The Canadian Cancer Society's decision to recommend to the entire adult population of Canada to begin taking vitamin D supplementation is a first for a cancer agency.

The Society made the decision because of the growing body of evidence about the vitamin's documented effect on lowering cancer incidence.

The most recent evidence emerged this week: a U.S. study showing that women who took vitamin D had a 60 per cent lower risk of developing breast, colon and other cancers.

"We are monitoring the evidence and believe there is a real role for vitamin D to reduce our risk for cancer and so far there are very few side effects," the Cancer Society's Heather Logan told CTV News.

"There are pieces of the puzzle that are progressively being put together and the puzzle isn't falling apart... it's getting stronger," agrees Dr. Reinhold Vieth, a researcher at Toronto's Mount Sinai Hospital.

The Canadian Cancer Society is now recommending that:

• Adults living in Canada should consider taking vitamin D supplementation of 1,000 international units (IU) a day during the fall and winter.
• Adults at higher risk of having lower vitamin D levels should consider taking vitamin D supplementation of 1,000 IU/day all year round. This includes people who are older; with dark skin; who don't go outside often, and who wear clothing that covers most of their skin.
• At this time, the Canadian Cancer Society does not have a recommendation for vitamin D supplementation for children.

The advice is important for Canadians, who typically get nowhere near enough vitamin D from our diet or from the sun.

"Because of our country's northern latitude, the sun's rays are weaker in the fall and winter and Canadians don't produce enough Vitamin D from sunlight during this time," Logan said.

While some experts say the recommendations are premature and that more studies are needed, others call the move groundbreaking.

"I think this is an important and historic step in the right direction. I think it will offer leadership in the world... as Canada will be the first country in the world to adopt this public health recommendation," said Dr. Cedric Garland, professor at University of California, San Diego, Department of Family and Preventive Medicine and Moores Cancer Center.

Dr. Colin Cooper of the Institute of Cancer Research in London, England, thinks other countries may follow Canada's lead.

"The weight of the evidence suggests that reasonably high levels of vitamin D can protect against cancer, so I think it is a prudent decision," said Cooper.

If the recommendations are adopted, Canada would begin a fascinating national experiment to see if raising our vitamin D intake could cut cancer cases in the future.

"Over time, this finding has the potential of eliminating a quarter of a million cases of cancer in North America annually and about 100,000 deaths from cancer annually," Dr. Garland said.

"Once people start taking a lot more vitamin D, you'll probably, in five years, see lower cancer rates and you will wonder why," says Vieth.

With a report from CTV medical specialist Avis Favaro and medical producer Elizabeth St. Philip