Effects of sex, race, and puberty on cortical bone and the functional muscle bone unit in children, adolescents, and young adults.

CONTEXT

Sex and race differences in bone development are associated with differences in growth, maturation, and body composition.

OBJECTIVE

The aim of the study was to determine the independent effects of sex, race, and puberty on cortical bone development and muscle-bone relations in children and young adults.

DESIGN AND PARTICIPANTS

We conducted a cross-sectional study of 665 healthy participants (310 male, 306 black) ages 5-35 yr.

OUTCOMES

Tibia peripheral quantitative computed tomography measures were made of cortical bone mineral content (BMC) and bone mineral density (BMD), periosteal (Peri) and endosteal circumferences, section modulus (Zp), and muscle area. Regression models were adjusted for tibia length, age, race, sex, and Tanner stage.

RESULTS

All cortical measures were greater in blacks than whites (all P < or = 0.001) in Tanner stages 1-4; however, differences in BMC, Peri, and Zp were negligible in Tanner stage 5 (all interactions, P < 0.01). Cortical BMC, Peri, and Zp were lower in females than males in all Tanner stages (all P < 0.001), and the sex differences in Peri and Zp were greater in Tanner stage 5 (interaction, P < 0.02). Cortical BMD was greater (P < 0.0001) and endosteal circumference was lower (P < 0.01) in Tanner 3-5 females, compared with males. Adjustment for muscle area attenuated but did not eliminate sex and race differences in cortical dimensions. Associations between muscle and bone outcomes did not differ according to sex or race.

CONCLUSION

Sex and race were associated with maturation-specific differences in cortical BMD and dimensions that were not fully explained by differences in bone length or muscle. No race or sex differences in the functional muscle bone unit were identified.