Recent research from the UK shows how a little sunshine a day (or a daily dose of vitamin D) can protect you against colds and flu.
An important caveat here is that Vitamin D is not what stops the Flu, Vit D is an essential requirement for your body to function optimally. When the requirements of being healthy are met your immune system is capable of protecting you better.
StructuralChiro: http://goo.gl/lNju1s