Taking vitamin C before engaging in physically demanding activities helps keep colds away for people that are heavy exercisers, say Finnish researchers at the University of Helsinki. While their meta-study showed that non-exercisers that took vitamin C daily gained little or no protection from colds, the story for marathoners, competitive skiers and soldiers on subarctic assignments was much different. The study, published in the Cochrane Review, found that the 598 heavy exercisers cut their risk of colds in half.