The relationship between dairy intake, body composition, physical activity, and bone health among pre-pubertal children : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Human Nutrition at Massey University, Palmerston North, New Zealand

Abstract

Objective: To examine the effects of dairy intake, body composition parameters, and physical activity on the bone mineral status of pre-pubertal children. Study design: This was a cross-sectional study of 45 healthy pre-pubertal children aged 5-10 years. Total headless bone mineral content (tBMC), total headless bone mineral density (tBMD), lumbar spine bone mineral content (LS-BMC), and lumbar spine bone mineral density (LS-BMD) were measured with dual energy x-ray absorptiometry (DEXA). Dietary calcium intake was assessed using a food frequency questionnaire (FFQ) and a 3-day estimated food record. Anthropometric data was collected and a previous day physical activity recall (PDPAR) was used to measure the physical activity as metabolic equivalents of task (METs) and energy expenditure (EE). The FFQ was also validated against the 3-day estimated food record. Results: The average daily serves of dairy consumed by children were above the recommended levels. Similarly the FFQ analysis also showed mean calcium intake of the sample to be higher than the recommended dietary intake (RDI) level. Boys had significantly higher lean body mass (LBM) than girls (p <0.02). Girls on the other hand had significantly higher percent body fat (%BF) compared to boys (p<0.0005). Multiple linear regression analyses for the population sample showed no significant association was present between calcium or dairy intake and any bone parameters. Furthermore, calcium/dairy intake was also not significantly related to body composition, physical activity, and anthropometric variables. tBMC and tBMD did show a positive significant relationship with LBM and TFM but an inverse significant association with %BF. Average EE showed a significantly positive relationship with tBMD only. Whereas, METs were a negative significant predictor of only %BF. Validation of the FFQ showed that it overestimated daily calcium intake. Conclusions: Calcium or dairy intakes were not significantly associated with bone health status. LBM, TFM, and %BF are important significant predictors of children’s bone health. And finally, physical activity has beneficial effects upon the bone health and body fat.