Bone Mass of Asian Adolescents in China: Influence of Physical Activity and Smoking

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Abstract
Research addressing the role of biology and behavior on bone development during times of peak bone acquisition in adolescence is limited. The present investigation was conducted to address the influence of body composition (lean body mass, fat mass), menarche, leisure physical activity, sports team participation, smoking, and second-hand smoke on skeletal mass of a unique sample of Asian adolescents in China.A total of 166 girls and 300 boys (ages 12-16 yr) participated in this study. Bone mineral density (BMD) and content (bone mineral content (BMC)) of the forearm and the os calcis were measured using dual energy x-ray absorptiometry (DXA); lean body mass (LBM) and fat mass were estimated by bioelectrical impedance analysis (BIA); grip strength was measured by isometric dynamometry. Menarche, leisure physical activity, sports team participation, and active and passive smoking were determined using questionnaire.In girls, a total of 44% of the variance in forearm BMC was attributed to a model which included LBM (32%), time since menarche (10%), and age (2%); heel BMC was best predicted by LBM alone (42%), with no significant contribution by other variables. In boys, a total of 39% of the variance in forearm BMC was attributed to a model which included LBM (28%), age (5%), sports team participation (4%), height (1%), and fat mass (1%); heel BMC was best predicted by LBM (50%) and height (3%), accounting for 53% of the variance.The findings of this study suggest that lean body mass is the primary determinant of bone mass in Chinese adolescents. Menarche is also an important contributor in girls, whereas age and sports team participation are secondary predictors of bone mass in boys.