[The association between body fat distribution and calcaneal bone mineral density in children and adolescents aged 6-16 years in Beijing].

Objective: To understand the association between body fat distribution and calcaneal bone mineral density (BMD) in children and adolescents aged 6-16 years in Beijing. Methods: Children and adolescents were selected in 30 schools (8 primary schools, 21 middle schools and one 12-year education school) from Dongcheng, Tongzhou, Fangshan and Miyun districts of Beijing by using a stratified cluster sampling method from November 2017 to January 2018. A total of 15 030 students in grade 1 to 4 of primary school, grade 1 of junior and senior middle school were enrolled after excluding subjects who were not able to participate into this study due to trauma or other uncomfortable physical conditions or with missing key values or with diabetes and kidney diseases. Questionnaire survey, body composition and calcaneus bone mineral density were conducted. The relation of fat mass percentage (FMP), trunk to total fat ratio (TrTFR), trunk to limb fat ratio (TrLFR), limb to total fat ratio (LTFR) and viscera to total fat ratio (VTFR) with calcaneus BMD were assessed using the multivariate linear regression models after adjusting for possible confounding effects. The central fat distribution types were divided into 4 groups including type 1: both trunk fat and visceral fat greater than the sex-and age-specific internal P (75); type 2: barely trunk fat greater than P (75); type 3: barely visceral fat greater than P (75); type 4: both trunk fat and visceral fat greater than P (75). The central fat distribution types were included into the model in the form of dummy variables to analyze its relationship with calcaneal BMD. The sex-and age-specific z-scores of fat distribution indicators and BMD were calculated. Results: A total of 15 030 participants aged (11.4±3.3) years (50.2% boys) were involved in the analysis. In both genders, after adjusting for age, height, lean mass index, smoking, drinking, physical activity, milk intake, vitamin D and calcium supplementation, FMP, TrTFR, TrLFR and VTFR were negatively correlated with calcaneal BMD (all P value<0.05), while LTFR was positively associated with calcaneal BMD (all P values<0.05). Compared to the central fat distribution type 1, the regression coefficients (95% CI ) of type 2, 3 and 4 were -0.253 (-0.418, -0.087), -0.385 (-0.567, -0.204) and -0.428 (-0.487, -0.369) in boys, respectively; the regression coefficients (95% CI ) of type 3 and 4 were -0.158 (-0.301, -0.015) and -0.226 (-0.290, -0.163), respectively. Conclusion: Body fat distribution and central fat distribution in children and adolescents were correlated with calcaneus bone mineral density.