We are constantly bombarded with conflicting headlines about nutrition and ads for products that promise to make or keep us healthy. Sorting out the truth from the hooey is an uphill battle, but science can help. A team of researchers have examined 10 common claims about vitamin D, and found that most of them lack evidence. They published their findings in the Journal of General Internal Medicine. 

Lead researcher Michael Allan is the director of Evidence-Based Medicine at the University of Alberta. He and his colleagues reviewed more than 80 studies on vitamin D, looking for support for claims that the vitamin can reduce cancer risk, treat arthritis, and more. The team was somewhat surprised by their results; "Even areas that we really thought there was good evidence for benefit early on, don't seem to be bearing out," Allan said in a press statement. In other words, we should rein in our enthusiasm for a "vitamin D panacea," as the authors call it. 

The results showed insufficient evidence for eight popular beliefs about vitamin D supplementation:

  • That it can treat depression;
  • That it can treat rheumatoid arthritis;
  • That it can treat multiple sclerosis;
  • That it can prevent respiratory tract infections;
  • That it lowers cancer risk and mortality;
  • That it reduces overall mortality;
  • That taking a higher dose is better; and
  • That healthy adults should get their vitamin D levels checked regularly.

The remaining two out of the ten beliefs tested were backed by some evidence. The researchers found that vitamin D supplementation can help reduce the risk of falls and the risk of fracture from falls in older people. But even those benefits are minimal, Allan says. 

“If you were to take a group of people who were at higher risk of breaking a boneso had about a 15 per cent chance of breaking a bone over the next 10 yearsand treated all of them with a reasonable dose of vitamin D for a decade, you'd prevent a fracture in around one in 50 of them over that time. Many people would say taking a drug for 10 years to stop one in every 50 fractures is probably not enough to be meaningful.” 

Now, just because something hasn’t been proved doesn’t mean it’s wrong. Allan says a lot of the existing vitamin D research was poorly done, and there hasn’t been much of it. It’s possible that, in the future, research will find enough evidence to support some of these claims. But right now, it just isn't there. 

For more myths and facts, check out the National Institutes of Health’s vitamin D web page.

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