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Women Taking calcium supplements to cut their risk of fracturing frail and thinning bones are more likely to have heart attacks and strokes, a major new University of Auckland study has found.
The new findings are expected to cause widespread alarm among the estimated 300,000 mainly elderly New Zealand women who suffer from the brittle bone disease, osteoporosis.
Calcium supplements - often prescribed by doctors - have long been associated with better bone health, with many international trials showing a regular intake of calcium helps to cut the risk of broken bones in the elderly by almost a quarter.
A buildup of calcium in blood vessels and heart valves increases a person's risk of heart disease but until now, the relationship between dietary calcium and cardiovascular problems had been uncertain. The study is awaiting publication in a medical journal, but was presented at a conference in the United States a fortnight ago.
In the University of Auckland study, 1500 postmenopausal women were randomly assigned to take a placebo or 1000mg of calcium - the equivalent of four servings of dairy each day - for five years. When the study started, researchers believed calcium supplements might cut the rate of heart attacks and strokes.
However, the reverse was found, with preliminary figures showing a 40 per cent increase in the risk of heart attacks from the women who took calcium. Thirty-six women on calcium supplements had heart attacks, compared with 22 on the placebo. Some women died from cardiac-related illnesses during the trial, but none of them was believed to have been caused by the calcium supplements.
Osteoporosis New Zealand declined to comment on the results of the study.
Professor Ian Reid of Auckland University's faculty of medical and health sciences told the Herald on Sunday that while the study did not necessarily prove that all calcium supplements caused heart attacks, he was concerned about the "worrying trend". He believed the results were internationally significant.
Reid said three smaller international studies had shown similar results, which suggested the university's results were more than just a statistical anomaly. "That, in the context of what we have found here, we think is quite worrying."
People with heart disease developed a buildup of calcium in their heart vessels, so taking extra calcium could potentially speed that up, Reid said.
He had since written to all the women in the trial informing them of its findings. Those who had heart problems or poor kidney function had been advised to look at other ways of preventing osteoporosis.
"If you are elderly and you have heart disease probably you should be looking after your bones in other ways than with high calcium intakes," he said.
For others, his advice was to perhaps cut their daily calcium intake to around 500mg a day.
Facts At A Glance
Osteoporosis is a debilitating disease in which bones become fragile and more likely to break. If not prevented or if left untreated, osteoporosis can progress painlessly until a bone breaks. These broken bones, also known as fractures, occur typically in the hip, spine, and wrist.
Women are four times more likely than men to develop the disease - but men also suffer from osteoporosis.
Around 300,000 New Zealanders suffer low bone density or other symptoms of osteoporosis.
Calcium is essential for many body functions, including regulation of the heartbeat, conduction of nerve impulses, stimulation of hormone secretions and clotting of blood, as well as for building and maintaining a healthy skeleton.
With New Zealand's ageing population, the number of people with osteoporosis-related fractures is expected to rise dramatically in the next 10 to 20 years.
