Bone density and dietary calcium in New Zealand vegans : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Albany, New Zealand

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The restrictive aspect of a vegan dietary pattern warrants attention, as it may lead to individuals unknowingly obtaining low intakes of calcium. Moreover, several international studies have reported low calcium intakes in vegans. Furthermore, prolonged low calcium intakes can result in reduced bone mineral density (BMD) and increased risk of developing osteoporosis later in life. In older adults, a calcium deficiency will exacerbate bone loss as ageing is associated with a decline in BMD. Moreover, pregnant women are at increased risk of developing a calcium deficiency due to the increased demands of calcium that is required for the growth of foetal bone. The evidence of a vegan diet impacting BMD have been inconclusive in the literature, therefore further research is required to understand bone health of vegans. Especially, in the context of NZ vegan adults as the measurement of bone parameters and calcium intakes have not been investigated in this population. Objectives: To describe calcium intake and bone health of NZ adults following a vegan diet. Methods: This cross-sectional study included adults (N=212) (>18yrs), who followed a vegan diet for more than 2 years. Demographic and lifestyle information was obtained from questionnaires. A 4-day food record was completed for analysis of calcium, zinc, protein, magnesium, phosphorus and vitamin C intake and compared to the Estimated Average Requirement (EAR). Weight, height and BMI were obtained, BMD was measured at the hip and spine using dual x-ray absorptiometry (DXA) and reported as Z-scores. Participants were categorised based on BMD Z scores stratified as follows: low BMD (for age and sex) <-2.0 and normal BMD >-2.0. Blood samples were taken for PTH, 25(OH)D and plasma calcium concentrations were corrected for albumin. All values are presented as mean and standard deviation. Differences in bone parameters between BMD groups were analysed using multiple T-tests. A linear regression analysis examined the association between calcium intake, corrected calcium concentrations, serum PTH levels, BMI, and physical activity levels and BMD Z scores at the lumbar spine and femoral neck. Results: Overall, Z scores at the lumbar spine and femoral neck were -0.29 ± 1.12 and -0.24 ± 0.89), respectively. Corrected calcium concentrations were 2.21 ± 0.33 mmol/L. Overall, calcium intake was 917 ± 347.23 (range 195 to 2,429 mg/day). The main source of calcium in the vegan diet was tofu and plant-based milks. The intake of protein (77 ± 27.80) g/day, magnesium (569 ± 181.05) mg/day, and vitamin C (145 ± 96.94) mg/day met the EAR, excluding vitamin and mineral supplements. However, the intake of phosphorus (1,472 ± 459.98) mg/day and zinc (10.6 ± 4.01) mg/day were below the EAR. Only BMI significantly predicted BMD Z-scores at the lumber spine (P = 0.004) and femoral neck (P = 0.003). Conclusion: The study found that most vegans had normal BMD for their age and sex, adequate calcium intakes and bone homeostasis markers. Despite mean intake of calcium exceeding the EAR, very low intakes demonstrated significant variations between participants. Tofu was identified as the main plant-based source of calcium amongst participants. Moreover, longitudinal research is required to understand the long-term impact of a vegan diet on bone health.
vegan diet, calcium, bone, adults