Check Your Vitamin D
Higher blood levels of vitamin D are associated with fewer infections of the respiratory tract, according to one large observational study. Since vitamin D deficiency is so common, it's worth talking to your doctor about getting your levels checked. If you're deficient, your doctor can recommend an appropriate daily or weekly supplement. If you don't have a vitamin D deficiency, however, further supplementation to reach higher-than-normal blood levels isn't likely to be beneficial.