Racial differences in bone density between young adult black and white subjects persist after adjustment for anthropometric, lifestyle, and biochemical differences

This study tested whether racial differences in bone density can be explained by differences in bone metabolism and lifestyle. A cohort of 402 black and white men and women, ages 25-36 yr, was studied at the Kaiser Permanente Medical Care Program in Northern California, a prepaid health plan. Body composition (fat, lean, and bone mineral density) was measured using a Hologic-2000 dual-energy x-ray densitometer. Muscle strength, blood and urine chemistry values related to calcium metabolism, bone turnover, growth factors, and level of sex and adrenal hormones were also measured. Medical history, physical activity, and lifestyle were assessed. Statistical analyses using t- and chi-square tests and multiple regression were done to determine whether racial difference in bone density remained after adjustment for covariates. Bone density at all skeletal sites was statistically significantly greater in black than in white subjects; on average, adjustment for covariates reduced the percentage density differences by 42% for men and 34% for women. Adjusted bone density at various skeletal sites was 4.5-16.1% higher for black than for white men and was 1.2-7.3% higher for black than for white women. We concluded that racial differences in bone mineral density are not accounted for by clinical or biochemical variables measured in early adulthood.