Interest in the purported health benefits of vitamin D has made it one of the most frequently popped supplements around, but a long-awaited report commissioned by the Canadian and U.S. governments says it is premature to take the sunshine vitamin in the hopes of warding off cancer, diabetes and other chronic diseases.
The report does advise a significantly higher intake for most people - 600 International Units, or three times current recommendations - to promote good bone health.
But it also says that research through drug-style clinical trials is needed to confirm the sensationalistic claims that have been made about the vitamin.
With the exception of vitamin D's well established link to promoting strong bones, taking the nutrient to prevent other conditions is "currently not supported by evidence that could be judged either convincing or adequate," it says.
The findings were to be released Tuesday by the Institute of Medicine in Washington, which oversaw the expert panel that conducted the evaluation. The report will be used by the two governments to review current advice on how much of the nutrient people need, the recommendations that are the basis of the ubiquitous labels contained on most food packaging. The report also recommends that children 8 and under consume more calcium.
Health Canada said in a statement: "The Government of Canada welcomes the new recommendations and will review them to assess the impact they may have on dietary guidance for Canadians. The review ... will begin immediately."
The new recommendation calls for everyone age one to 70 to take 600 IU of vitamin D a day, while those 71 and older should take 800 IU. At these intakes, 97.5 per cent of the population would have their needs for the nutrient met. The current guideline from Health Canada ranges from 200 IU to 600 IU, depending on age, although breastfed babies need 400 IU daily, a level the panel continues to endorse.
The panel's recommendations suggest that most people will need to take a multivitamin or other supplements, because diet is a poor source of the nutrient. Fortified milk, one of the most common foods containing the nutrient, has only 100 IU per cup.
The report is the first in-depth evaluation of vitamin D conducted by the institute since 1997, and follows a recent flurry of tantalizing scientific studies linking low blood levels of the nutrient to an array of serious conditions, including breast and colon cancers, heart disease, autoimmune ailments, and influenza.
Some of these studies have suggested that people need to take far more of the vitamin - doses of thousands of IU daily - to lower their risks of these diseases, findings that have led public health groups ranging from the Canadian Cancer Society to the Canadian Pediatric Society to urge people to take the vitamin.
The panel concludes that this call for high doses of vitamin D is premature, because it is based mainly on epidemiological studies. Epidemiology, the science of who gets diseases, has been involved in huge medical breakthroughs, such as the discovery that smokers are at higher risk of lung cancer, but doesn't offer conclusive evidence linking conditions to the nutrient.
The panel's main worry is that the supplement field is littered with previously hyped nutrients, ranging from beta-carotene to vitamin E, that were found to be useless or even harmful when subjected to drug-style clinical trials. It also calls for caution, because there is a hint in the current research that one type of cancer, of the pancreas, may be more common in those with the highest levels of vitamin D.
Nonetheless, the panel says it is safe for those aged nine and older to take up to 4,000 IU of the vitamin daily, double the current maximum intake level. If the recommendation on the new safe exposure is adopted by the two countries, it will make it easier for researchers to run drug-style trials on higher doses and settle the controversy over vitamin D.
The panel was composed of nutrition and vitamin experts from Canada and the United States, but didn't include any of the scientists who have been most vocal in supporting the role of the nutrient in a wide variety of chronic diseases.
The new recommendations of only 600 to 800 IU are a "health catastrophe," according to Cedric Garland, a professor of preventive medicine at the Moores Cancer Center at the University of California, San Diego.
Dr. Garland is one of the leading U.S. vitamin D researchers, and published the first studies showing that colon cancer is more prevalent in northerly areas, a strong hint that seasonal lack of vitamin D due to less wintertime sunshine is a trigger. He later duplicated the work with breast cancer.
"Vitamin D has the capability of preventing most cases of breast cancer, virtually all cases of bowel cancer," he said. "The idea that we're sitting back and allowing time to go forward without acting on these discoveries is extremely frustrating."
Dr. Garland says the panel should have set a daily dose of at least 2,000 IU. The case for taking more vitamin D is "as compelling as the case for the Salk polio vaccine or for any of the modern advances in medicine," he said.