Placebo-controlled studies show people over 50 who take vitamin D supplements have a lower overall risk of premature death, a University of Toronto professor says. (Mark Gollom/CBC)

Some consumers and doctors are becoming convinced vitamin D can help reduce the risk of a long list of diseases, despite a lack of gold-standard research proving it.

A growing body of research suggests that supplements of the so-called sunshine vitamin may reduce the risk of multiple sclerosis, diabetes and breast and prostate cancers.

But much of the research comes from observational studies rather than placebo-controlled trials — the highest standard in health research. Such rigorous trials to prove vitamin D's preventive benefits are expensive, and since vitamins can't be patented, pharmaceutical companies have no financial incentive to do the research.

But there is a lot of circumstantial evidence. Many of the diseases on the list are more common farther north, so vitamin D seems the most logical explanation, said Reinhold Vieth, a nutritional science professor at the University of Toronto and an international authority on the vitamin.

Placebo-controlled studies have shown that people over 50 who take the supplements have a lower overall risk of premature death, Vieth said.

"There's only an upside," Vieth said of vitamin D. "The only thing it costs you is a little bit of money out of your pocket and the extra effort to take it."

Jamieson Laboratories' plant in Windsor, Ont., is racing to keep up with demand for the supplement.

Company president Vic Neufeld said that in dollars, "we're trending at about a 50 per cent growth rate" year over year. The growth rate is more than 60 per cent in terms of units of vitamin D, he said.

Until there is more proof of the benefits, however, health authorities remain cautious about the supplements.

While Vieth believes health authorities may eventually recommend 4000 IU, or international units, a day, the Canadian Cancer Society currently suggests 1000 IU, and Health Canada advises 400 IU, but only for people over age 50.

Health Canada and the U.S. Institute of Medicine are jointly studying the latest science to review recommended intakes for vitamin D and calcium.