Calcium Intake: More Is Not Better

JoAnn E. Manson, MD, DrPH


June 17, 2011

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Hello, this is Dr. JoAnn Manson, Professor of Medicine at Harvard Medical School, Brigham and Women's Hospital. I would like to talk with you today about calcium intake and the increasing evidence that more is not better when it comes to optimal health.

Calcium has been in the news a lot lately. You probably have heard about the studies linking calcium supplements to an increased risk for cardiovascular events, vascular calcification, and kidney stones in the Women's Health Initiative Calcium/Vitamin D Supplementation Study.[1] Now a large prospective study from Sweden published in the British Medical Journal [2]indicates that even when it comes to bone health, more is not better for calcium intake.

The Institute of Medicine (IOM)[3] released dietary guidelines for calcium earlier this year, and the recommended dietary allowance (RDA) for calcium from a combination of diet plus supplements was set at 1000 mg a day for adult women until age 50 years and 1200 mg a day for women older than 50 years of age. The IOM also set a tolerable upper intake level of about 2000 mg a day for women in these age groups because of some concern about kidney stones and other health risks when calcium intake is very high.

The study that was just published in the British Medical Journal looked at the relationship between calcium intake and risk for fractures and overall bone health. This was a very large study: more than 61,000 women, followed for 19 years overall, had a total of more than 14,000 incident fractures and more than 3800 incident hip fractures. Specifically, the fractures were identified through a registry, so concern about reporting bias or recall bias was minimal. This study suggests that it's only the women who had the lowest intake of calcium, below about 750 mg a day, who had an increased risk for fracture, and then with increasing intake of calcium, evidence of further benefit for bone health and fracture reduction was very limited. A threshold factor or plateauing of benefit was suggested.

The women who had the highest intake of calcium (above 1100 mg a day) actually had a hint of increased risk for hip fracture. The bottom line of this study was that more moderate levels of calcium intake were best for bone health and that more was not better. We should be recommending more moderate intakes of calcium for our patients and not above the RDA of 1000-1200 mg a day total. Assuming that many women will get about 700 mg a day from dietary sources alone, many women may require no more than an additional 500-600 mg a day from calcium supplements. In contrast, many women are taking a very high dose of calcium, often 1200-1500 mg a day just from the supplements alone, and this could lead to very high total intake.

On the basis of the recent study in the British Medical Journal, as well as the overall totality of evidence, it seems that even for bone health, calcium in moderation is probably best. We may want to recommend that women try to get as much of their calcium as possible from dietary sources. Some of the best dietary sources are low-fat dairy products and leafy greens, fortified foods such as fortified fruit juices and cereals, and types of fish that have bones in them, such as sardines and canned salmon. It's probably best, wherever possible, to read the food labels that will help you understand the amount of calcium that's in the different food products and to recommend reading labels to our patients.

So bottom line, the recommendation is for calcium intake in moderation, being sure to add dietary calcium to the calcium from supplements, to ensure that the total calcium intake isn't too high. Evidence is increasing that more is not better when it comes to calcium intake.

Thank you very much for your attention. This is JoAnn Manson.


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