During my trip to Florida a couple weeks ago, I seemed to have picked up a "bug" of sorts, perhaps from the airplane flight. Unlike my recent experiences, I wasn't able shake it off quickly.
The last couple of years in Las Vegas, before moving to Buffalo, I didn't really get sick. A few times I felt a bug coming on, but then I would fast for a day and that would knock it out. I tried that with this most recent cold, but it didn't seem to work. The cold kept lingering on.
This last week I put a ton of energy into researching colds. My first thought was, why did I not get sick in Las Vegas but did get sick in Buffalo? Obviously, there's a big temperature difference, but my research led me to what I think is the most important factor: sunlight.
Last year, a major paper was published that linked the lack of Vitamin D to the flu. Vitamin D is naturally produced by the body when it is exposed to sunlight. But in the winter and especially in northern latitudes, the body isn't exposed to sufficient sunlight. However, a person can get Vitamin D though other sources, such as seafood or over-the-counter supplements.
For decades, researchers knew that colds were more prevalent in the winter than the summer, but no one was exactly sure why. One of the authors of the paper, John Cannell, believed that this was simply due to the lack of sunlight. In fact, his theory about sunlight/Vitamin D and influenza would explain the following known observations:
- Why the flu predictably occurs in the months following the winter solstice, when vitamin D levels are at their lowest
- Why it disappears in the months following the summer solstice
- Why influenza is more common in the tropics during the rainy season
- Why the cold and rainy weather associated with El Nino Southern Oscillation (ENSO), which drives people indoors and lowers vitamin D blood levels, is associated with influenza
- Why the incidence of influenza is inversely correlated with outdoor temperatures
- Why children exposed to sunlight are less likely to get colds
- Why cod liver oil (which contains vitamin D) reduces the incidence of viral respiratory infections
- Why Russian scientists found that vitamin D-producing UVB lamps reduced colds and flu in schoolchildren and factory workers
- Why Russian scientists found that volunteers, deliberately infected with a weakened flu virus - first in the summer and then again in the winter - show significantly different clinical courses in the different seasons
- Why the elderly who live in countries with high vitamin D consumption, like Norway, are less likely to die in the winter
- Why children with vitamin D deficiency and rickets suffer from frequent respiratory infections
- Why an observant physician (Rehman), who gave high doses of vitamin D to children who were constantly sick from colds and the flu, found the treated children were suddenly free from infection
- Why the elderly are so much more likely to die from heart attacks in the winter rather than in the summer
- Why African Americans, with their low vitamin D blood levels, are more likely to die from influenza and pneumonia than Whites are
This association between Vitamin D and the flu is still just a theory at this point, though it does fit in nicely with evolutionary theory as well. Humans evolved near the tropics and spent consideable parts fo the day out in the sunlight, suggesting that moderate exposure to sunlight is a part of our evolutionary past.
As to empirical evidence, here's a post about my own (successful) self-experimentation with Vitamin D. And for more great information, go the website for the Vitamin D Council.