IOM Updates Dietary Intakes for Calcium and Vitamin D
How much vitamin D do you need? Depending on which experts or sources you consult, you could be urged to get anywhere between several hundred to several thousand international units (IUs) daily. While recommendations for the interrelated nutrient calcium do not vary as dramatically, some people -- particularly older women wanting to hedge their bets against osteoporosis -- heed advice to consume quantities well above the amounts that nutrition research deems necessary.
This clashing guidance has arisen from a profusion of new findings and ongoing research into these nutrients. Increased awareness of osteoporosis and its precursor osteopenia have heightened women's interest in getting enough calcium. Scientific papers have pointed to intriguing possibilities for vitamin D's role in several health concerns, including heart disease, cancer, and a variety of immunological disorders. Moreover, as tests that measure patients' vitamin D levels have become routine, stories of widespread deficiencies among Americans have stoked anxieties.
Besides, it just seems logical that if a base amount of an essential vitamin or mineral prevents disease, then higher doses would surely afford more protection. But when it comes to nutrients, you can get too much of a good thing.
A recent Institute of Medicine report brought some clarity to the vitamin D and calcium confusion. The report details how much of these two nutrients is required and the amounts at which risks arise. In short, most Americans and Canadians up to age 70 need no more than 600 IUs of vitamin D per day, and those 71 and older may need as much as 800 IUs. The amount of calcium needed ranges, based on age, from 700 to 1,300 milligrams per day.
These are amounts necessary to build and maintain strong, healthy bones. Proponents of higher amounts of vitamin D had hoped that the committee of experts who wrote the report would also identify amounts necessary to promote heart health and prevent cancer, among other health issues. However, the evidence about vitamin D's role in these areas is uncertain. Positive study findings -- and, consequently, the ones more likely to garner public attention -- are countered by negative findings, creating a mixed bag of evidence that did not allow the committee to draw definite conclusions.
The evidence shows many people are getting the necessary amounts of these nutrients through some combination of dietary intakes, supplements, and sun exposure in the case of vitamin D, the report says. This finding may set at ease the minds of many people worried that they are part of a deficiency "epidemic." A fundamental lack of agreement about blood test measurements underlies the reports of rampant vitamin D deficits, the report notes. Because there is not a standard measurement marking the point at which a person is deficient, different laboratories that process these tests use different cutpoints, including some that define deficiency at levels lower than the evidence shows are appropriate.
New research may eventually answer questions about the role of vitamin D in health areas besides skeletal health and also elucidate initial hints at potential harmful effects of long-term high doses of the vitamin. "Past cases remind us that some therapies -- such as high doses of vitamin E and beta carotene -- that seemed to show initial promise for treating or preventing health problems ultimately did not work out and even caused harm," said committee chair Catharine Ross. "This is why it is appropriate to approach emerging evidence about an intervention cautiously, but with an open mind."
-- Christine Stencel
Dietary Reference Intakes for Calcium and Vitamin D. Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, Food and Nutrition Board, Institute of Medicine (2010, 482 pp.; ISBN 0-309-16394-3; available from the National Academies Press, tel. 1-800-624-6242; $69.95 plus $5.00 shipping for single copies).
The committee was chaired by A. Catharine Ross, professor and Dorothy Foehr Huck Chair, department of nutritional sciences, Pennsylvania State University, University Park. The study was funded by the U.S. departments of Health and Human Services, Agriculture, and Defense, and by Health Canada.