Effects of Calcium on Indices of Bone and Cardiovascular Health, and on Cancer

Abstract

Background Calcium supplements are used to promote bone health; however, recent evidence suggests they might also increase cardiovascular risk and reduce cancer risk. The relationship between dietary calcium intake and bone health is unclear. This thesis explores the effects of calcium supplements on serum calcium and how these relate to bone and cardiovascular health; relationships between dietary calcium intake and bone health; and relationships between calcium supplementation and cancer risk. Methods Four studies were performed. 1. A randomised controlled trial on the acute and 3-month effects of different calcium supplements on serum calcium, bone turnover and indices of cardiovascular disease. 2. A cross-over trial on the acute effects on serum calcium of a calcium supplement with a meal, or calcium from fortified juice or dairy products. 3. An analysis of the relationship between dietary calcium intake and bone mineral density (BMD), change in BMD and fracture risk in postmenopausal women, and whether the effect of calcium supplementation is modified by dietary calcium intake. 4. A meta-analysis of randomised controlled trials on the effect of calcium supplementation on the risk of total, colorectal, breast and prostate cancer. Results 1. Serum calcium was acutely elevated following a calcium supplement and this was not diminished with continuous use. A supplement which elevated serum calcium less still suppressed bone turnover comparably. Blood pressure and blood coagulability were increased after a calcium supplement compared with a control. 2. A calcium supplement with or without a meal and calcium from fortified juice elevated serum calcium comparably. Calcium from dairy products elevated serum calcium less. 3. Dietary calcium intake was weakly associated with BMD, but not with change in BMD or fracture risk. The effect of calcium supplementation on change in BMD was not modified by dietary calcium intake. 4. Calcium supplementation was not associated with the risk of total cancer. Conclusions The acute effects of calcium supplements on serum calcium and indices of cardiovascular disease may explain the increased cardiovascular risk associated with calcium supplementation. Dietary calcium intake was not associated with bone health in postmenopausal women, and calcium supplementation was not associated with short-term cancer risk.