Calcium supplements, which are often prescribed to postmenopausal women, appear to raise the risk of cardiovascular events, especially heart attacks in older females, researchers from the University of Auckland, New Zealand, revealed in the BMJ (British Medical Journal). Older women take calcium supplements to maintain good bone health - the authors suggest that doctors should consider reassessing their use.
Postmenopausal women are sometimes prescribed vitamin D combined with calcium supplements. The authors explain that nobody has yet known whether the impact on the heart is just with calcium supplements, or together with vitamin D.
According to data from a 7-year trial involving more than 36,000 women (Women's Health Initiative, or WHI), no evidence of cardiovascular effects were linked to taking combined calcium and vitamin D supplements. However, most of the females had already been taking personal calcium supplements, which may have compromised the findings.
Professor Ian Reid and team re-examined the WHI data to see whether they could predict cardiovascular event risk according to calcium supplement intake, with or without vitamin D.
They gathered data on 16,718 women who had not been taking personal calcium supplements when the trial began. They found that those prescribed combination calcium and vitamin D supplements had a higher risk of having a cardiovascular event, especially a heart attack.
However, they found no association between combined calcium and vitamin D supplements and cardiovascular event risk among the women who had been taking personal calcium supplements when the trial began.
The researchers believe that the sudden change in blood calcium levels, which occurs when patients start taking the supplement, causes the adverse effects, and not the amount of calcium being consumed. People with high blood calcium levels tend to have a higher risk of hardening (calcification) of the arteries.
The researchers looked into 13 more trials involving 29,000 women and found a link between stroke and heart attack risk and taking calcium supplements, with or without vitamin D.
Accompanying EditorialProfessors Bo Abrahamsen and Opinder Sahota say that, according to available evidence, it is not yet possible to confirm or deny a link between calcium supplements and cardiovascular event risk.
Due to the limitations of the study, they write:
"It is not possible to provide reassurance that calcium supplements given with vitamin D do not cause adverse cardiovascular events or to link them with certainty to increased cardiovascular risk. Clearly further studies are needed and the debate remains ongoing."
British Heart Association ResponseCathy Ross, Senior Cardiac Nurse at the British Heart Foundation, said:
"The study showed there was a modest increase in heart attack or stroke risk but that's not the same as saying calcium supplements with vitamin D cause heart attacks and strokes, only that there was an increased risk.
"It's very important further studies are carried out to determine the effects of calcium supplements on heart health. We also need to know whether any increased risk outweighs the benefits these supplements have in treating the debilitating effects of conditions such as osteoporosis.
"There is still not enough evidence to confirm the association between calcium supplements and cardiovascular risk so patients prescribed the supplements shouldn't stop taking them, but should discuss any concerns they have with their doctor."
"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"
Mark J Bolland, Andrew Grey, Alison Avenell, Greg D Gamble, Ian R Reid
BMJ 2011; 342:d2040 doi: 10.1136/bmj.d2040
Written by Christian Nordqvist