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
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
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
