Dear Walter Palmer, American dentist - thanks to the media, you're about to learn a little about what it's like to be hunted. Enjoy.
It seems that Vitamin D has a role to play in helping prevent colds or catching the 'flu. Your skin creates Vitamin D from ultraviolet light in sunlight - the kind you get when you're outdoors (glass windows block UV). My extremely biased conclusion: it looks like this is yet another way that going for a walk in the Great Outdoors is really great for your health. You know what to do, folks. Link