ive found that the best thing to blast away at a cold are garlic tablets, sure they're unscented when you take them, but once they're in your stomach and have worn away the coating on the tablet, and you burp, well yeh
but they are really good for sinus infection, blocked noses and headcolds in general, take AT MAX 3 a day, else youll b in for a bit of bowel upset.
I also found that another useful thing to keeps colds at bay is halibut liver oil. contains omega 3s and stuff.

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Sleep is the best thing. Also be sure to include high intensity training in the mix when doing long duration. If you only do moderate to lower intensity you wind up lowering HGH and testosterone levels and mess up your recovery and lower your metabolic rate too.