Study of Total Bone Mineral Density, Fat Mass and Lean Body Mass in Healthy Japanese Children

In Japanese children, we measured total body bone mineral content (TBMC), total body fat (TBF) and total body lean (TBL) in 59 in elementary school, 83 in junior high school and 51 in high school, by dual energy X-ray absorptiometry (DEX ODR-2000). The objective of the study was to clarify body composition including bone mineral content (BMC), fat mass and lean mass at various ages, and the relationship between BMC and fat or lean. Lumbar bone mineral density (L2-L4 BMD; g/cm2) was also calculated from the BMC (g) and area (cm2). TBF in girls and TBL in boys increased significantly at age 12 years, although TBMC was similar in both sexes. The ratios of TBMC, TBF and TBL at age 18 years were 5.7%, 13.8% and 80.5% in males, and 8.0%, 26% and 66% in females, respectively. BMC in the extremities increased with lean body mass from age 10 years in boys, and spinal and pelvic BMC increased with the fat mass of the trunk from age 10 years in girls. In girls, TBMC was significantly related to lean in the trunk (r=0.325; p<0.01), independently of age, height and weight. In both sexes, TBMC was significantly negative related to fat in the trunk (girls: r=-0.305; p<0.01, boys: r=-0.537; p<0.01), independently of age, height and weight.