As fall marches into winter and hauls us deep into flu season, some experts suggest a big dose of Vitamin D could help sidestep that lurking virus.

Vitamin D, also known as the sunshine vitamin, has a well-established role in helping to maintain strong bones. It’s now under the microscope for role it plays, when in short supply, in a range of illnesses, from heart disease to cancer, to autoimmune disorders and infections, including influenza.

Our bodies make their own vitamin D when we expose the skin to the sun’s UVB rays. But our long winters provide minimal sunshine and weak UVB rays, erasing the opportunity to synthesize this important vitamin for many months.

Health data released by Statistics Canada in 2010 reported about 10 per cent of the population, or 3 million people, had inadequate blood concentrations of vitamin D, and within that group, 1.1 million were outright deficient in vitamin D.

The U.S. Endocrine Society stresses the importance of vitamin D in maintaining health. It points out nearly every cell in the human body interacts with the vitamin, and that the activity of many genes — up to a third of the entire human genome — is affected by vitamin D.

To compensate for the lack of sunshine during the cold season, we can increase our intake of the few foods containing the nutrient, such as fatty fish, and those fortified with vitamin D, such as milk and orange juice, or we can take vitamin D supplements.

But although the Endocrine Society says evidence suggests vitamin D deficiency may increase the risk of many diseases, it stresses in a news release published last year that no hard evidence currently exists showing that taking vitamin D supplements prevents or treats illness beyond those that related to the bones.

“Why is there so little data on vitamin D and non-bone diseases?” the society asks.

It speculates the answer has to do with the fact that only recently have researchers realized that vitamin D is not harmful at new, higher doses, and few studies used enough vitamin D to raise blood levels to the required level.

In fact, how much vitamin D people should take is a controversy raging between policymakers and vitamin D advocates.

Last year, the Institute of Medicine (IMO) issued new guidelines based on the recommendations of a panel of experts in the field. The study, funded by both the Canadian and U.S. governments, tripled the daily dietary allowance to 600 international units (IU) a day from 200 IU a day, and set a daily ceiling of up to 4,000 IU.

These are also the current Health Canada recommendations.

The IMO’s report says evidence supports a role for vitamin D and calcium in bone health, but not in other health conditions. It says emerging evidence indicates too much of these nutrients may be harmful and challenges the concept that “more is better.”

Reinhold Vieth, a clinical biochemist at Mount Sinai Hospital, who has studied the nutrient for some 20 years, says whether we synthesize the vitamin in large doses via sunshine on the skin or we swallow a supplement makes no difference to how the nutrient behaves in our bodies.

Zoltan Rona, an MD who practices complementary and alternative medicine in Thornhill and author of Vitamin D, the Sunshine Vitamin (Alive Books) recommends 10,000 units a day to his adult patients.

In fact, with so little sunshine in our winters, adults won’t get much response from supplementation without taking at least 5,000 units a day, Rona says.

Vieth points out medical organizations such asOsteoporosis Canada, the Canadian Pediatric Association and the Endocrine Society recommend a daily dose of 1,200 units to 2,000 units.

Vieth recognizes policymakers have to take a cautious, conservative course, because their recommendations cover a spectrum of people and their guidelines stay in place for a long time.

“Canada is relatively aggressive,” Vieth says. “In the U.K., for people under age 60, there’s no policy, because, according to the government, there’s enough sunshine in Britain to provide sufficient vitamin D.”

The Vitamin D Council, a U.S. non-profit organization whose stated aim is to end the worldwide vitamin D deficiency “epidemic” through awareness and research, advises a two-pronged approach to guard against influenza.

It suggests taking on average 2,000 to 5,000 IU a day of vitamin D3 (the form of vitamin D produced by UVB rays on the skin) and getting a flu shot.

“Vitamin D may also reduce symptoms of influenza and reduce the risk of developing pneumonia following influenza. Vaccines strengthen the body’s ability to fight infection. Therefore, combining high levels of vitamin D and anti-influenza vaccines provide the best protection,” according to the Council’s web site.

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Vieth agrees with the council’s approach.

“Vitamin D is likely to make a difference; a flu shot is likely to make a difference. The public wants to know in black and white, but you can only go by probabilities.”

Flu myths

• You can catch the flu from the vaccine.

The vaccine is made from an inactivated virus that can't transmit infection. It takes a week or two to get protection from the vaccine, so people who get sick after receiving a flu vaccination were going to get sick anyway.

• Healthy people don't need to be vaccinated.

It's true the flu vaccination is routinely recommended for people who have a chronic illness. But everyone can benefit from being vaccinated. The influenza virus changes so getting vaccinated each year ensures you have immunity to the strains most likely to cause an outbreak.

• Getting the flu vaccination is all you need to do to protect yourself from the flu.

Also avoid contact with people who have the flu, wash your hands frequently and avoid touching your eyes, nose and mouth with unclean hands.

• You can't spread the flu if you're feeling well.

Twenty per cent to 30 per cent of people carrying the influenza virus have no symptoms.

• You can catch the flu from going out in cold weather without a coat, with wet hair or by sitting near a drafty window.

The only way to catch the flu is by being exposed to the influenza virus. Flu season coincides with the cold weather so people often associate the flu with a cold, drafty environment.

Harvard Health Publications