According to Lifehacker, new studies show that we aren't getting enough Vitamin D, due to sun block. One scientist said, "We are the first society of cave people," he lamented to me in 2010. "In the development process of creating the skin, nature never dreamed that we'd deliberately avoid the Sun so thoroughly."

Without Vitamin D, we can develop terrible diseases. Tumors can spread quicker. There are even a few that say that it can lead to autism (but I'm not at all convinced). 

Still, I think the main finding of the research – we are Vitamin D deficient – is a serious concern. Go outside and garden for twenty minutes today. If I can't get a bad sunburn in 20 minutes, then you're all fine.