By Nathan Seppa, Science News
A scientific panel has called for tripling the recommended dietary allowance of vitamin D among people ages 9 to 50 and increasing the amount slightly for people older than that. The committee of scientists, convened by the National Academies' Institute of Medicine, also doubled the upper level of vitamin D that people that age can safely take in any given day from 2,000 international units to 4,000 IU.
The panel also bumped up calcium targets, a less controversial move. The report, requested by the U.S. and Canadian governments, was released November 30.
Vitamin D recommendations hadn’t been changed since 1997. And despite a wave of studies suggesting that the “sunshine vitamin” has benefits going far beyond bone health, the panel restricted its rationale to just that. Apart from aiding bone fitness, the panel said, the benefits of vitamin D “are currently not supported by evidence that could be judged either convincing or adequate.” The report authors cited a lack of cause-and-effect data from vitamin D studies of other purported benefits and said those studies didn’t clearly delineate the doses needed to achieve the benefits.
What’s more, the panel suggested that fears of vitamin D deficiency might be overblown. “Overall, the committee concludes that the majority of Americans and Canadians are receiving adequate amounts of both calcium and vitamin D.”
Vitamin D isn’t a true vitamin but rather a hormone made from skin cells when they are hit by ultraviolet radiation from the sun. Food cannot provide enough unless it is artificially fortified, such as milk. Because of vitamin D’s unique sunshine origin, randomized, controlled trials—the kind IOM noted are lacking—are nearly impossible to do because people cannot be kept out of the sun and their vitamin D levels are difficult to control, says Bruce Hollis, a nutritional biochemist at the Medical University of South Carolina in Charleston.
The report got a stern rebuke from some well-known vitamin D researchers, who see the increases as woefully inadequate. “This was a big waste of money,” says Hollis. “I agree with their recommendations for the first year of life,” he says, citing the panel's target of 400 IU for infants, a doubling from the previous recommendation. But he was puzzled that this recommendation didn’t extend to the children’s mothers. Despite outweighing infants by ten times or more, he says, women—and men—saw their vitamin D recommended daily intake set at only 600 IU for ages 9 to 70. People over 70 should get 800 IU a day, the panel said.
“Given the [panel’s] superconservative philosophical approach to decision making, the tripling of IU recommendations for people 9 to 50 is pretty good,” says Reinhold Vieth, a nutritionist at the University of Toronto.
But Vieth and others worry that the change won’t be heeded anyway. A person who is deficient in vitamin D could remain deficient getting these recommended amounts, says Michael Holick, a biochemist at Boston University. As a result, many people who are found to be deficient by their doctors will just get prescription supplements to boost their levels, he says.
“I don’t think this does anything to create confidence in IOM recommendations,” says endocrinologist Robert Heaney of Creighton University in Omaha, Neb.
The panel also increased the upper level of vitamin D intake for adults to 4,000 IU, doubling what is essentially the maximum safe daily dose. These new upper-end levels range from 1,000 IU for infants to 3,000 IU for 8-year-olds.
Holick says the new levels could allow some vitamin manufacturers to double the amount of vitamin D in their pills. And food manufacturers might find it easier to fortify products without worrying about pushing a consumer over the daily top-end level.
The IOM panel consisted of 14 scientists who met eight times and reviewed the relevant literature. Hollis openly questioned the composition of the panel. “Anybody who had ever expressed an opinion [on vitamin D] was not allowed anywhere near this committee,” he says.