Millions of post-menopausal women take daily calcium and vitamin D supplements with the goal of preventing bone fractures. However, if newly published research is to be believed, taking calcium supplements can do more harm than good when it comes to increasing a woman’s chances for cardiovascular events like heart attacks and strokes.
 
The study, published last month in BMJ, revisited the data generated by the landmark Women’s Health Initiative Study—the study most widely credited with popularizing the benefits of calcium plus vitamin D supplementation. In this most recent study, researchers at the University of Auckland in New Zealand looked specifically at data related to cardiovascular risk and found calcium supplements taken alone or in combination with vitamin D “modestly increase the risk of cardiovascular events, especially myocardial infarction,” a finding the researchers said was “obscured in the WHI CaD Study.”
 
Further, the researcher warned that “A reassessment of the role of calcium supplements in osteoporosis management is warranted,” and that the “potentially detrimental effect should be balanced against the likely benefits of calcium on bone.”
 
Professor Ian Reid, MD, the study’s lead researcher, said this study is a follow up to a related study he and his colleagues previously published that examined the effect of calcium supplements alone and also showed a “significant increase” in heart attack risk.“This left open the question as to whether adding vitamin D to calcium would lessen this adverse effect,” he said. “Unfortunately, vitamin D does not change the outcome, so we conclude that the use of calcium supplements, with or without vitamin D, causes a small but significant increase in risk of heart attacks.”
 
Despite calcium holding a revered place in the public’s spectrum of trust, Dr. Reid said his study results were not surprising. “Several years ago we and others were hypothesizing that calcium might have a beneficial effect on heart disease, because it improves cholesterol levels and blood pressure,” he recalled. “However, a large clinical trial carried out by us in New Zealand to test this hypothesis showed an adverse effect, and the other studies we have published since that time have progressively strengthened the evidence that calcium has an adverse effect on heart health.”
 
As expected, the outcome of this study has not been well-received by the supplement industry.
 
“The methodology of this reanalysis of data raises more questions than it provides answers,” commented John Hathcock, PhD, senior vice president of scientific and international affairs for the Council for Responsible Nutrition (CRN), Washington, D.C. “I wouldn’t put a lot of weight on their conclusions, as it’s more likely those results were a statistical methodology effect, rather than a true health effect.”
 
Dr. Hathcock was also perplexed by the unexpected findings. “For the women not taking personal calcium supplements at the start of the trial, those allocated to combined calcium and vitamin D supplements were at an increased risk of cardiovascular events,” he said. “Conversely, the authors also wrote that for women who were taking personal calcium supplements at the start of the trial, combined calcium and vitamin D supplements did not alter cardiovascular risk.  So in this case, it appears the more you take, the better off you may be. 
 
“Instead of considering these findings a coincidence or a statistical abnormality as there are with many analyses of large pools of data with many variables, the authors instead suggest that the abrupt change in blood calcium levels after supplementation is what causes the effect. It seems more likely that findings are a procedural or statistical anomaly.”
 
Dr. Hathcock also found another facet of the New Zealand study to be interesting. “The authors elected to discuss in the text of the reanalysis those outcomes which would be most contrary to use of supplemental calcium, but barely identified possible beneficial effects,” he said. “For example, while the authors did include data for those who before the trial had ‘any personal use of calcium’ having a highly significant 16% decrease from death from all causes, they chose to ignore that point in their text, having identified it only in a table.”
 
Dr. Reid stands by his results and took the opportunity to make it clear that data referred to calcium supplements, not dietary calcium, stating that there has been no evidence proving calcium-rich foods to have an adverse cardiovascular effect. “We should back off from the use of calcium supplements, encourage people to have adequate calcium in the diet, and provide appropriate medications to those individuals whose risk of fracture is high enough to justify it,” he said.
 
In conclusion, Dr. Reid said the ripple effect of his study could be far-reaching, as it relates to patients ascribing to a daily regimen of calcium supplementation. “Individuals at high risk of fracture should not be relying on calcium alone as their strategy to prevent future fractures,” he said. “The implications of this work are that the use of calcium supplements for the prevention and treatment of osteoporosis probably causes more harm (in terms of heart attacks and strokes) than good (in terms of fractures prevented).”