Bone mass in Chinese premenarcheal girls: the roles of body composition, calcium intake and physical activity

The association of growth and anthropometric characteristics and lifestyle factors with bone mass and second metacarpal radiogrammetry parameters was evaluated in 373 healthy Chinese premenarcheal girls aged 9-11 years. Bone mineral content (BMC) and density (BMD) and bone area (BA) of distal forearm, proximal forearm and total body, bone mineral-free lean (BMFL) mass and fat mass were measured by dual-energy X-ray absorptiometry. Metacarpal bone periosteal and medullary diameters were measured. Dietary intakes were assessed by 7 d food record and physical activity (PA) by questionnaire. BMFL and fat mass together explained 6.3 and 51.6 % of the variation in total body BMC and BMD, respectively. BMFL mass contributed to a substantial proportion of the variation in forearm BMC and BMD and periosteal diameter (10.4-41.0 %). The corresponding BA explained 14.8-80.4 % of the variation in BMC. Other minor but significant predictors of total body bone mass were Ca intake, height, age and PA score (BMD only), and of forearm bone mass were PA score, bone age, height and fat mass. Nevertheless, after adjusting for bone and body size and for age or bone age, subjects with Ca intake above the median (417 mg/d) had 1.8 % greater total body BMC (P<0.001), and subjects with PA scores above the median had 2.4-2.5 % greater distal and proximal forearm BMC (P<0.05) than those below. Vitamin D intake negatively associated with medullary diameter (partial R-2 1.7 %). The results indicate that premenarcheal girls should be encouraged to optimise nutrition and Ca intake and exercise regularly to achieve maximum peak bone mass.