Public health groups that have urged popping more vitamin D are sticking to their recommendations, even though the doses they suggest exceed - sometimes by substantial margins - the amounts deemed needed in a report by a blue-ribbon U.S.-Canadian panel.
Three high-profile public health organizations - the Canadian Cancer Society, the Canadian Pediatrics Society and Osteoporosis Canada - have issued advice over the past three years calling for increased consumption of vitamin D as a way to prevent chronic conditions such as cancer. Canada is one of the few countries in the world where so many prominent health advocacy agencies have taken such a stand.
The groups have suggested intakes ranging from 800 International Units a day to a high of 2,000 IU. That is substantially more than the amounts recommended by the panel, appointed by the U.S. and Canadian governments and convened by the Washington, D.C.-based Institute of Medicine.
In its report on Tuesday, it said most adults and children need only 600 IU a day, although it said taking up to 4,000 IU a day is safe. The panel also said the evidence isn't convincing enough to take the nutrient to ward off cancer, heart disease, diabetes and other chronic ailments that have frequently been linked in research to having too little vitamin D circulating in the blood.
The institute's levels "are targeting only bone health. We're going to continue with our recommendation around cancer prevention," says Heather Chappell, a spokeswoman for the cancer society.
The society has been saying since 2007 that whites in Canada need to take 1,000 IU during the fall and winter and non-whites that amount year round because their skin isn't as effective in making the nutrient in the country's weaker sunlight.
Osteoporosis Canada recommends people under 50 take up to 1,000 IU daily and those over 50 to take 800 to 2,000 IU. "We still have our recommendations that we stand by," says spokesman Matthew Rocheford.
The pediatric society calls for pregnant and lactating women to consider taking up to 2,000 IU a day. The society's medical affairs director, Danielle Grenier, said it will review the IOM report.
The decision of the groups to stick to their positions suggests that the long-running scientific controversy over the optimum dose of vitamin D is likely to continue until there are definitive, drug-style clinical trials that either substantiate or reject the numerous health claims that have been made.
Several of these trials are underway in the United States, but their results won't be available for years. The amount deemed necessary by the IOM panel is based on the quantity of the vitamin needed for strong bones, and represents a hefty tripling of the dose currently set by Health Canada for most adults. But it falls far short of what many of the advocates for vitamin D have been recommending.
To be sure, there are sharp divisions among researchers about vitamin D's possible ability to prevent cancer.
An extensive review by the UN's International Agency for Research on Cancer two years ago, for instance, concluded that there is a case for vitamin D cutting the risk of colon cancer.
"To us, that was a much more thorough review that was specifically looking at cancer risk and vitamin D," Ms. Chappell said of IARC's research.
But one of the Canadian scientists who worked on the institute panel - biochemist Glenville Jones of Queen's University in Kingston - says he was originally more supportive of the view of taking vitamin D to fight cancer, but concluded, based on a review of the scientific literature, that this position is far from proven.
Dr. Jones said Tuesday at a news conference in Washington on the IOM report that he was "quite amazed by the fact that it isn't nearly as clear cut as some of the advocates have suggested."