Factors associated with bone mineral density and content in 7-year-old children

Abstract

Objective To evaluate the bone status of 7-year-old school children in Reykjavik, Iceland, and to see if gender, height, lean body mass and fat mass is associated with bone mineral density (BMD) and bone mineral content (BMC) in the lumbar vertebrae and hip. Study design A cross-sectional study of a sample of 7-year-old school children. Setting Six elementary schools in Reykjavik, Iceland. Subjects All children attending second grade in these six schools were invited to participate. Three hundred twenty-six children were invited and 211 (65%) participated in the study. Main outcome measures Lean body mass, bone mineral density, bone mineral content and total fat mass. Results Both BMD and BMC were positively correlated with sex, height and lean body mass. Fat mass was positively correlated to BMC but not BMD in the total body and lumbar vertebrae. When analyzed with multiple linear regression, the bone area and lean body mass (LBM) were positively associated with BMC in the hip and total body, but total fat mass (TFM) was negatively associated with BMC, the model explaining about 88% of the variance ( R 2) in the total body bone mineral content (TBMC) and 74% of the variance ( R 2) in the BMC of the hip. LBM was positively associated with total body bone mineral density (TBMD) but TFM negatively associated. Neither height nor gender contributed to total BMC and BMD in our multiple linear regression models. Conclusion The study emphasizes that fat mass may play different roles in children and adults and that both LBM and TFM should be taken into consideration when interpreting BMC and BMD for children.