It's a classic case of correlation does not imply causation. As implied in the article, people who are sick, stay indoors. So naturally, when they don't get eno

It's a classic case of correlation does not imply causation. As implied in the article, people who are sick, stay indoors. So naturally, when they don't get enough sun from staying indoors, they also get lower levels of Vitamin D. And so that is the correlation. It doesn't mean that a lack of Vitamin D causes illness, or that taking Vitamin D supplements will magically cure those illnesses.