 4.32 per 1000 woman-years, respective ly) were not significantly different from the rate among women in the highest quartile (P > 0.64). The increased risk of hip fracture among women of smaller body size remained after further adjustment for addit ional potential confounding factors including height at age 25, smokin g status, physical activity, health status, estrogen use, and diuretic use. After further adjustment for femoral neck BMD, women with smalle r body size were no longer at significantly increased risk of hip frac ture compared with those with larger body size. For example, after adj ustment for height at age 25, smoking status, physical activity, healt h status, estrogen use, and diuretic use, thin women had a 2.5-fold in crease in the risk of hip fracture (multivariate relative risk 2.51, 9 5% CI 1.69 to 3.73) compared with the referent group composed of the h eaviest women. After further adjustment for femoral neck BMD, the mult ivariate relative risk of hip fracture among thin women compared to he aviest women was 0.98 (95% CI, 0.64 to 1.50). CONCLUSION: Older women with smaller body size are at increased risk of hip fracture. This eff ect is because of lower hip BMD in women with smaller body size. Asses sment of body size for prediction of hip fracture risk can be accompli shed by measuring total body weight. (C) 1997 by Excerpta Medica, Inc.