Vitamin D is also really important for immune health. Especially for knowledge workers, who don't normally get enough sun. Recent studies have found that Vitamin D actually activates your T-cells, so without adequate levels, your immune system will act like a depressed dog during a home-invasion and just lay down.
http://wholehealthsource.blogspot.com/2008/10/vitamin-d-its-... http://www.scientificamerican.com/blog/post.cfm?id=another-r...