TORONTO (Reuters) -- As winter gets closer, the days get shorter -- and along with a shortage of light, many North Americans may also find themselves short of vitamin D, a potential cancer fighter.
A study released this week showed a connection between the sunshine vitamin, so-called because sunlight is our main source, and cancer prevention. It's the latest indication that people deficient in the vitamin may be at higher risk for a variety of health problems, including cancer.
Vitamin D is a fat-soluble vitamin that is found in fish oil, but most of our food sources -- chiefly milk -- are fortified with the vitamin. That's important because people living at higher latitudes, as in Canada and parts of the United States, don't have access to strong sunlight from about October to early March. As a result, a lot of people are deficient in the vitamin, said Joan Lappe, a professor of nursing and medicine at Creighton University in Omaha, Nebraska.
Lappe said a low vitamin D intake of about 200-400 international units (IU) -- the recommended daily dosage in the United States and Canada is about 200 IU for adults - is enough to help prevent some symptoms of deficiency, such as bone-related problems. But much higher levels may provide benefits for the prevention of cancer and other diseases, she said.
The Canadian Cancer Society agrees. It recently broke with Canada's public health policy on nutrition, which is aligned with the United States, to recommend people with light skin take 1,000 IU of vitamin D daily, through supplements, during fall and winter. People with darker skin, people who spend little time outside, and those who follow a cultural or religious dress code that requires they cover most of their body should take that amount year-round.
"We're recommending 1,000 IUs daily because the current evidence suggests this amount will help reduce cancer risk with the least potential for harm," said Heather Logan, director of Cancer Control Policy at the Canadian Cancer Society, in a statement announcing the decision. "More research is needed to clearly define the amount of Vitamin D that will maximize health benefits."
The Canadian Cancer Society made the recommendation in June, after the publication of a large placebo-controlled study led by Lappe that found a group of women taking 1,100 IU of vitamin D daily showed a substantial drop in cancer risk.
The women in the study, published in the American Journal of Clinical Nutrition, were given the higher dose of vitamin D over a four-year period. The group taking the supplement had a 60 percent lower cancer incidence than the placebo group. When the women who developed cancer during the first year were removed from the results, a 77 percent reduction in cancer incidence was seen, Lappe said.
Vitamin D experts in the United States also want to see more research into the vitamin's benefits, Lappe said. Last month, the Canadian Cancer Society contacted organizations like the U.S. National Institutes of Health and the National Cancer Institute of Canada to call for a large clinical trial using dosages of at least 1,000 IU to determine the amount required for cancer prevention.
"I have to commend the Canadian Cancer Society," Lappe said. "They're right out in the lead there on changing the recommendations to 1,000 IU a day. I was pretty impressed."
Determining the levels of vitamin D deficiency in the general population is also important, said Dr. Kenneth H. Cooper, chairman and chief executive officer of the Cooper Aerobics Center and Cooper Clinic in Dallas. His clinic now regularly tests for vitamin D in patients, he said, and deficiencies are common.
"Something as simple as vitamin D, and apparently as safe as vitamin D, personally, I think has tremendous potential in the future," Cooper said. "But we need more good, solid, double-blind clinical trials. Observational trials are good, but very few of them are double-blind clinical trials. And that's what we need more than anything else before we can strongly recommend regular use of vitamin D, particularly at the higher levels."
A group of leading vitamin D scientists called for an upper limit of 10,000 IU in a paper published in American Journal of Clinical Nutrition earlier this year, and studies have shown that dosages up to that limit appear to be safe, Lappe said. At his clinic, some patients are given very high dosages if they are especially deficient in vitamin D, Cooper said, and higher doses can quickly raise a person's blood levels of the vitamin without adverse effects.
But future recommendations on vitamin D intake may not be as simple as picking a new number and applying it to the population across the board, Lappe said, because so many factors can affect levels in the blood.
"I don't think there's going to be something that comes out that says everyone should take 1,500 IU a day," Lappe said. "I don't think it's going to be that simple. I think the answer will be measuring the blood levels of vitamin D to see where an individual stands."
Getting that dosage from food would be quite difficult - to get 1,000 IU from milk, you'd have to drink 10 glasses a day. Sunlight can provide a good dosage during the summer when much of the skin is exposed, but this isn't an option for most North Americans year-round, and concerns about UV exposure and skin damage or cancer are also a factor.
"Supplementation is the safest and most inexpensive way of getting vitamin D," Lappe said. Vitamin D supplements are inexpensive and easy to make -- they're produced using the lanolin from sheep's wool. People buying supplements should look for those containing vitamin D3, which is more effective than vitamin D2.
"Even if we don't get the big, definitive studies," Lappe said, "it would be interesting for people to just start taking (supplements) and see if in 10, 15 years from now we get a decrease in the instances of cancer as well as some of the other major chronic diseases."