Abstract
Black adults have higher bone mass than whites in the United States, but it is not clear when black children gain bone mineral faster than white children. We performed a cohort study to compare the growth velocity of total-body bone mineral content (TBMC) between black and white children of the same sex at different ages and stages of sexual maturity. TBMC and total-body area were measured in a cohort of 188 black and white boys and girls aged 5 to 15 years annually for up to 4 years. Rates of change in TBMC and area were found to vary with age and with Tanner stage. For both TBMC and area, growth velocities between black and white children differed significantly across Tanner stages. Age-specific velocities were higher in black children during prepuberty and initial entry into puberty but reversed in subsequent Tanner stages. Despite earlier entry into each Tanner stage, black children spent only an average of only 0.2 year longer in Tanner stages II through IV, and total gain in TBMC from age 5 to 15 was not higher in whites. In conclusion, the higher bone mass in black adults compared with whites cannot be attributed to faster accrual during puberty. It is due to black children's higher rate of bone mineral accrual in prepuberty and plausibly in postpuberty. Most of the racial difference in TBMC velocity can be explained by growth in size. © 2010 American Society for Bone and Mineral Research.
Highlights
Our population mean curves of total-body bone mineral content (TBMC) and TAREA (Figs. 1 and 2, top panels) agree with all earlier studies that have shown that black children have higher bone mass than white children of the same sex at all ages.[3,9,11,12,13,14] Previous studies have found an association between higher peak bone mass and earlier puberty,(21–24) through longer exposure to sex hormones during puberty, as suggested by some.[25,26,27] Since black children, on average, have earlier puberty than white children, we hypothesized that blacks would have faster bone growth rates and greater total bone accrual than whites during puberty
Our findings suggest that higher peak bone mass in blacks observed in all studies of adults is not due to earlier puberty or faster bone growth in puberty but is at least partially attributable to their faster bone accrual during the prepubertal years
Two other longitudinal studies have compared the growth of TBMC between black and white children
Summary
African Americans have higher bone mass and lower fracture rates than European Americans of the same sex and age.[1,2] The higher bone mass in older black adults is a result of their higher peak bone mass in early adulthood[3,4,5] and lower rates of loss with aging.[6,7] The racial difference in bone mineral content (BMC) and areal bone mineral density (aBMD 1⁄4 BMC/area), though not apparent in infancy,(8) emerges by early childhood and persists through adolescence and young adulthood.[3,8,9,10,11,12,13,14] It is unclear, when the greatest difference in the rate of skeletal mineral accrual occurs during the course of acquisition from less than 200 g of BMC in infancy[8] to more than 2000 g in adulthood.[10]. We previously compared cross sectionally the BMC of a group of black and white boys and girls[10] who subsequently were followed with annual BMC and Tanner stage measurements for up to 4 years. These data allow us to delineate the effects of chronologic age and Tanner stage on the pattern of bone growth velocities in black and white children, even though the age of transition between Tanner stages differs systematically between the races
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