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reality check

Vitamin D tablets are photographed in the Globe studio on March 26, 2015.Fred Lum/The Globe and Mail

A new Canadian study suggests that vitamin D might not be a powerhouse supplement capable of reducing the risk of multiple sclerosis, cancer, rheumatoid arthritis and other chronic health problems after all.

The new research offers yet more proof that vitamins and other supplements aren't as beneficial to health as marketing messages would have us believe.

The study, led by Michael Allan, a family medicine professor at the University of Alberta who focuses on evidence-based medicine, runs counter to the past decade's popular narrative that low levels of vitamin D are responsible for many forms of chronic disease. Those researchers believe that taking relatively large doses of the sunshine vitamin will ward off or slow progression of diseases such as multiple sclerosis, which plagues Canada, a country with limited sunlight in winter months.

It's a powerful theory backed up by some research. For instance, a 2014 study in the journal JAMA Neurology found MS patients with higher levels of vitamin D had slower disease progression and fewer symptoms.

But according to the new study, most of the research into the positive effects of vitamin D aren't sufficient proof because the studies were too small, had inconsistent results or had other biases.

Dr. Allan and his colleagues analyzed only the high-quality studies looking at the effects of vitamin D to see what the research says. They found that taking vitamin D supplements may slightly lower a person's risk of fracture (relative risk reduction of 10 to 15 per cent), particularly if a person takes more than 800 IU with calcium. The vitamin is also associated with a slightly decreased risk of death. But there is no good evidence that vitamin D supplementation reduces the risk of cancer, respiratory infections or rheumatoid arthritis. Similarly, there's no compelling evidence to suggest supplementation can help treat MS or depression.

"Therefore, enthusiasm for a vitamin D panacea should be tempered."

It's not just vitamin D. A growing body of high-quality research shows that many popular vitamins, minerals and herbal supplements don't seem to do any good and, in some cases, may even cause harm.

A 2013 editorial in the journal Annals of Internal Medicine concluded that "supplementing the diet of well-nourished adults with (most) mineral or vitamin supplements has no clear benefit and might even be harmful." It cited evidence from several large studies. For instance, one large study that followed men taking multivitamins to prevent cognitive decline found no evidence of a difference between those who took vitamins and those that didn't. The authors also noted that some studies have actually found that high levels of vitamins A and E are linked to an increased risk of death. For instance, beta-carotene (which the body converts to vitamin A) has been found to increase the risk of lung cancer in smokers. Mounting research also suggests that women who take calcium supplements of 500 milligrams or more a day are more likely to suffer a heart attack or stroke. Calcium from food (dairy, canned salmon, oranges) is not linked to an increased risk.

Although many of the marketing messages around vitamins and herbal supplements may sound appealing, the truth is that for the most part, Canadians aren't truly vitamin-deficient.

There are some exceptions, of course, and some instances where vitamins are vital.

Women of childbearing age should get 400 micrograms of folic acid a day. Folic acid is added to some flours and grains in Canada. It's also possible to get folate, the natural form of folic acid, from foods such as broccoli, asparagus, potatoes and avocados.

A 2012 Health Canada report said many adults don't get enough magnesium, calcium and vitamins A and D, and that "there is concern" Canadian adults aren't getting enough potassium and fibre.

But purchasing supplements isn't necessarily the answer. Rather, focusing on eating a more nutritious diet that contains plenty of fruits and vegetables can solve many of those potential deficiencies.