The news about vitamin D just keeps getting brighter. As more and more studies roll in, evidence is mounting that higher levels of vitamin D can reduce incidence of osteoporosis; rectal, breast and prostate cancer; diabetes; and a host of other ailments. An increased intake of vitamin D has even been associated with lower mortality rates.

The supplement has been dubbed the “sunshine vitamin” because it is created naturally when skin is exposed to light with a ultraviolet index of at least three. That means that residents of northern latitudes may be more likely to have deficits of vitamin D. At this time of year, in particular, many Canadians will experience low levels of this important vitamin. People with dark skin tones are among those most at risk, since it takes longer for their naturally sun-protected skin to generate the vitamin.

To prevent vitamin D depletion, the Canadian Cancer Society recommended this past year that all Canadian adults take at least 1,000 international units a day during the fall and winter. Meanwhile, those with dark skin, older adults, people who don’t venture outside often or people whose clothing covers most of their skin should take this dose year-round.

Even 1,000 IU a day is probably too low to obtain all the disease-prevention benefits, says one leading experts on vitamin D. At the same time, however, there is no official consensus within scientific and health-prevention circles on the optimal dose of vitamin D, or the optimal blood-test level to aim for.

In other words, there’s a very good chance vitamin D will help prevent many diseases, but beyond osteoporosis, science can’t guarantee that — yet.

“In many ways, taking a decent dose of vitamin D is like deciding on the wisdom of an investment,” says Dr. Reinhold Vieth, a professor in the Department of Nutritional Sciences at the University of Toronto. “You have to base the decision for future good upon the never certain evidence of the past. One difference with vitamin D is that there is no downside risk.”

Vieth says there are so many different beneficial responses supported by medical evidence that even if some of those were to prove not quite true, there will be others that will strongly justify taking a vitamin D supplement. “It’s an evolving story,” he says.

While the evidence is strongest for the prevention of osteoporosis, the evidence is more circumstantial for cancer, Vieth says. The Canadian Cancer Society, in making its recommendation, pointed to a random clinical trial published in June 2007 in The American Journal of Clinical Nutrition. That study found that post-menopausal women taking 1,100 IU of vitamin D daily were at far lower risk of a cancer diagnosis four years after follow-up. Two other survey-based studies found that women who have a life history of more sun exposure, or high blood levels of vitamin D for other reasons, were at lower risk of developing breast cancer before menopause, especially if that history was during the teenage years.

Canada’s northern location was key in the Canadian Cancer Society’s decision to make the dosage recommendation. The American Cancer Society has not given similar advice.

“Where a person lives is one important factor in how much vitamin D he or she can produce from the sun,” says Heather Logan, director of cancer control policy for the Canadian Cancer Society. “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.”

The Canadian Dermatology Association, which has long warned against the increased risk of skin cancer associated with too much sun, has backed the decision by the Canadian Cancer Society. It recommends supplements with small amounts of sun exposure, as “the preferred methods of obtaining vitamin D.”

Now, researchers are busy looking for other potential benefits of this long-overlooked vitamin. In September 2007, an analysis of 18 random, controlled trials reviewed research involving 57,311 participants. The study, published in the Archives of Internal Medicine, found that people over the age of 50 who took at least 500 IU of vitamin D daily reduced their risk of death by 7%. In addition, high blood levels of vitamin D have been linked to a lower rate of multiple sclerosis.

@page_break@So, what’s the best way to get a vitamin D boost? Other than supplements, Vieth says, a Caucasian wearing shorts and a T-shirt can produce the equivalent of 10,000 IU of vitamin D in 20 minutes outdoors on a sunny summer day: 10 for the front of the body and 10 on the back.

Foods containing vitamin D include fatty fish and egg yolks, but vitamin D is also commonly added to foods, including dairy products, margarine, soy milk and even orange juice. But these provide the average Canadian with only about 200 IU of vitamin D a day.

Vieth also says you shouldn’t worry if you miss your daily vitamin D dose, since the vitamin stays in your body for a fairly long time. “You can take all seven days worth of vitamin D all at once, once a week,” he says. “It’s how my family does it.”

Newcomers from southern climates may find themselves at a higher risk for disease. Those with darker skin are at the highest risk, Vieth says, noting a recent study that shows black Ontario residents have an increased risk of diabetes. Another study shows Muslim women who dress very modestly found that their back pain improved with increased doses of vitamin D.

“I see it as an impending epidemic of various kinds of diseases,” Vieth says. “In future, we’ll be kicking ourselves for not having dealt with our lack of vitamin D sooner.” IE