Late last year, a new health controversy grabbed the media spotlight: a report questioning the need for a supplement that has been a longstanding nutritional touchstons for women past 40: calcium. Last month, the British Medical Journal suggested that calcium supplements could increase a woman’s risk for heart attack or stroke. We asked Timothy C. Dutta, a member of the WVFC Medical Advisory Board and a cardiologist, to weigh in. Here’s his take on the topic.
Low calcium intake is associated with increased risk of osteoporosis. It has seemed logical that taking calcium supplements would lower the risk of fractures, but supplementing calcium has never been a very good treatment for osteoporosis. Multiple studies designed to show the benefit of calcium supplements for preventing fractures have actually shown mixed results. The benefit at best is small and only for women who are extremely compliant about taking the supplements. In the Women’s Health Initiative Calcium/Vitamin D Supplementation (WHI CaD) trial, for every 1,000 women who took calcium supplements, three fractures were prevented (Bolland MJ, Et al. BMJ 2011;342:d2040). Our widespread recommendations to take calcium have less to do with their efficacy and more to do with the perception that they are relatively harmless.
Starting last year, reanalysis of old trials have begun to question the safety of calcium supplements. When meta-analyses last year showed a possible cardiac risk to calcium supplements, questions that arose included: Does dose matter? Does vitamin D matter? This newest analysis begins to address these questions as well. This latest study, published last month in the British Medical Journal, again ties calcium supplements to increased vascular risk of myocardial infarction (heart attack) and stroke. This paper reanalyzes the WHI CaD trial and better differentiates between women who were and were not taking calcium supplements before the trial. The authors hypothesized that calcium supplements were so routine when this enormous trial was begun that the trial could not cleanly separate women into groups who really were or really were not taking calcium supplements.
The authors were again able to show an increased vascular risk (heart attack and stroke) with calcium supplements. The absolute risk was low, but the relative risk for heart attack or stroke was each increased by about 20 percent. This effect was apparent with even 500 milligrams of calcium a day. Vitamin D taken with the calcium did not seem to alter the risk.
This is another reanalysis of old data that is prone to bias because the trial was not originally designed to look at vascular risk. But I think there are two reasons doctors need to pay attention and reconsider whether to recommend calcium supplements. First, 13 trials individually show this increased risk of heart attack. Second, even though the risk of heart attack appears small, so is the ability of calcium to prevent fractures.
For the type of women enrolled in WHI CaD, the authors state: “Treating 1,000 people with calcium or calcium and vitamin D for five years would cause an additional six myocardial infarctions [heart attacks] or strokes and prevent three fractures.”
I am inclined to believe this data until we have better quality studies to properly answer the question of heart attack and stroke risk from calcium supplements. In the meantime, patients at higher risk of heart attack and stroke should reconsider the risks of calcium supplementation against the benefits.