The new data, published in the British Medical Journal, suggests that calcium supplements – when taken with, or without vitamin D – may increase the risk of heart attack by 25 per cent, and the risk of stroke by 15 per cent. The new findings back up the results of an earlier meta-analysis that suggested calcium supplementation could have more risks than benefits.
Professor Ian Reid, senior author of the study, told NutraIngredients that the new data provides “a significant body of evidence that says there is a concern.”
“When we do the calculations from these 29,000 people, we find that for every thousand people we give calcium to for five years, we cause six heart attacks and we prevent three fractures,” said Reid.
“The message from last years study, to this years study is very consistent, and that is that it’s not a very effective way of preventing fractures, and it probably does carry a significant risk,” he warned.
Last year, Professor Reid and his researcher team published a study suggesting that regularly supplementation with calcium to reduce the risk of osteoporosis may cause more heart attacks than the number of fractures they prevent.
The previous study (reported here) looked at calcium supplementation alone, however many people take calcium combined with vitamin D, so Reid and his team then set out to see if their findings held true when this was taken into account.
Prof. Reid said that the new research was “not so much a re-analysis”, but a new study, which includes a re-analysis.
“What we have done is now found three studies which have calcium plus vitamin D as the intervention … that’s another 17,000 new people in which we looked at the incidence of heart attacks and strokes,” he explained
The results of studying these 17,000 people showed “exactly the same increase in risk from this as we found before” said Reid. “So then we went ahead and combined this data with the data from last year’s meta-analysis of 12,000 people to give us a total meta-analysis of 29,000 people,”
From this overall data, the researchers found a 25 per cent increase in the risk of heart attack, and a 15 per cent increase in the risk of stroke.
“Those effects are much the same as we found last year in terms of the risk size, but now because we have a much larger pool of people, the differences in the data have much higher statistical significance,” said Reid.
“We have a very consistent pattern … you find that in the major studies heart attack risk is very consistent, irrespective of whether or not they are taking vitamin D with the calcium,” concluded Reid.
The research team are now investigating the mechanisms behind the effects of calcium supplementation to try and understand why taking supplements may pose a risk to heart health, whilst consuming calcium rich food does not.
Reid told NutraIngredients that finding the mechanisms behind the potential increased risk opens up the possibility of designing calcium supplements that are safer to use.
He confirmed that they are currently working with industry, “to look at ways or means of creating a safer way to deliver calcium to people,” adding that research team is happy to work more with industry “to look into these issues and try to come up with solutions.”
Prof. Reid warned that supplement manufacturers must pay attention to the risks as well as the benefits of calcium supplementation, adding that ignoring or dismissing the issue is not a suitable answer.
“The forms of supplements we are using at the minute are measurably not safe, and I think that if industry ignores that fact, or refuses to engage, it may be opening itself up to liability in the future,” he warned.
Industry groups have been quick to react to the study; John Hathcock, senior vice president of scientific and international affairs at the Council for Responsible Nutrition (CRN) told NutraIngredients that he “wouldn’t put a lot of weight” on the conclusions, adding that he believed the methodology of the study “raises more questions than it provides answers.”
“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,” said Hathcock.
Reid responded by adding that he knew the research findings would be “a high stake statement.” He said the “net losers would of course be industry […] because it has substantial impact on all the people who take calcium and also on all the people who make it.”
“For that reason we have been expecting very close scrutiny and I think we have been particularly meticulous in the way we carried out this analysis so that any scrutiny doesn’t hold problems for us,” he said.
Source: British Medical Journal
Published online ahead of print, doi:10.1136/bmj.d204
“Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women’s Health Initiative limited access dataset and meta-analysis”
Authors: M.J. Bolland, A. Grey, A. Avenell, G.D. Gamble, I.R. Reid