Vitamin D

Though your body makes vitamin D when the the sun hits your skin, if youre cooped up inside sick or in a cold climate youre likely not getting enough of this important nutrient. Many foods are now fortified with vitamin D, the most notable being most milk products. (Bonus fact: contrary to popular belief, drinking or eating dairy does not increase your bodys mucus production! So have a glass of cow juice and, at the same time, lower your chances of getting a respiratory infection.)