Volume 189 - Issue 1
Calcium supplementation does not increase mortality
Authors: Mark J Bolland, Andrew B Grey and Ian R Reid
Med J Aust 2008; 189 (1): 55-56. || doi: 10.5694/j.1326-5377.2008.tb01909.x
Published online: 7 July 2008
Published online: 7 July 2008
To the Editor: We believe that Tang and Nordin1 misunderstood the findings of our recent study of calcium supplementation.2
We disagree with their claim that the increase in the number of women with self- or family-reported myocardial infarction, stroke or sudden death became non-significant after adjustment for covariables. They correctly noted that the increased number of women experiencing the composite endpoint of cardiovascular events (after adjudication of events and inclusion of unreported events from hospital records) was not statistically significant. However, the increased event rate for this composite endpoint with calcium was statistically significant (rate ratio, 1.43; 95% CI, 1.01–2.04; P = 0.043). Thus, in our study, the number of women needed to treat with calcium for 5 years to cause one cardiovascular event was 29, and the corresponding number to prevent one fracture was 50.2
Tang and Nordin then meta-analysed data from five studies of calcium and vitamin D supplementation to conclude that calcium supplementation does not increase mortality.1 We disagree.
For one of the studies, they classified a subgroup of participants who received annual vitamin D but no calcium supplements as having received “calcium supplementation”.3 Further, for the RECORD (Randomised Evaluation of Calcium Or vitamin D) study, they compared the number of deaths between people receiving and not receiving vitamin D (16.5% v 17.4%) rather than between those receiving and not receiving calcium (17.7% v 16.2%).4 The trend for increased deaths with calcium supplementation in RECORD was greater when analysis was restricted to those treated with calcium monotherapy (18.5%) and placebo (16.3%).
As our study was of calcium monotherapy, the results of Tang and Nordin’s meta-analysis are of questionable relevance to our findings. In addition, ours was a 5-year study, and the differences in vascular events between the groups only emerged after 2 years.2 Only one study in Tang and Nordin’s meta-analysis had an average follow-up duration of more than 25 months.4
Further, there is evidence from other studies of trends towards vascular events occurring more frequently in people who take calcium monotherapy.2,5,6 In three out of four studies that reported mortality, there were trends towards increased death rates in people receiving calcium.2,4-6 As we concluded,2 these data are not definitive, but flag cardiac health as an area of concern in relation to calcium use.
Finally, we did not suggest that calcium supplementation should not be given to older women. However, in view of the evidence that any fracture risk reduction with calcium is small (< 10%),7,8 and the suggestions that calcium supplementation might increase the risk of hip fractures9-11 and vascular events, it seems reasonable and timely to reassess the role of calcium supplementation.
References
- Tang BMP, Nordin BEC. Calcium supplementation does not increase mortality [letter]. Med J Aust 2008; 188: 547.
- Bolland MJ, Barber PA, Doughty RN, et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ 2008; 336: 262-266. 0_i1091876
- Harwood RH, Sahota O, Gaynor K, et al. A randomised, controlled comparison of different calcium and vitamin D supplementation regimens in elderly women after hip fracture: the Nottingham Neck of Femur (NoNOF) Study. Age Ageing 2004; 33: 45-51. 0_i1091878
- Grant AM, Avenell A, Campbell MK, et al. Oral vitamin D3 and calcium for secondary prevention of low-trauma fractures in elderly people (Randomised Evaluation of Calcium Or vitamin D, RECORD): a randomised placebo-controlled trial. Lancet 2005; 365: 1621-1628. 0_i1091880
- Prince RL, Devine A, Dhaliwal SS, et al. Effects of calcium supplementation on clinical fracture and bone structure: results of a 5-year, double-blind, placebo-controlled trial in elderly women. Arch Intern Med 2006; 166: 869-875. 0_i1091882
- Baron JA, Beach M, Mandel JS, et al; The Calcium Polyp Prevention Study Group. Calcium supplements for the prevention of colorectal adenomas. N Engl J Med 1999; 340: 101-107. 0_i1091884
- Tang BMP, Eslick GD, Nowson C, et al. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. Lancet 2007; 370: 657-666. 0_i1091886
- Freyschuss B, Ljunggren O, Saaf M, et al. Calcium and vitamin D for prevention of osteoporotic fractures. Lancet 2007; 370: 2098-2099; author reply 2099. 0_i1091888
- Bischoff-Ferrari HA, Dawson-Hughes B, Baron JA, et al. Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials. Am J Clin Nutr 2007; 86: 1780-1790. 0_i1091890
- Reid IR, Bolland MJ, Grey A. Effect of calcium supplementation on hip fractures. Osteoporos Int 2008; 20 Feb [Epub ahead of print]. 0_pgfId-1732483
- Cumming RG, Cummings SR, Nevitt MC, et al. Calcium intake and fracture risk: results from the study of osteoporotic fractures. Am J Epidemiol 1997; 145: 926-934. 0_i1091894