A landmark new study is raising the tantalizing spectre that a simple and cheap vitamin supplement may offer a highly effective way of preventing cancer.

The research, published in the online edition of the American Journal of Clinical Nutrition, finds that a combination of vitamin D3 and calcium has a substantially marked effect on reducing cancer incidence.

The four-year study out of Creighton University in Nebraska found that women who regularly took vitamin D3 had a 60 per cent reduction in cancer infections compared to a group taking placebos.

The study followed 1,179 healthy, women 55 years and older from rural eastern Nebraska between 2000 and 2005. Participants were randomly assigned to receive 1400-1500 mg of calcium alone, or supplemental calcium plus 1,100 IU vitamin D3, or placebo.

The researchers studied only vitamin D3, which comes from animal sources and seems to be more active than vitamin D2, which is derived from plant sources.

Among the 288 women taking placebo, 20 developed breast, colon, lung or another form of cancer. Among the 445 women taking just calcium, 17 developed cancer. But among the largest group -- the 446 women taking vitamin D daily -- just 13 developed cancer.

"What we found is that a vitamin D supplement decreased the cancer incidence in postmenopausal women by about 60 per cent," lead investigator Joan Lappe, an associate professor of both medicine and nursing at Creighton University, told CTV News.

On the premise that some of the women who did develop cancer may have entered the study with undiagnosed cancers, researchers then eliminated the first-year results and looked at the last three years of the study. When they did that, the results became even more dramatic with the calcium/vitamin D3 group showing a startling 77 per cent cancer-risk reduction.

"The findings are very exciting. They confirm what a number of vitamin D proponents have suspected for some time but that, until now, have not been substantiated through clinical trial," said Lappe.

"Vitamin D is a critical tool in fighting cancer as well as many other diseases."

While the study was open to all ethnic groups, all participants were Caucasian, she noted. Lappe said further studies are needed to determine whether the results apply to different ethnic groups, to men, and to women of all ages.

This is not the first time that researchers have noted the health benefits of vitamin D. In February, two studies found that the vitamin was linked to lower rates of breast cancer and colorectal cancer. The "sunshine vitamin," as it's sometimes called, has also been shown to kill some cancer cells in laboratory experiments.

"There's a lot of evidence out there that populations in first world countries are deficient in vitamin D and if you give them more, we can prevent cancers and other diseases that have been reported to be prevented with vitamin D," said Lappe.

Humans can absorb vitamin D when ultraviolet rays from the sun trigger vitamin D synthesis in our skin. But because of our short summers in Canada and our latitude, most Canadians don't get anywhere near enough of it all year long.

That's why Dr. Reinhold Vieth, who has conducted numerous studies of vitamin D at Toronto's Mount Sinai Hospital, believes every Canadian could benefit from taking a vitamin D supplement.

"The vitamin D story is what I call a 'no-lose' proposition. Take it. You can only win," he told CTV News.

Cancer Society recommends vitamin D supplementation

Because of the growing body of evidence about vitamin D, for the first time, the Canadian Cancer Society is recommending a specific amount of supplementation for Canadians to consider taking. The 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 evidence is still growing in this area, but we want to give guidance to Canadians about this emerging area of cancer prevention based on what we know now," said Heather Logan, director of Cancer Control Policy with the Canadian Cancer Society.

"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 Logan.

"As we find out more we will update our recommendation."

Logan cautions Canadians about relying too much on getting vitamin D through exposure to sunlight.

"It's not a good idea to rely solely on the sun to obtain vitamin D," said Logan. "For some people, it's possible that just a few minutes of unprotected sun exposure every day could increase skin cancer risk."

The Cancer Society is not changing its SunSense guidelines, as skin cancer is the most frequently diagnosed cancer in Canada.

The Society recommends that people reduce their exposure to the sun, particularly between 11 a.m. and 4 p.m. when the sun's rays are the strongest. And use a sunscreen with a sun protection factor (SPF) 15 or higher and SPF 30 if you work outdoors or if you will be outside for most of the day.

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