HEALTH -- November 30, 2010 at 12:00 AM EDT
New Guidelines Boost Vitamin D Recommendation for Bone Health
Daily vitamin supplements including Vitamin D, far right. Photo via Flickr user Bradley J.
A government report released early Tuesday raised the recommended amount of vitamin D that most American adults should consume from 200 international units to 600 international units per day. The report, which also examined calcium intake, said that that level of vitamin D, together with sufficient calcium, is necessary to keep people's bones healthy.
But the authors also found that despite a recent slew of headlines that have linked vitamin D deficiency to everything from heart disease to cancer, there isn't enough evidence to say that vitamin D affects anything other than bone health.
The report marks the first time since 1997 that the Institute of Medicine has considered dietary requirements for Vitamin D. The new guidelines are based on a review of nearly 1,000 studies of the vitamin. Committee Chair Catharine Ross, a professor of nutritional sciences at Penn State University, says that the new report incorporates much more information than the 1997 guidelines did.
The previous numbers were a "guesstimate," she says. "Now we're basing the numbers on much more solid data."
The report isn't a major surprise -- most experts had expected the IOM to raise the recommended daily dose for vitamin D. The American Academy of Pediatrics had raised its recommended intake for children to 400 international units in 2003, and some vitamin D proponents advocate levels as high as 1,000 international units per day.
"I think that it's conservative compared to what some people thought it was going to be, but I think they're good recommendations," says Michal Melamed, a vitamin D researcher at the Albert Einstein College of Medicine.
And Sundeep Khosla, an endocrinologist at the Mayo Clinic in Rochester, Minn., and the president of the American Society on Bone and Mineral Research, says: "It's more or less in line with what I've been telling patients for years, it just provides some clear numbers."
Vitamin D is produced in the body from sunlight and is also found in foods, including fish and fortified milk. It was once known mainly for preventing the bone disease rickets in children. In the past few years, though, it's become a hot topic among researchers -- scientists have linked lack of vitamin D to nearly every imaginable malady: cancer, diabetes, depression, heart disease, immune system health and others. Meanwhile, other studies have suggested that a significant percentage of the U.S. population suffers from vitamin D deficiency, as more people stay inside or slather on sunscreen when they're outdoors.
But Ross says that despite the new interest in vitamin D, there's little evidence that much of the population is vitamin D-deprived, or that vitamin D affects anything other than bone health.
"We've heard and read the same [news] reports," she says. "The committee went into this with a completely open mind. We reviewed the literature for about 25 potential health indicators and we looked at the data very carefully. What we found for all of the indicators except bone health is that there isn't consistent evidence."
In part, that's because there simply haven't been very many large, randomized clinical trials that have tested the effects of vitamin D. Instead, most of the research has been less-reliable observational studies.
"We need randomized clinical trials," says committee member Joanne Manson, a Harvard professor who is chief of preventive medicine at Brigham and Women's Hospital in Boston. Manson is leading a large, randomized study of 20,000 older adults that will look at whether vitamin D doses of up to 2,000 international units per day can protect against heart disease and cancer. "What was surprising was that there were no previous [large randomized] studies designed to test role of vitamin D in cardiology or cancer," she says.
Studies such as Manson's, and others, could inspire the IOM to revisit the vitamin D guidelines someday. Or, they could show that vitamin D has no effect on those diseases.
"We've been down this road before with high levels of other nutrients, like vitamin E or beta carotene, that looked promising," Ross says. "But when the randomized clinical trials were done, they didn't pan out."
Michael Holick, a professor of medicine and physiology at Boston University and a longtime proponent of vitamin D, was one of the first researchers to study vitamin D deficiency. He says that it's "incredibly important" that the new guidelines have raised the recommended intake level threefold, though it is still lower than he recommends to his patients.
The new report also increases the "tolerable upper intake level," or the amount of Vitamin D that can be taken without safety concerns, from 2,000 to 4,000 international units (at higher levels it can cause kidney stones or other kidney problems). Raising the tolerable upper intake level is also important, Holick says, "because it means food manufacturers can think about putting it in more foods."
Holick himself recommends to his patients, friends and family that they get at least 1,000 international units of vitamin D per day.
But Catharine Ross says that there's no evidence that getting more vitamin D than the recommended daily dose will have any health benefits.
"Our report really points out once again that more is not necessarily better, and that's a hard message for the public," she says "We think that more research is needed, but at present we can just see no evidence for any better outcome at a higher level."