Calcium supplements in osteoporosis

Following the publication of an article by Mark Bolland and co-workers in the British Medical Journal of 29 July 2010, on the association between calcium supplementation and risk of myocardial infarction, much concern and confusion exists among patients and doctors alike as to the safety and efficacy of these agents. NOFSA would like to make the following statement and recommendations.

(i) What was known about calcium supplementation prior to the Bolland article

  • Treatment of osteoporosis with calcium supplements alone has only a modest effect on fracture prevention. Calcium has however been a mandatory component of every drug trial using potent anti-fracture medicines (e.g. the bisphosphonates or strontium ranelate) and is thought to have an additive effect when used in combination with these drugs. These studies employing antifracture drugs plus calcium have generally been associated with a significant reduction in all - cause mortality.
  • An adequate calcium intake is thought to be associated with a reduction in high blood pressure and cholesterol. To date, calcium supplementation was thought to be safe. In patients with kidney failure, calcium supplements may however increase calcification of the arteries.
  • The large Women’s Health Initiative (27,000 subjects) clearly showed that calcium, taken with a low dose Vitamin D, was associated with a reduction in cardiovascular risk compared with subjects taking a placebo.

(ii) The article

  • The Bolland article, which emanates from a reputable research group in New Zealand and was published in a distinguished journal, is not an original prospective study but a meta-analysis of 11 previously published randomised controlled trials (RCTs) involving some 12,000 subjects. It reports a modest (27%) but significant increase in myocardial infarction in patients taking calcium supplements for osteoporosis. None of the individual RCTs from which this study was compiled, reported any significant cardiovascular effects.
  • No significant increase in mortality or incidence of stroke was reported in the current study
  • The current study selected RCTs with an exceptionally high dose of supplemental calcium, the average dose being 1,200 mg/day, and a number of studies used doses of 1,500 – 2,000 mg/day. Furthermore, the dietary calcium intake in these subjects was above average (900mg/day) and a positive correlation was found between the proposed increase in cardiovascular disease (CVD) and the dietary intake of calcium. In fact, the increase in CVD was entirely limited to those with a calcium intake of more than 800 mg/day.

(iii) NOFSA recommends:

  • An adequate calcium intake is important for normal bone health. This should preferably be accomplished by consuming sufficient dairy (low fat) products in the diet.
  • Calcium supplementation, in a dose of 500 mg /day is acceptable and safe
  • When such calcium supplementation is given in combination with  vitamin D and /or one of the potent bone active drugs for the management of osteoporosis, the calcium should be continued since there is no evidence that it increases the risk of CVD.
  • High dose calcium supplementation in patients already consuming ample dairy, and especially those with known kidney failure or CVD, is unnecessary and should be avoided.

(Prof Stephen Hough, NOFSA, August 2010)

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