I also enjoyed that article. There is a lot of talk about vitamin D lately. I heard an interesting piece on the Diane Rhem show on NPR last July.
Some of the answers of one of the guests to questions by callers bothered me a bit. He seemed to downplay the role of vitamin D from sunlight in favor of obtaining it from supplements. It turns out he's got somewhat of a vested interest in supplements: he's the Director of the Office of Dietary Supplements at the National Institutes of Health.
I found an excellent article on recent (2006) research at the following URL:
Basically it summarizes a study published in Epidemiology and Infection
(2006), 134: 1129-1140, in which the author traces the season oubreaks of infuenza, especially in the northern hemisphere and the rainy season in the tropics and suggests that it has something to do with our lack of exposure to the sun. Ultraviolet radiation helps reduce the incidence of viral respiratory infections. Other theories such as "crowding" in the winter months don't make much sense, since our modern culture tends to crowd year round, especially in the workplace, and we do not see high influenza levels in the summer.
The abstract of the study discussed can be found here:
The best source of vitamin D by far is sun exposure. We should all make an effort to continue to get as much sun exposure as possible during the winter months. I think there is more to it than the vitamin D our bodies manufacture when we are in the sun. Sun exposure seems to trigger a whole series of chemical reactions that are advantageous to our health. The vitamin D we get from fortified foods (i.e. cows milk, soy milk) is a paltry amount compared to what we get from 15 minutes in the sun. Nevertheless, if we are not getting enough sun, supplementation is better than getting no vitamin D at all.