Nutrition Action Healthletter spoke on the phone with Bess Dawson-Hughes, the director of the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University and a professor of medicine at Tufts. This is what she had to say about calcium and bone health.
Q: Why is calcium so controversial?
A: The controversy has been driven by two issues. One is the risk of kidney stones. In the Women’s Health Initiative—which gave 36,000 women 1,000 mg of calcium or a placebo every day for seven years—the women who took calcium had a 17 percent higher risk of kidney stones. But the average calcium intake of the supplement users was actually up around 2,100 mg a day. So they were way up there.
Q: Why did they get so much?
A: The women were allowed to take their own supplements along with the trial’s. Gary Curhan at the Harvard School of Public Health has reported repeatedly that the more calcium you get from food, the lower the kidney stone risk. But if you’re getting large amounts of calcium from supplements, you have a higher risk.
Q: So don’t overdo it?
A: Right. Calcium is essential for bone. It’s important to reach the Recommended Dietary Allowance, which is 1,000 to 1,200 mg a day. There is no known advantage whatsoever to getting more, and there appears to be a risk of kidney stones if you take supplements to go beyond the 1,200 mg.
So, stay put at the RDA. And that applies both to people who want to prevent bone loss and to those who already have osteoporosis.
Q: Does that mean taking 1,200 mg?
A: No. Many doctors were saying, “Take 500 to 600 milligrams twice a day,” without bothering to find out what people were getting in their diet. And we get more these days because many foods are fortified with calcium. There’s rarely a need for more than one of those 500-milligram supplements per day, if that.
Q: What else has caused controversy?
A: Researchers in New Zealand have repeatedly raised the issue that too much calcium increases the risk of cardiovascular disease. A German study found the same thing. But other researchers, in growing numbers, have seen no risk whatsoever. And that includes the big trials. I think the concern about cardiovascular disease risk is just a blip on the radar screen that we’ll soon forget.
Q: Did calcium takers in the Women’s Health Initiative have a higher risk of cardiovascular disease?
A: Some researchers claim that there was a higher risk, but, oddly enough, not in the women who got the most calcium.
When the U.S. research team that ran the study analyzed the whole data set, they saw absolutely nothing—not even a glimmer of risk.
Q: Have other studies found a risk?
A: A meta-analysis found a higher risk in people who took calcium supplements. But the data that swung the balance were from a UK trial that was designed for another purpose, and half of the participants stopped taking calcium two years into the five-year study.
How can you hang your hat on those data? Most researchers feel that this controversy is just a tempest in a teapot.
Q: Do trials show that calcium lowers fracture risk?
A: Not calcium alone. It’s an important component of a strategy to prevent fractures, but not a solo component.
Q: Have trials looked at fractures in women who get too little calcium?
A: Not usually. In our first big trial looking at bone density, we recruited women with low calcium intakes in two categories—either less than 400 milligrams a day or 400 to 600 milligrams a day— and gave them either calcium or a placebo.
Those with the very low intakes had a much better bone density response to calcium than did those with the higher intakes. But that trial measured bone density, not fractures.
Q: Why doesn’t calcium alone prevent fractures?
A: We don’t know, but when we did a huge meta-analysis a few years ago, we saw a hint that excessive amounts of calcium might increase the risk of hip fractures. If calcium supplements help people who ordinarily consume too little and harm people who consume too much, that may explain why you don’t see a benefit when you put all the data together. It’s complicated.
Use the chart below to see how much calcium certain foods have, so you can plan a healthy, calcium-rich diet.
Other relevant links:
- When to take one calcium supplement over another. See: Is Calcium Citrate a Better Mineral Supplement than Calcium Carbonate?
- Three studies have fueled confusion over calcium and heart disease. See: Calcium Confusion
- Shoot for recommended levels of calcium and vitamin D. See: Calcium and Vitamin D Revisited