Body fat mass is a predictor of risk of osteoporotic fractures in women but not in men: a prospective population study

Moayyeri A, Luben RN, Wareham NJ, Khaw K-T (University of Cambridge, Cambridge; Institute of Metabolic Science; Cambridge, UK). Body fat mass is a predictor of risk of osteoporotic fractures in women but not in men: a prospective population study. J Intern Med 2012; 271: 472480. Objectives. Obesity has generally been associated with higher bone density and lower fracture risk. However, weight-related indices of obesity may be related differently to health end-points, compared with fat-related indices (such as body fat distribution and fat mass), as they may capture different dimensions of obesity and the associated biological effects. The aim of this study was to examine the association between percentage body fat (%BF) and prospective risk of fracture. Methods. The European Prospective Investigation into Cancer (EPIC) in Norfolk was a population-based prospective study. A total of 14 789 participants (6470 men, aged 4282 years at baseline) were included. The main outcome measures were quantitative ultrasound of the heel and incident hip and any osteoporotic fractures. Results. A total of 556 participants suffered a fracture (184 hip fractures) during 8.7 +/- 0.8 years of follow-up. Risk of hip fracture decreased linearly with increasing %BF amongst women but not men. After adjustment for age, history of fracture, height, smoking, alcohol intake and heel broadband ultrasound attenuation (BUA), the hazard ratio (95% CI) for a 10% higher %BF on risk of hip fracture was 0.56 (0.390.79) in women and 0.92 (0.392.21) in men. The effect size in women was approximately equivalent to a difference of 5 years in age or 1 standard deviation (17 dB MHz-1) increased BUA. A nonlinear negative association was also observed between %BF and risk of any type of fracture amongst women but not men. Conclusions. The %BF appears to predict hip fracture risk in women with an effect size comparable to that of bone density as measured by heel ultrasound. This effect was not observed in men. Understanding the differences in relationships between different indices of obesity as well as sex differences may help to elucidate the metabolic and other underlying mechanisms involved in bone health and fracture risk.