Analysis of body composition in individuals with high bone mass reveals a marked increase in fat mass in women but not men

Gregson, C.L., Paggiosi, M.A., Crabtree, N., Steel, S.A., McCloskey, E., Duncan, E.L., Fan, B., Shepherd, J.A., Fraser, W.D., Smith, G.D. and Tobias, J.H. (2013) Analysis of body composition in individuals with high bone mass reveals a marked increase in fat mass in women but not men. Journal of Clinical Endocrinology & Metabolism, 98 (2), 818-828. (doi:10.1210/jc.2012-3342). (PMID:23337721)

Abstract

CONTEXT: High bone mass (HBM), detected in 0.2% of dual-energy x-ray absorptiometry (DXA) scans, is characterized by raised body mass index, the basis for which is unclear.

OBJECTIVE: To investigate why body mass index is elevated in individuals with HBM, we characterized body composition and examined whether differences could be explained by bone phenotypes, eg, bone mass and/or bone turnover.

DESIGN, SETTING, AND PARTICIPANTS: We conducted a case-control study of 153 cases with unexplained HBM recruited from 4 UK centers by screening 219 088 DXA scans. A total of 138 first-degree relatives (of whom 51 had HBM) and 39 spouses were also recruited. Unaffected individuals served as controls.

MAIN OUTCOME MEASURES: We measured fat mass, by DXA, and bone turnover markers.

RESULTS: Among women, fat mass was inversely related to age in controls (P = .01), but not in HBM cases (P = .96) in whom mean fat mass was 8.9 [95% CI 4.7, 13.0] kg higher compared with controls (fully adjusted mean difference, P < .001). Increased fat mass in male HBM cases was less marked (gender interaction P = .03). Compared with controls, lean mass was also increased in female HBM cases (by 3.3 [1.2, 5.4] kg; P < .002); however, lean mass increases were less marked than fat mass increases, resulting in 4.5% lower percentage lean mass in HBM cases (P < .001). Osteocalcin was also lower in female HBM cases compared with controls (by 2.8 [0.1, 5.5] ?g/L; P = .04). Differences in fat mass were fully attenuated after hip bone mineral density (BMD) adjustment (P = .52) but unchanged after adjustment for bone turnover (P < .001), whereas the greater hip BMD in female HBM cases was minimally attenuated by fat mass adjustment (P < .001).

CONCLUSIONS: HBM is characterized by a marked increase in fat mass in females, statistically explained by their greater BMD, but not by markers of bone turnover.

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