Shorter sleep may be a risk factor for impaired bone mass accrual in childhood.

The purpose of the study was to investigate whether sleep duration during early childhood was associated with fat mass and bone mineral content (BMC). BMC and fat mass were measured by dual-energy X-ray absorptiometry in children (n=336) aged 4-12 yr. Sleep was quantified according to parental report of hours slept at night and napping. The relationship between sleep pattern and body composition was tested using analysis of variance including confounding factors. Based on the sample distribution, children were grouped into tertiles of sleep duration. BMC was greater in children with longer sleep duration (p=0.02). Age was inversely associated with sleep duration; therefore, the sample was analyzed by age category using age 7 yr as a cut-off point. The relationship remained significant only among younger children. Napping was positively associated with BMC (p=0.001). Sleep duration was not associated with fat parameters. Longer sleep duration may allow for optimal energy resource partitioning in which bone is favored. Sleep duration of less than 8h may impair bone mass accrual, particularly during periods of rapid growth.