Older women who take calcium supplements to maintain healthy bones could be increasing their risk of heart attacks, according to new research.
The new study, published on bmj.com (British Medical Journal), adds to mounting evidence that calcium supplements increase the risk of cardiovascular events, particularly heart attacks, in older women.
These are often prescribed to post-menopausal women to maintain bone health but the authors of the research suggest their use in managing osteoporosis should now be reassessed.
The new research, led by Ian Reid professor at the University of Auckland, New Zealand, follows the Women’s Health Initiative study – a seven-year trial of more than 36,000 women which found no cardiovascular effect of taking combined calcium and vitamin D supplements.
But the majority of participants in that study were already taking personal calcium supplements, which may have obscured any adverse effects.
Prof Reid’s study looked at data from 16,718 women who were not taking personal calcium supplements at the start of the trial.
It found that those allocated to combined calcium and vitamin D supplements were at an increased risk of cardiovascular events, especially heart attack.
But women who were taking personal calcium supplements at the start of the trial, combined calcium and vitamin D supplements did not alter their cardiovascular risk.
The authors said they suspect abrupt changes in blood calcium levels after taking a supplement causes the adverse effect, rather than it being related to the total amount of calcium consumed.
High blood calcium levels are linked to hardening of the arteries, which may also help to explain these results.
The team conducted further analyses, adding data from 13 other trials, involving 29,000 people altogether.
These also found consistent increases in the risk of heart attack and stroke associated with taking calcium supplements, with or without vitamin D.
In their conclusion, the authors said: “When these results are taken together with the results of other clinical trials of calcium supplements, with or without vitamin D, they strongly suggest that calcium supplements modestly increase the risk of cardiovascular events, particularly myocardial infarction (heart attack).
“These data justify a reassessment of the use of calcium supplements in older people.”
But, in an accompanying editorial on bmj.com, two osteoporosis experts, Bo Abrahamsen, of Gentofte Hospital, Copenhagen and Opinder Sahota, of the Queen’s Medical Centre, Nottingham, argue that there is insufficient evidence available to support or refute the association.
The two professors say study limitations mean 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,” they say.
Cathy 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.