nothing pounds your immune system in the dirt more than stress and lack of sleep (which is a stresser)
check out my fasting Ebook, link in my signature. fasting is a great way to help your body rest as 50% of your bodies energy goes to digesting foods. so if you fast your body will benefit a lot.. plus it also re-cycles your WBC's
Yes, you need to take care of health during winter. I think the idea of vitamins is quite a good one. You just have to make sure that the vitamins that you decide to take will promote maximum fat burning and also safeguard your prostate and urinary health.