Associations between physical activity, body composition, nutrient intake, and bone mineral density in pre-menopausal Pacific Island women living in New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Albany, New Zealand

Abstract

Background/Aim: Anecdotally it is suggested that Pacific Island women have good bone mineral density (BMD); however little evidence for this or for associated factors exists. The aim of this study is to explore associations between several key predictors of bone health with bone mineral density, as measured by BMD (g/cm2), in pre-menopausal Pacific Island women. Methods: Healthy pre-menopausal Pacific Island women (n=91; age 16-45y) were recruited. Participants’ body composition and total body BMD were assessed using DXA and air-displacement plethysmography (BodPod). A food frequency questionnaire (FFQ) and current bone-specific physical activity questionnaire (cBPAQ) were completed. Variables that significantly correlated with BMD were applied to a hierarchical multiple regression analysis. Results: The mean BMD was 1.1 g/cm2 ± 0.08. Bone-free, fat-free lean mass only (LMO, 52.4kg ± 6.9) and total mass (90.4kg ± 19) were the only factors to show a significant correlation with BMD. Body-fat (38.4% ± 7.6), cBPAQ score (1.7 (0.4,5.2)), and dietary calcium (1016mg ± 442), protein (18% ± 3.8) and vitamin C (125mg (94, 216)) showed no correlation with BMD. The regression analysis suggests that LMO is the most important predictor of BMD, explaining 13.4% of the variance, while total mass accounts for a further 2.5% of the variance. Together, these factors explain a total of 15.9% of the variability. Conclusions: LMO is the strongest predictor of BMD, while many established contributors to bone health (calcium, physical activity, protein, and vitamin C) do not appear to be associated with BMD in this population. As just 15.9% of the variability can be explained, further research is needed in this area. Key words: Bone mineral density, Pacific Island, pre-menopausal, body composition, physical activity, dietary intake