Two major clinical trials are just beginning in the United States that will likely settle, once and for all, whether everyone living at northern latitudes should pop a vitamin D pill every day to help ward off cancer, heart disease, and a host of other serious ailments.
The trials will also test the benefits of calcium supplements and omega-3 fatty acids, two other nutrients that also have gained a widespread following over their purported health benefits.
Hopes are high that the research studies will end the debate over the sunshine vitamin because they will be using relatively high doses – 2,000 International Units – a day, and involve more than 22,000 people, a large enough group to uncover any benefits or risks.
Both trials have been designed specifically to test the nutrient’s possible role in preventing cancer, perhaps the most dramatic medical claim that has been made about the vitamin.
“We’re not going to change formal public policy [about taking vitamin D] until we have at least one randomized trial with a primary outcome being cancer,” says Joan Lappe, a professor at Creighton University in Nebraska, and the lead researcher on one of the trials.
Dr. Lappe’s review will involve 2,300 postmenopausal women, who will be tracked for four years to check whether the vitamin reduces cancer rates, along with the incidence of cardiovascular disease and diabetes. Some of the women will also be given calcium.
The other trial, which will involve 20,000 people, is being run jointly by Harvard Medical School and the Brigham and Women’s Hospital in Boston. It will also test the theory that fish oils are good for heart health and stroke prevention, and will run for about seven years.
Both studies are receiving funds from the U.S. National Institutes of Health.
Vitamin D has acquired its health-cult status because many studies have found that people with more of the nutrient circulating in their blood have lower rates of some cancers. As well, other research – based on epidemiology or the study of disease distribution in large populations – has found that there is more cancer, diabetes, and other chronic ailments among those living at northern latitudes than among people living further south.
This peculiar south-to-north pattern of increasing incidence of many diseases suggests a possible role for vitamin D because most of this nutrient is made in the skin when cholesterol in it is exposed to strong, ultraviolet light – hence the sunshine vitamin moniker.
Light isn’t intense enough to make the vitamin the natural way in northern countries like Canada for nearly six months every fall and winter, causing many people who aren’t supplementing to have seasonal deficiencies and possibly putting them at risk of illness.
While epidemiology has been suggestive of benefits from vitamin D – it was the research technique used to finger cigarettes as a cancer risk – it has the drawback of not constituting proof in the same way as a drug-style clinical trial involving some people taking medication and others a dummy pill, the gold standard for proving the efficacy of any treatment.
The idea that a vitamin deficiency may cause cancer and many other illnesses is also such an unconventional one that it has prompted disputes within the medical research community, with doctors who are skeptical arguing that before people start taking large amounts, physicians should be certain both of its efficacy and potential side effects.
The researchers involved in the trials are also urging caution.
“We have to be careful before jumping on the bandwagon to take megadoses of supplements before we have conclusive answers from randomized trials,” says JoAnn Manson, co-leader of the Harvard/Brigham study and a professor of medicine at Harvard Medical School.
Another factor suggesting a careful approach is that many nutrients, such as vitamin C and beta-carotene, once as hyped as vitamin D, failed to live up to initial, hopeful research after drug-style trials didn’t find the value in taking them, according to Dr. Manson.
But those who have been urging wider usage of vitamin D say the evidence is already compelling and that people shouldn’t wait for the trial results to start supplementing.
“People should not remain vitamin D deficient,” says John Cannell, head of the Vitamin D Council, a California-based non-profit group that has been advocating widespread use of the nutrient as a public health measure.
Dr. Cannell says that when it comes to vitamin D, physicians have an obligation to “act based upon what is currently known, not waiting for what is going to be known in the future.”
But Dr. Manson says that there may be early indications of the results from her research. For ethical reasons, those participating in the study will be monitored for both harmful effects and benefits, which if found, may cause the trial to be altered.
How much vitamin D should you take?
The doses used in the clinical trials checking vitamin D’s anti-cancer properties will be 2,000 International Units a day, Health Canada’s maximum safe level. This is the equivalent of two typical over-the-counter pills and is designed to raise blood levels of the nutrient to concentrations associated with lower cancer risk in previous epidemiological research.
The Canadian Cancer Society has been recommending 1,000 International Units a day, with whites taking that amount in fall and winter and those with dark skin year-round because non-whites don’t make the vitamin as quickly in Canada’s relatively feeble sunlight.
The cancer society made the recommendation following the publication of study in 2007, the first of its kind, finding that about 1,100 International Units taken daily had anti-cancer properties.
Health Canada says people need take only 200 International Units to 600 International Units a day, depending on age, a recommendation based on vitamin D’s well recognized role in promoting bone health.
There are very few dietary sources of the nutrient, making it hard to get large amounts from food. Fortified milk has 100 International Units per cup. Wild salmon is one of the best natural sources, at about 800 International Units per serving. Eggs contains about 25 International Units per yoke.
Previous research has found that a vitamin D intake of around 400 International Units per day doesn’t have anti-cancer properties.
