Medical research suggests that people taking calcium supplements have a higher risk of heart attack.
The study, published in the British Medical Journal, found that calcium from dietary sources did not increase the risk.
Calcium supplements are often taken by older people for the prevention and treatment of osteoporosis.
Researchers have been analysing the results of 11 different studies carried out on some 12,000 people.
Those taking supplements equating to 500mg of calcium per day were compared to those not on supplements.
People taking the supplements were found to have about a 30% higher risk of heart attack.
It is understood the supplements increase the levels of calcium circulating in the blood.
Experts believe higher blood serum levels lead to hardening of the arteries, which can cause heart attacks.
The study said diets high in calcium from natural sources do not increase the risk of heart attack.
It recommends that doctors review their use of calcium supplements for managing osteoporosis in older people.
Meanwhile, Professor Moira O'Brien, President of the Irish Osteoporosis Society, described the study as misleading, saying it did not look at patients who were taking vitamin D with their calcium supplements.
