Marc Joseph Nutrition - Blog

Why does the flu usually only appear during the winter months and disappear during the summer? A group of researchers just published a review study that suggests vitamin D deficiency may be responsible.

You can read the abstract of the study here, and an excellent summary article (well-worth reading) discussing the study’s primary findings here.

The researchers note that vitamin D has many important effects on the immune system, including:

• Acting as an immune system modulator — preventing excess inflammation and increasing the ‘oxidative burst’ potential of macrophages, a type of immune system cell
• Stimulating the expression of anti-microbial proteins in immune system cells and in cells lining the respiratory tract

When vitamin D is deficient, as it often is during the winter months, the hypothesis is that the body is less able to develop an appropriate immune response and defend against respiratory infections.

In the summary article linked above, one of the study author’s describes how in the hospital in which he worked a flu epidemic developed in Spring 2005. However, all of the patients in his ward had been taking 2,000 IU vitamin D daily for months, and not one of them developed the flu.

Of course, those observations are not definitive proof. More research is necessary to determine cause and effect.

Yet, the authors make a good case in the paper for how vitamin D may explain observations, such as:

1. Why the flu predictably occurs in the months following the winter solstice, when vitamin D levels are at their lowest,
2. Why it disappears in the months following the summer solstice,
3. Why influenza is more common in the tropics during the rainy season,
4. Why children exposed to sunlight are less likely to get colds,
5. Why cod liver oil (which contains vitamin D) reduces the incidence of viral respiratory infections,
6. Why the elderly who live in countries with high vitamin D consumption, like Norway, are less likely to die in the winter,
7. Why the elderly are so much more likely to die from heart attacks in the winter rather than in the summer,
8. Why African Americans, with their low vitamin D blood levels, are more likely to die from influenza and pneumonia than Whites are.

Bottom-line, it’s important to maintain vitamin D at summer-time levels year-round. For people living in higher latitudes where the intensity of the sun’s UV rays are not strong enough to generate vitamin D during the winter, the only way to do that is with sun lamp exposure or supplementation. If using supplementation, it’s also important to monitor your vitamin D levels to ensure that you don’t get too much.

This entry was posted on Monday, November 13th, 2006 at 10:07 pm and is filed under Viral Infections, Vitamins. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.