This is adapted from the book, Eat Smart, Play Hard, by RW USA Nutrition Editor Liz Applegate.
Vitamin C helps protect your body from oxidative damage caused by exercise and other stresses such as air pollution and secondhand smoke. Vitamin C is also critical for maintaining a strong immune system, which can be taxed by endurance exercise.
In a study done at the University of Cape Town Medical School in South Africa, runners took either 600 milligrams of vitamin C a day (10 times the DV) or a placebo for the 3 weeks before an ultramarathon. After the race, the runners who took vitamin C had fewer upper respiratory tract infections than the runners who took a placebo.
My recommendation: Get most of your vitamin C from food. For example, an orange and a kiwifruit each supply close to 100 percent of the DV. Many other fruits and vegetables, such as strawberries, green peppers, and tomatoes, contain more than 50 percent of the DV per serving. If you take supplements, keep your intake below 2,000 milligrams because anything above that level may increase your risk for kidney stones.