The effect of dairy intake on bone mass and body composition in early pubertal girls and boys: a randomized controlled trial

Background: Calcium retention increases with increasing body mass index (BMI) on recommended calcium intakes. Dairy foods are an excellent source of essential nutrients that are needed to increase bone mineral content (BMC) and potentially decrease fracture. Objective: We compared children who were overweight with children who were healthy weight for the accrual of bone mass in response to an extra 3 servings dairy/d compared with usual intake. Design: Participants were 240 healthy boys and girls (64%), aged 8–15.9 y (mean ± SD age: 11.8 ± 1.5 y), who consumed low amounts of dairy (<800 mg Ca/d). A total of 181 subjects completed the trial—61% were black, 35% were white, and 4% were other; 50% of subjects were healthy weight [5th through 70th BMI percentiles for age (percentile)], and 50% of subjects were overweight (≥85th percentile). Participants were randomly assigned within BMI categories to receive an 18-mo dairy intervention (3 servings/d equivalent to ∼900 mg Ca/d) or control. Main outcome measures assessed every 6 mo included the total-body bone mineral content and density, cortical and trabecular bone mineral density (BMD), BMC, and bone area at the 4% tibia and anthropometric measures. Results: No significant differences in the change of BMD, BMC, or bone area for the total-body radius, lumbar spine, and total hip were observed between subjects who received the dairy intervention (achieved consumption of 1500 mg Ca/d) and subjects who did not (achieved 1000 mg Ca/d, which represented ∼2 cups milk or other dairy as part of the diet) with the exception of a tibial BMC gain, which was greater in the group who were given dairy (P = 0.02). Body fat was not influenced by the diet assignment. Conclusions: Dairy food interventions generally had no effect on bone mineral acquisition or body composition either within or between weight groups. This study suggests that 2 cups milk or the dairy equivalent is adequate for normal bone gain between ages 8 and 16 y. This trial was registered at clinicaltrials.gov as NCT00635583.