Effect of calcium and vitamin D fortified milk on bone markers and vitamin D status of active, premenopausal women in Palmerston North, New Zealand : 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 evaluate the effects of 12 weeks supplementation with calcium and vitamin D fortified milk on vitamin D status and bone turnover markers; osteocalcin and C-telopeptide of type 1 collagen, of active, healthy premenopausal women aged 30-45 years old in Palmerston North, New Zealand. Methods: The study was a repeated measure design. Forty three premenopausal women were recruited. Participants received two daily servings (2 x 30 g) of fortified milk (1200 mg/d calcium and 10 μg/d vitamin D) over 12 weeks. Anthropometric characteristics were measured for screening by body mass index and bone density measurement. Dietary information was collected using an estimated 3-day food record and a food frequency questionnaire. Blood samples were taken for a screening blood test and to measure plasma 25(OH)D3, interleukin-6, and bone turnover markers; C telopeptide of type I collagen (CTx) and osteocalcin. Usual physical activity levels were estimated using the SPARC short-form New Zealand Physical Activity Questionnaires in face-to-face interviews and were objectively measured using accelerometers in a self-selected group of 25 women. Results: A significant increase in plasma 25(OH)D3 was found (from 69.75 ± 15.87 nmol/L at baseline to 87.83 ± 19.06 at week 12, mean ± standard deviation; p-value <.0001). There were significant reductions in the levels of CTx (0.31 ± 0.12 to 0.21 ± 0.09 μg/L, p-value <.0001) and osteocalcin (22.63 ± 6.64 to 19.64 ± 6.25 μg/L, p-value 0.0003). Dietary calcium intake was 1013 ± 367 mg/day and vitamin D intake was 3.9 ± 2.1 μg/day. The duration of physical activity in the questionnaire and accelerometer were 115 ± 74 and 415 ± 319 (light physical activity), 208 ± 225 and 289 ± 143 (moderate physical activity) and 126 ± 130 and 59 ± 61 minutes (vigorous physical activity) respectively. Conclusion: Calcium and vitamin D fortified milk supplementation improved vitamin D status and decreased bone turnover markers in active premenopausal women aged 30-45 years old over a period of 12 weeks.