As women age, they are commonly told to take a calcium supplement to prevent bone loss and fractures — but for some, that simple advice could lead to an increased risk of heart attack.

Many older women take calcium supplements to prevent thinning bones. But medical researchers at the University of Auckland in New Zealand have found that women who take 1,000 milligrams of calcium each day may have an increased risk of having a heart attack.

Though the findings don't prove calcium causes heart attacks, three other studies have noted the same trend, said Dr. Ian Reid, lead author of the study published in the British Medical Journal on Tuesday.

If 44 older women took calcium for five years, one would have a heart attack, Reid said. By comparison, 50 women would have to take calcium for five years to prevent one bone fracture.

"There is a bone benefit from calcium, but in relation to the heart risk, they are fairly evenly balanced — so I think it has to be carefully considered," he told CBC News Tuesday.

It's a judgment call, said Dr. Jonathan Howlett, a cardiologist with Halifax's Capital Health district. Patient history must be considered when deciding whether supplements would be beneficial, he said.

"If her main problem really was her bones rather than her heart, I could easily see myself saying 'Go ahead and take them,'" he said.

Both doctors said older women should talk to their physicians about whether they need calcium supplements. If the answer is yes, Reid suggested taking only 500 milligrams a day, not 1,000 milligrams.