Experts are increasingly pushing for higher daily recommended intakes of vitamin D, saying that while current amounts may prevent signs of deficiency, they are insufficient to provide a protective benefit against cancer.

Vitamin D is an essential nutrient produced by the body when ultraviolet radiation from sunlight strikes the skin. In northern latitudes, however, when sunlight is dim for significant parts of the year, many people cannot get enough sun to synthesize sufficient levels of the vitamin. This problem is particularly pronounced among those with darker skin. Few foods are rich in vitamin D. Fish oil and fortified food sources, such as milk or non-dairy milk substitutes, provide the most common dietary sources.

The United States and Canadian governments recommend a daily vitamin D intake of 200 IU. But vitamin D and cancer experts warn that this value is far too low.

Recently, the Canadian Cancer Society advised that light-skinned people take a 1,000 IU vitamin D supplement daily during fall and winter months, and that dark-skinned people or those who regularly keep all their skin covered while outdoors take a supplement year-round.

"We're recommending 1,000 IU daily because the current evidence suggests this amount will help reduce cancer risk with the least potential for harm," said Heather Logan, director of the society's Cancer Control Policy.

"I have to commend the Canadian Cancer Society," vitamin D researcher Joan Lappe said. "They're right out in the lead there on changing the recommendations."

Lappe was lead researcher in a recent study that found that women taking 1,100 IU of vitamin D per day showed a 60 percent reduced risk of developing cancer than women taking a placebo. Excluding women who developed cancer during the first year of the four-year study, the risk reduction from vitamin D was 77 percent.

In a paper published in the "American Journal of Clinical Nutrition," a group of vitamin D experts recently advised that an upper daily limit of 10,000 IU be set for vitamin D exposure, making a break with the current, more cautious, government recommendations.