Can exercise harm my immune system? if i start exercising more frequently will i get sick more often?

Moderation: Most things don't turn out well when done in extremes and thus moderation is the key. Extreme exercises can indeed impair your immune system as in marathoners who suffer from more colds. However exercising for up to 4 hours a week is good for your health. A recent report found that those around age 30 who exercised more than 5 hours a week was at a higher risk for atrial fibrillation.