Calcium supplements: Can they raise a woman’s heart attack risk?

Calcium is important to bone health, but most people don’t get enough of it. That’s why supplements are recommended. A recent report links calcium supplements to an increased risk of heart attack. But do these findings hold weight?

A New Zealand team recently published a British Medical Journal meta-analysis questioning the safety of calcium supplements. Anna Kalynych, M.D., an interventional cardiologist, helps to define “meta-analysis,” a key aspect of this study. “A meta-analysis is way to pool a number of different studies to try and obtain numbers large enough to be able to formulate some sort of conclusion that you couldn’t formulate if you were just doing the individual study analyses alone,” she says.

This meta-analysis found a \~30% higher risk of heart attack in women taking calcium supplements. It showed no impact on stroke risk or overall cardiovascular outcomes. “While a 30 percent increase in risk sounds staggering, it does need some explanation, because it is a relative risk,” says Dr. Kalynych.

“Essentially what it means is if you compared those taking a placebo (sugar pill) versus calcium supplements alone, there would be five extra heart attacks for every 1,000 people taking the calcium supplements, based on this meta-analysis.” However this study has its flaws: patients in the British Medical Journal took only calcium, not combined vitamin D supplementation.

An earlier meta-analysis in the Annals of Internal Medicine reviewed data from 17 studies. It examined three key outcomes:
1) Calcium supplement use alone
2) Vitamin D supplementation use alone
3) A combination of the two 

This study found that calcium supplements alone had minimal, if any, effect on increasing cardiovascular risk. Vitamin D supplements, at moderate to high dose, appeared to protect against it.

So what conclusions should be drawn based on these conflicting accounts? If you’re at high risk of heart disease, talk to your doctor and prioritize getting calcium from your diet. If you’re at risk for osteoporosis or have low vitamin D, consider a supplement. Taking vitamin D with calcium may help. Support bone and heart health by exercising regularly, avoiding smoking, and limiting alcohol and caffeine.

UPDATE:

The British Medical Journal study reexamines links between calcium supplements and heart risks. Dr. Mark Boland and colleagues from Auckland, Aberdeen, and Dartmouth studied the risks of calcium supplements alone. Their research focused on women taking calcium without vitamin D. These authors found a slight increased risk of heart attacks in women taking calcium supplements alone.

Women’s Health Initiative data shows a modest rise in heart risk with calcium and vitamin D. Women who started calcium and vitamin D had a 13–22% higher risk of heart issues. Risk was lower for those already taking them or on placebo.

Women already taking calcium and vitamin D before the trial had no increased heart attack risk. The authors suggest this may be due to a sudden rise in blood calcium levels. This change could be linked to the slight increase in heart attack and stroke risk. It's important to remember women in the initial Women's Health Initiative study were older and had ongoing cardiovascular risk factors. So what should a woman consider out of all this?

• Clearly most women should get calcium primarily from diet, since high-calcium foods are beneficial and have never been shown harmful.
• If you’re not getting enough calcium or vitamin D, consult your doctor. Supplements alongside a healthy diet may help.
• None of us believe that we have enough evidence now to tell women who are already taking supplementations to stop.

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