Oral Presentation 29th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2019

Obesity is associated with reduced bone turnover and inferior bone microarchitecture, despite often exhibiting higher bone mineral density (BMD), the reasons for which are not fully understood. Indeed, whether obesity alters the effects of recommended calcium supplementation to suppress bone resorption remains unknown. To investigate the acute effects of calcium consumption on lowering bone resorption in women with varying BMI and visceral adipose tissue (VAT) levels, 77 post-menopausal women underwent measures for weight, height, and total BMD and VAT levels by DXA analyses. Each week, fasting participants were randomized to receive a single oral dose of either milk (1000 mg Ca), calcium carbonate tablet (1000 mg Ca), and fruit juice (no calcium control). At each session, blood samples were collected at 0, 0.5, 1, 2, 3, 4, and 5h post-consumption. Serum CTX-1, PTH, were measured at all time points and serum 25D, 1,25D, BSAP, OC were measured at baseline. Serum calcium was measured at baseline 1hr, 2hr, 4hr & 5 hr. Institutional Human Ethical approval was obtained. The mean age of participants was 65.6±4.5, with BMI range of 18.3 - 53.9 kg/m² and VAT range of 91-3392 cm³. VAT correlated inversely with CTX-1 levels (r=-0.36, p=0.002) and positively with whole body BMD (r=0.43 p<0.001). CTX-1 suppression due to milk consumption was maximal 2h post-consumption (P<0.001). While the maximum CTX-1 reduction with calcium carbonate tablet consumption was comparable to the milk consumption group (44%), it occurred later at 4 and 5h post consumption . The highest suppression in CTX (absolute value) was observed in women in lowest tertile of VAT for both milk and tablet. While obese women may exhibit altered response to recommended dietary calcium supplementation, it remains important to emphasize inclusion of recommended levels of calcium through dietary source or as supplement irrespective of BMI or VAT levels.