Calcium supplements: bad for the heart?
- Department of Medicine, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
- Correspondence to Professor Ian R Reid, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand;
Contributors IRR wrote the first draft of this manuscript, after discussions between the two authors, which was then critically reviewed and amended by MB.
Calcium is a micronutrient widely believed to affect bone heath, though the importance of normal variations in calcium intake may have been overemphasised.1 2 Because its principal dietary source is dairy products, and because high dairy intakes are not acceptable to many older people, there has been a strong move in recent decades to increase the intake of calcium by supplements. This is most prevalent for the prevention of postmenopausal osteoporosis, but is also used in the management of serum phosphate levels in patients with renal failure. However, the safety of calcium supplements is now coming under considerable scrutiny. Their use in osteoporosis had caused concern with respect to the risk of renal calculi, which is increased by about 20%.3 There has also been a longstanding awareness that they cause gastrointestinal symptoms, particularly constipation, but it is more alarming to find that they double the risk of admission to hospital with an acute abdominal condition.4 The concern that most threatens their continuing use, however, is their potential risk to cardiovascular health. Although there is trial evidence that calcium supplements can improve high-density lipoprotein/low-density lipoprotein ratios by almost 20%, and reduce both systolic and diastolic blood pressure by a few mm Hg, this does not appear to translate into fewer cardiovascular events. This concern first surfaced in nephrology practice with evidence that calcium supplements exacerbated vascular calcification and contributed to the very high cardiovascular mortality experienced by those patients. Randomised trials in pre-dialysis patients have demonstrated acceleration of coronary artery calcification,5 and some trials have shown increased cardiovascular mortality in patients randomised to calcium.6
More recently, the focus of concern about cardiovascular …