The influence of calcium intake and physical activity on bone mineral content and bone size in healthy children and adolescents

Studies of determinants of bone mineralization during growth are relevant t o the attempt to increase peak bone mass. The aim of this study was to exam ine how calcium intake and physical activity influence bone size (bone area , BA), accretion in BA, whole body bone mineral content (BMC) and accretion in BMC. BA and BMC were examined by dual-energy X-ray absorptiometry (Holo gic 1000/W) in healthy girls (n = 192) and boys (n = 140) aged 5-19 years a t baseline and 1 year later. Calcium intake was assessed three times by a f ood frequency questionnaire and physical activity three times by a 24 h rec all questionnaire. The influence of calcium intake and physical activity wa s examined by multiple regression. BA was size-adjusted by including height and weight in all analyses, and BMC was size-adjusted by including BA, hei ght and weight in all analyses. Size-adjusted average BA was associated nei ther with average calcium intake nor with average physical activity. Size-a djusted accretion in BA was borderline associated with the average calcium intake in boys only (p = 0.07). Size-adjusted average BMC was positively as sociated with average calcium intake (p = 0.03 girls; p = 0.07 boys) and bo rderline associated with average physical activity level in boys (p = 0.07) but not girls (p = 0.7). Size-adjusted accretion in BMC was significantly associated neither with average calcium intake nor with average physical ac tivity level, but was associated with change in calcium intake over the 1 y ear observation period in boys (p = 0.03) but not girls (p = 0.9). In concl usion, we found that size-adjusted BMC in school-aged children was positive ly associated with average calcium intake. Size-adjusted accretion in BMC w as positively associated with change in dietary calcium intake fn boys only . To what degree this is caused by a reduction in remodeling space is unkno wn.