In light of emerging research on the benefits of vitamin D, the Canadian Cancer Society said Monday that Canadians could consider brief, unprotected exposure to the sun, increased dietary intake of the vitamin and the use of supplements.

Over the past 18 months, evidence has emerged suggesting that vitamin D may reduce the risk for colorectal cancer, breast cancer, prostate cancer, non-Hodgkin's lymphoma, multiple myeloma and other diseases such as multiple sclerosis.

Vitamin D, which is produced naturally in the body through exposure to the sun's ultraviolet rays, is more available in the summer than in the winter and in the south than the north, said nutrition researcher Reinhold Vieth of Toronto's Mount Sinai Hospital.

"There's a lot of cancers, in particular, you know breast cancer, prostate cancer and bowel cancer, that correlate with latitude," said Vieth. "Even the prospects, your future with that cancer, depends on which season of the year your cancer was diagnosed in."

Balanced approach

Since exposure to the sun carries well-established risks for increased skin cancer, cataracts and premature aging, people need to take a moderate, balanced approach, and not trade cancers for cancer, said Heather Logan, director of cancer control policy for the Canadian Cancer Society.

"Some limited exposure unprotected may in fact reduce your risk of disease," Logan told CBC Newsworld, adding people should still follow sun sense guidelines, such as not overexposing themselves between 11 a.m. and 4 p.m., and wearing sunscreen when the UV index is higher than three.

"At the moment, probably going back and forth from your house to your car will be sufficient to maintain optimum levels in Canada," said Logan. "We're not talking about an hour."

Current recommendation low

How much sun people need depends on age, skin colour, where you live, and the intensity of the sun — factors that influence how quickly vitamin D is produced.

Most experts believe the current recommendation of 400 units of vitamin D a day for people up to age 50, and 600 units daily for those over 70, is probably too low, Logan said, suggesting somewhere between 400 units and the upper safe limit of 2,000 units a day.

People may also increase their dietary intake by eating foods naturally high in vitamin D such as fatty fish like salmon, and eggs. Cow's milk is fortified with vitamin D in Canada, and some cheeses and yogurt contain vitamin D.

A new study coming out in June will help researchers and policy analysts to better understand the role of vitamin D in preventing cancer, but other questions remain:

  • What are the precise optimal levels of vitamin D levels in the blood to help reduce the risk of developing these chronic diseases?
  • What is the optimum vitamin D intake, either through foods or supplements?
  • What role does skin colour and where you live play in how well equipped the body is to synthesize vitamin D?

Given these factors, there won't be a one-size-fits-all approach to vitamin D recommendations, Logan said, but the society will provide updated information on its website as it becomes available.