The single best way to ward off a cold is to keep your immune system healthy, and adequate rest is the cornerstone to keeping your natural defense mechanisms humming at peak efficiency. A published review from a sleep laboratory in Belgium in 2011 showed increased systemic inflammation and decreased white cell function, both markers of an altered immune system, in people with chronic sleep reduction. Strive for a minimum of eight hours of sleep a night and increase to nine or 10 hours if you feel a cold is coming on. It could be just the thing to lessen a cold's duration or ward it off entirely.