Overweight children have a greater proportion of fat mass relative to muscle mass in the upper limbs than in the lower limbs: implications for bone strength at the distal forearm

• Published in: The American journal of clinical nutrition 2009-10, Vol.90 (4), p.1104-1111
• Main Authors: Ducher, Gaele, Bass, Shona L, Naughton, Geraldine A, Eser, Prisca, Telford, Richard D, Daly, Robin M
• Format: Article
• Language: English
• Subjects: Adiposity; arms (limbs); Biological and medical sciences; body fat; Bone Density; bone fractures; bone mineral content; bone strength; boys; Child; children; Childrens health; computed tomography; Diet; Feeding. Feeding behavior; Female; Forearm - physiopathology; Fundamental and applied biological sciences. Psychology; Humans; legs; limb bones; Lower Extremity - physiopathology; Male; Mechanical Phenomena; muscle tissues; Muscle, Skeletal - physiopathology; Musculoskeletal system; Nutrition; Obesity; overweight; Overweight - physiopathology; Radius - physiopathology; Tibia - physiopathology; Tomography, X-Ray Computed; Upper Extremity - physiopathology; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0002-9165; 1938-3207
• DOI: 10.3945/ajcn.2009.28025

BACKGROUND: The influence of adiposity on upper-limb bone strength has rarely been studied in children, despite the high incidence of forearm fractures in this population. OBJECTIVE: The objective was to compare the influence of muscle and fat tissues on bone strength between the upper and lower limbs in prepubertal children. DESIGN: Bone mineral content, total bone cross-sectional area, cortical bone area (CoA), cortical thickness (CoTh) at the radius and tibia (4% and 66%, respectively), trabecular density (TrD), bone strength index (4% sites), cortical density (CoD), stress-strain index, and muscle and fat areas (66% sites) were measured by using peripheral quantitative computed tomography in 427 children (206 boys) aged 7-10 y. RESULTS: Overweight children (n = 93) had greater values for bone variables (0.3-1.3 SD; P < 0.0001) than did their normal-weight peers, except for CoD 66% and CoTh 4%. The between-group differences were 21-87% greater at the tibia than at the radius. After adjustment for muscle cross-sectional area, TrD 4%, bone mineral content, CoA, and CoTh 66% at the tibia remained greater in overweight children, whereas at the distal radius total bone cross-sectional area and CoTh were smaller in overweight children (P < 0.05). Overweight children had a greater fat-muscle ratio than did normal-weight children, particularly in the forearm (92 ± 28% compared with 57 ± 17%). Fat-muscle ratio correlated negatively with all bone variables, except for TrD and CoD, after adjustment for body weight (r = -0.17 to -0.54; P < 0.0001). CONCLUSIONS: Overweight children had stronger bones than did their normal-weight peers, largely because of greater muscle size. However, the overweight children had a high proportion of fat relative to muscle in the forearm, which is associated with reduced bone strength.