Now that the world is convinced that the swine flu apocalypse is nigh and the season of snottynosed brats at daycare is upon us, I’d like to draw your attention to a very easy, yet important, public health and prevention measure.

Vitamin D.

Recent research, confirmed by the World Health Organization, indicates that an enormous number of people are deficient in vitamin D. One study from U of Calgary suggests that up to 97% (!!) of Canadians are deficient at least occasionally.

As you know we manufacture D from sunlight. However our bodies evolved to be naked in Africa, not clothed under fluorescent lights. There is almost NO source of D naturally occurring in food.

And yet Vitamin D plays a crucial role in our body’s metabolism, almost more so than nearly any other vitamin. For example it helps regulate our calcium metabolism and thus bone health. It lowers cancer and cardiovascular disease risk. Indeed, a study using US national health data showed that vitamin D independently predicted risk of premature death from all cause mortality — in other words, low vitamin D = more risk of dying early from chronic disease.

In particular, D is involved in regulating and boosting our natural immunity.

A preponderance of evidence shows that D deficiencies create depressed immune systems, which leaves you vulnerable to micro-organisms. This is one key reason that incidence of colds/flus etc increases in winter. (Or you can take my word for it. Trust me: I’m a doctor.)

How much to take? To achieve a “summertime sunlight” blood concentration of about 50 ng (that’s nanograms) per mL of blood, studies have found that somewhere between 3000 to 5000 IU daily is needed.

The average person can probably benefit from around 2000 IU in the winter. The author of the study listed below notes that “studies indicate that ideal daily doses of vitamin D exceed current recommendations by an order of magnitude.”

In other words, current recommendations are WAY too low.

People with darker skin are more at risk, as are people living farther north — e.g. people of African or South Asian descent, many First Nations people in Canada (esp. those not eating a traditional diet). Also at risk of major deficiency are children, adolescents, and older people. Um, so basically everyone.

But isn’t D toxic?

Well, “administration of 4000 IU/day of vitamin D for more than 6 months to middle-age Canadian endocrinology outpatients, resulted in average 25(OH)D levels of 44 ng/ml [close to what we want] and produced no side-effects other than an improved mood.” (Cannell 2006)

In other words, not as much as we’ve been led to believe.

Vitamin D is cheap and easily available. Buy the D3 aka cholecalciferol, the animal-derived format, rather than D2, which is relatively poorly converted.

My recommendation is to take *at least* 1000 IU a day starting right now. As the weather gets colder and we move inside, bump the dose to at least 2000 IU. Take it with food, in divided doses if you like. Just take it.

And say sayonara to swine.

Cannell, JJ et al. Review Article: Epidemic influenza and vitamin D. Epidemiol. Infect. (2006), 134, 1129–1140. doi:10.1017/S0950268806007175