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Women have been told that they need more calcium to reduce their risk of osteoporosis and hip fractures, but how much more is enough? A new study says it's probably a lot less than you think, and as NPR's Nancy Shute reports, taking too many calcium supplements can actually cause other health problems.

NANCY SHUTE: It makes sense that women over 50 should be doing everything they can to avoid osteoporosis. It increases the risk of hip fractures, which kill 16,000 people a year and cripple many more.

But taking lots of calcium doesn't look like it's much help. A big new study in the British Medical Journal found no benefit from consuming more than 750 milligrams a day.

Eva Warensjo is an epidemiologist at Uppsala University in Sweden. She is the lead author on that studio, which followed 61,000 women.

Dr. EVA WARENSJO (Epidemiologist, Uppsala University): We didn't find, as you would think, the higher intake of calcium, the lower the risk of fractures and osteoporosis.

SHUTE: But that's not a huge surprise. Doctors in the United States have been saying pretty much the same thing for years. Harvard researcher JoAnn Manson is a principal investigator in the Women's Health Initiative.

Ms. JOANN MANSON (Researcher, Harvard University): More is not necessarily better, and moderate intake may be optimal. There may be a threshold effect where once you get to a moderate level of intake, there's no further benefit.

SHUTE: In fact, taking more calcium could be not just worthless, it could cause other health problems, such as...

Ms. MANSON: Kidney stones and possibly an increased risk of cardiovascular diseases found in some recent studies.

SHUTE: Last year, the Institute of Medicine said that women over 50 should aim for 1,200 milligrams a day whether or not they have signs of bone loss. That is higher than the amount recommended in Sweden and other European countries. Manson helped write that report, and she's not ready to say that number is too high.

Still, that doesn't mean that all women need supplements.

Ms. MANSON: This does not mean that women need to take calcium supplements containing 1,200 milligrams a day because, on average, close to 700 milligrams a day would come from diet.

SHUTE: So most American women are getting as much as the Swedish study recommended without taking any calcium supplements. But many people haven't gotten that message.

John Tongue is an orthopedic surgeon in Portland, Oregon. He's been operating on women with hip fractures caused by osteoporosis for more than 30 years. So when this new study came out, he asked his wife how many calcium supplements she's taking.

Dr. JOHN TONGUE (Orthopedic Surgeon): I interviewed my wife last night and found out that she's taking more than the recommended dose in the United States.

SHUTE: How much more?

Dr. TONGUE: She's taking 1,400 milligrams as a supplement, in addition to whatever calcium she has in a normal diet.

SHUTE: That's getting up there. But she's also exercising, which Tongue thinks is more important than calcium for keeping bones strong.

Dr. TONGUE: A brisk walk for 20 to 40 minutes a day would do much more to improve people's general health and reduce their risk of injury than taking more vitamins or other supplements, which are so common.

SHUTE: But all too often, he says, his patients look for the answer not in common-sense prescriptions like that but in supplements that come in a jar.

Nancy Shute, NPR News.

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