The majority of Americans and Canadians are getting enough vitamin D and calcium to meet their needs, says a new report from the Institute of Medicine. Most people up to age 70 need no more than 600 international units, or IUs, of vitamin D per day, and those 71 and older may need as much as 800 IUs, the report finds. The amount of calcium needed ranges, based on age, from 700 to 1,300 milligrams per day.
A large amount of evidence reviewed by the committee that wrote the report confirms the roles of calcium and vitamin D in promoting skeletal growth and maintenance and the amounts needed to avoid poor bone health. The committee also reviewed hundreds of studies and reports on other possible health effects of vitamin D, such as protection against cancer, heart disease, autoimmune diseases, and diabetes. While these studies point to possibilities that warrant further investigation, they have yielded conflicting and mixed results and do not offer the evidence needed to confirm that vitamin D has these effects.
Sunlight triggers the natural production of vitamin D in skin and contributes to people's vitamin D levels. Individuals' sun exposure varies greatly, however, so the committee assumed minimal exposure to establish the intake values. The new intake levels for vitamin D cover the needs of individuals who get little sun.
Getting too much calcium from dietary supplements has been associated with kidney stones, while excessive vitamin D can damage the kidneys and heart. Evidence about other possible risks associated with routine vitamin D supplementation is still tentative, but some signals suggest there are greater risks of death and chronic disease associated with long-term high vitamin D intake. The report also set upper intake levels, which represent the upper safe boundary rather than amounts people should strive to consume. The upper intake levels and the amounts people require based on age and gender are detailed at www.iom.edu/vitamind.
Confusion about the amount of vitamin D necessary to ward off deficiency has arisen in recent years as tests that measure blood levels have become common. The measurements of sufficiency and deficiency that laboratories use to report test results are not standardized and different labs use different cutpoints. There may be an overestimation of deficiency because many labs appear to be using cutpoints that are higher than the evidence indicates are appropriate.