 Asthma is a chronic inflammatory disorder of the airways, affecting approximately 10% of children. About half the risk is genetically determined, but the rest we may have some control over. One of the reasons asthma rates may be rising is our rising rates of vitamin D deficiency. Kids just aren't going out to play anymore. A doubling of vitamin D insufficiency levels in recent years such that less than a quarter of U.S. teens hit the mark. Vitamin D is the sunshine vitamin. We make no vitamin D from the light coming from our TV or computer screen, so do kids with lower vitamin D levels in their blood have worse asthma? Apparently so, one more than a dozen observational studies suggesting that vitamin D is protective against asthma exacerbations. So should we start giving kids with asthma vitamin D supplements if they're not going to go outside? Well, correlation doesn't mean causation. For example, maybe severe asthma leads to less vitamin D instead of the other way around. To prove cause and effect, you need to put it to the test. Take kids with asthma randomized to one of two groups, vitamin D or an identical looking sugar pill, and see what happens. The problem is there had never been such clinical trials like that until now. Give asthmatic kids between 500 and 1,000 international units of vitamin D3 a day, cuts asthma exacerbations by more than half, perhaps by decreasing the incidence of respiratory infections by boosting immunity while at the same time diminishing inflammation. If it helps with inflammation, what about inflammatory bowel disease? We'll cover that next.