Need another reason to exercise? Do it to boost your immunity this winter! But, beware -- exercising too much can actually have the opposite effect.

Exercising too much and too intensely can cause upper respiratory infections -- which makes me wonder if all my years of playing basketball and volleyball had anything to do with my yearly bout with bronchitis, which tapered off when I entered college.

Basically, you want to exercise enough to maintain a healthy weight, which will in itself help you battle colds and flu, and you'll sleep better. Body + Soul magazine also recommends managing your stress as much as possible by eating well, getting some probiotics, taking the right supplements (like astragalus) and making sleep a priority.