New Guidelines for Vitamin D and Calcium

If you've been confused about the flip-flopping reports on the benefits and risks of vitamin D recently, you're not alone. Health officials were just as baffled about the potential benefits that supplements of vitamin D and calcium could have, as well as how much of the nutrients would be sufficient to improve health.

That's why the Institute of Medicine (IOM), an advisory group established by Congress, was charged by the U.S. and Canadian governments to gather the existing evidence on the health benefits of vitamin D and calcium, and come up with revised guidelines to help the public and the medical community determine the recommend dietary allowance, or RDA, of each nutrient. And according to the committee's analysis, North Americans are not nearly as deficient in vitamin D as we have been led to believe.

The 14-member IOM committee, made up of nutrition and other experts, issued its report on Tuesday, advising that the average adult needs about 600 IU of vitamin D daily, and about 1,000 mg of calcium each day to maintain bone health. Those 71 years or older, however, may need more vitamin D, up to 800 IU a day, to combat deteriorating bone. Because of the lack of sufficient data to date, advice on vitamin D up to this point was not considered as a recommended dietary allowance, which is based on stronger scientific evidence, but rather an adequate intake suggestion, and stood at anywhere from 200 IU to 400 IU for adults. The new recommendations are based on data from more than 1,000 studies, most of which included trials in which volunteers were randomly assigned to receive either vitamin or calcium supplements or a placebo, after which their health outcomes were compared to one another.

In addition, the report states that contrary to previous claims, most Americans are not lacking in vitamin D, and that the majority of adults are in fact well-supplied with the bone-building vitamin. The discrepancy can be traced to the lack of standardization among labs that test for blood levels of the vitamin. Different facilities establish varying thresholds for what they consider to be sufficient levels of vitamin D and that can lead to a misleading perception that more people are deficient.

After studying data on which levels of vitamin D are linked to the most benefit for preventing fractures and maintaining bone health, the IOM committee determined that a blood level of 20 nanogm/mL was sufficient for the average adult. The mistaken belief that Americans are deficient in vitamin D has led some experts to suggest that adults spend more time in the sun, since UV exposure can trigger vitamin D synthesis in the skin. But the committee cautions against that practice, since UV exposure can increase the risk of skin cancer and that risk outweighs the need to boost vitamin D production in the body.

The committee's advice also applies only to nutritional requirements to maintain skeletal health, and should not, says committee member Dr. JoAnn Manson, be interpreted to suggest benefit for any other health condition. In recent years, studies have suggested a link between vitamin D supplementation and a lower risk of heart disease, as well as prevention of cancer, Alzheimer's, diabetes and autoimmune conditions. But after a thorough review of the existing evidence for those diseases, the committee determined that the data on such supplementation and non-bone conditions was “inconsistent, inconclusive as to the cause and effect, and insufficient to inform nutritional requirements,” says Manson. Most of the data drawing these correlations did not come from rigorous clinical trials that randomly assigned subjects to a vitamin or placebo group.

That's not to say that vitamin D will not at some point prove effective in preventing or alleviating conditions other than bone-related fractures; Manson is currently recruiting for a multicenter study, the Vitamin D and Omega-3 Trial, or VITAL, that aims to do just that. VITAL will involve more than 20,000 healthy subjects who will be taking either vitamin D or a placebo and then followed over a number of years for their risk of developing cancer, stroke and heart disease.

VITAL will be the first such large-scale randomized study to analyze vitamin D supplementation in this scientifically validated way, so until those results are released, in another five years or so, the IOM committee declined to make any recommendations about vitamin D's role in anything other than promoting bone health.

The committee also established upper limits of intake per day, since some studies suggest that megadoses of the vitamin D may not provide any additional benefit, and may actually cause harm. Even when it comes to bone health, for example, a recent trial showed that high doses of vitamin D supplementation did not lower the rate of fractures and other studies showed high levels of D increased the risk of kidney stones and other renal conditions. “This perception that more is better and that everyone should jump on the bandwagon of high doses of vitamin D is of concern until we have evidence from randomized clinical trails that the benefits of such dosing outweighs the risks,” says Manson.

The advice is not likely to be the last word on vitamin D and calcium supplementation, and as new data emerges on the role that these nutrients may play in warding off disease, the guidelines may change. But in the meantime, the evidence is strong enough to support supplementing the diet with vitamin D in order to keep bones healthy. Having an RDA for vitamin D, say experts, should help to clear up some of the confusion over D.



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