Impact of obesity on bone mass throughout adult life: Influence of gender and severity of obesity

Background: Obesity improves areal bone mineral density (aBMD). However, it is unknown whether gender, ageing or the severity of obesity could modulate this effect and whether different bone sites are similarly affected. Objective: The aim of this observational study was to model the aBMD variation in obese patients from peak bone period to old age according to gender, bone localisation and severity of obesity. Subjects and methods: Five hundred and four obese patients (363 women, 72%) with a mean BMI of 38.5 +/- 6.0 kg/m(2), aged from 18.1 to 81.9 years (mean age 49.6 +/- 14.6 years) were recruited. The whole body (WB), hip, lumbar spine (L1-L4) and one-third radius aBMDs were determined using dual-energy x-ray absorptiometry (DXA). Results: Z-scores were significantly increased, above the age- and gender-related mean, both for women and men at WB (respectively 0.79 SD and 0.32 SD), hip (1.09 SD and 1.06 SD), one-third radius (1.70 SD and 0.45 SD) and L1-L4 levels (0.86 SD for women only). The improvement of Z-scores was significantly more marked in women compared to men at all bone sites, hip excepted. Furthermore, differences compared with normal values were significantly accentuated by ageing, without noticeable gender effect. In women, regardless of BMI and bone site, Z-scores were higher than normal values, this difference being most marked at WB, L1-L4 and hip levels for obese patients with a BMI above 40 kg/m(2). Lean mass, but not fat mass, was independently associated with aBMD in men and women. Conclusion: This study demonstrated for the first time that obesity induces an improvement of aBMD, which is modulated by bone site location, severity of obesity, age and gender. The accentuation of peak bone mass combined with a reduction of bone loss rate with ageing may explain why obese patients present a lower prevalence of osteoporosis. (C) 2015 Elsevier Inc. All rights reserved.