The British Medical Journal has published the results of a study that has linked calcium supplementation to an increased risk of cardiovascular events. This study has been widely reported in the media: BBC, The Times. It has also been covered on the NPCi blog and NHS Behind the Headlines article.
The study was a secondary analysis of a randomised placebo controlled trial involving 1,472 post-menopausal women. Patients were given 1,000mg of elemental calcium as citrate salt or matching placebo. Data were collected over five years for cardiovascular outcomes including death, myocardial infarction, angina, other chest pain, stroke and transient ischaemic attack. This was a secondary analysis of a study that was originally designed to assess the effects of calcium on bone density and fracture incidence.
The study found an increased risk of myocardial infarction (45 events versus 19 events, P=0.0099, RR 2.24 [95% CI 1.20 to 4.17]) and an increased risk in a composite end point of myocardial infarction, stroke, or sudden death (101 events versus 54 events, P=0.0075, RR 1.66 [95% CI 1.15 to 2.40]).
The study is open to some criticism however:
- Calcium supplementation did not include Vitamin D which is routine practice in the UK
- More patients in the calcium arm smoked at baseline (3.4% versus 2.6%)
- More patients in the calcium arm were former smokers at baseline (40.3% versus 37.2%)
- Events were self reported by patients, when these were verified a smaller number of events were confirmed
- It is a reasonably small population to follow up for 5 years
- It is a secondary analysis of a trial originally designed and powered to answer another question
The NPCi blog concludes that the decision to prescribe a calcium and vitamin D supplement should "take into account the patient's risk of CV disease and osteoporosis. Calcium supplementation alone should not generally be prescribed to postmenopausal women for fracture prevention".
Action: Clinicians should be aware of this study and the media coverage. The information and articles above will provide sufficient information to allow clinicians to discuss this topic with worried patients.
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