SummaryThe Japanese school lunch program with milk was designed to supply 33-50% of the necessary nutrients per day and 50% of the recommended dietary allowance for calcium, which is difficult to obtain from Japanese meals. Although this program contributes to the mental and physical development of children, the effect of these meals on the bone growth in children remains unknown. Therefore, we compared the effect of school lunch with milk on bone growth between elementary school children attending schools that did not enforce the school lunch with milk program (box-lunch group) and those attending schools that did enforce the program (school-lunch group). The study subjects included fourth-grade children during the 2009-2013 school years, of whom 329 children were in the school-lunch group and 484 children in the box-lunch group. The bone area ratio of the right calcaneus was evaluated using quantitative ultrasound (Benus III). Dietary intakes were assessed using brief self-administered diet history questionnaires. The subjects were asked to record their activities for 3 d so that the mean physical activity intensity and the time spent sleeping could be estimated. The bone area ratios (%) were significantly higher in the school-lunch group than in the box-lunch group (males 31.060.3 vs. 30.360.2; females 30.660.2 vs. 29.760.2). This tendency did not change even after adjustment for confounding factors associated with bone growth. The results suggest that nutrients supplied by the Japanese school lunch program contributed to increased bone growth in elementary school children.

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SummaryThere is little evidence regarding the associations between bone growth and environmental factors among growing children, especially in Asians. The aim of this crosssectional study was to search for the promotion factors of bone growth in Japanese children during growth. The study subjects were male (nϭ333) and pre/post-menarcheal female (nϭ179/nϭ68) school children aged 8-14 y. Bone status at the calcaneus was evaluated by quantitative ultrasound (Benus III), and the bone area ratio (BAR) was used as an evaluation index. Dietary intakes were assessed via brief self-administered diet history questionnaires. The participants were asked to record all of their activities for 3 d (2 weekdays and 1 holiday). They were also required to provide the most recent anthropometric measurement records at their schools and answer questions about the frequency of fractures and, for females, the length of time since menarche. Multiple regression analysis with dummy variables demonstrated that age, magnesium (more than the RDA), vitamin B1 (more than the RDA), mean physical activity intensity per day (more than 1.7 METs), vitamin C (more than the RDA) and calcium (more than the RDA) were signifi cantly positive infl uential factors of BAR for males. For premenarcheal females, age, vitamin A (more than the RDA), BMI, and mean physical activity intensity per day (more than 1.7 METs) were signifi cantly positive infl uential factors of BAR, and for postmenarcheal females, only BMI and age were signifi cantly positive infl uential factors of BAR. The results suggest that several manageable factors correlate with the bone mass, and the associations differ depending on gender and menarcheal status.