Organization lobbying medical research agencies in North America to find out what dosage, if any, prevents the disease
Society officials don't think the organization has ever before indicated to the research community in such a high-profile way the need for a clinical trial. The move reflects a recent flurry of scientific papers that have come to the surprising conclusion that half of cancers, or even more, in a country like Canada could be prevented if all adults are encouraged to take the "sunshine vitamin."
If further experiments bear out the tantalizing findings, it would mean that vitamin D could be a magic bullet for cancer prevention on par with tobacco control, healthy eating and active lifestyles.
Heather Logan, the society's director of cancer control policy, said the organization acted because it thinks the vitamin may offer a way to "make dramatic inroads in terms of the burden of cancer."
But the society says scientific uncertainties hamper the current understanding of how to use it. Researchers have not yet run the kind of large-scale experiments that would uncover the levels people needed, and how doses would have to be adjusted for variable factors, such as a person's skin colour.
"The body of evidence around the impact of vitamin D ... now requires the rigours of a comprehensive research program to address the gaps in knowledge," the society said in the letter, sent last week.
Determining whether vitamin D prevents cancer is particularly important for Canadians. People in high latitude countries such as Canada cannot make it the natural way, by exposing naked skin to strong sunlight for about half of each year.
That is because sunlight doesn't get intense enough in northern areas of the world from about now until early March for production of the vitamin.
Researchers have found that during this so-called vitamin D winter, levels of the nutrient in people's bodies plunge, which they theorize increases vulnerability to cancer and other serious ailments. Most cells in the body - including those from such areas as the colon, prostate and breast - have receptors for the vitamin, suggesting it's needed for proper functioning.
A large trial would probably need thousands of participants, take years to complete, and cost millions of dollars. However, if the experiment confirmed dramatic health benefits, it could ultimately save governments and health insurance companies billions of dollars.
Besides the society, the letter was endorsed by a section of the World Health Organization that deals with sun protection and the American College of Rheumatology.
Among others, the letter was sent to the National Cancer Institute of Canada, the U.S. National Institutes of Health and the Canadian Institutes of Health Research, bodies that have available government and other funding for medical studies.
The letter has received a positive response. "There is enough evidence around to suggest that vitamin D ... could be of interest in terms of reducing cancer," said Phil Branton, scientific director of the Institute of Cancer Research at the CIHR.
The society said any experiment would need to use at least 1,000 international units of vitamin D a day to be clinically relevant. This amount is up to five times higher than Health Canada recommends. The society suspects the federal guideline, developed in 1997, needs to be raised. It said researchers should also look at health risks of taking vitamin D above Health Canada's 2,000 IU daily safety limit.
The society recommended that any experiment include people from a variety of backgrounds, because blacks and South Asians, who have more protection against ultraviolet light, are most at risk of having low vitamin D levels.
Medical researchers welcomed the cancer society's call.
Reinhold Veith, a University of Toronto professor in the department of nutritional sciences, said the investigation is needed because of the vitamin's low-cost and wide availability and the plausible scientific basis for why it might work at the cellular level.
"In terms of all of those features, I don't think there is anything else that can beat the vitamin D story," he said.
Researchers began investigating vitamin D because of the finding that those with low levels in their bodies were most likely to develop cancer. Frank Garland, a professor at the department of family and preventive medicine at the University of California in San Diego, published a study in August suggesting that the vitamin could prevent half of breast and colon cancers in North America.
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The D list
A chronology of vitamin D and cancer prevention:
1941 A U.S. researcher postulates that something about strong sunlight prevented cancer, based on observations of a south to north trend of increasing mortality for many cancers in North America.
1980 U.S. researchers Cedric and Frank Garland issue the hypothesis that low levels of vitamin D play a role in causing colon cancer. They found an inverse relationship between the amount of sunlight and colon cancer mortality in the United States. The finding touches off 15 years of research that suggests vitamin D insufficiency plays some kind of a role in many other cancers, including breast, prostate and ovary.
1997 A report on vitamin D for Health Canada and the U.S. Dept. of Health dismisses as "premature" the idea "that vitamin D deficiency increases cancer risk." It calls for more studies to test the hypothesis.The report sets the current recommended vitamin D intake standard for Canada and the United States based on the low vitamin D levels needed to prevent rickets and bone health.
June, 2007 U.S. researchers at Creighton University in Nebraska find that vitamin D supplementation of 1,100 international units daily reduced the relative risk of cancer in a group of women by 60 per cent. It is the first clinical trial to find such a result. Their study is criticized because it had a small number of participants and was originally designed to look at bone health.
The Canadian Cancer Society recommends 1,000 IU of vitamin D a day during fall and winter as a cancer preventive for those with white skin. It says blacks should take 1,000 IU year round.
October, 2007 The Canadian Cancer Society calls for a large clinical trial to find out the best vitamin D dose for cancer prevention.
Martin Mittelstaedt
