There is no current scientific evidence to support the idea that taking Vitamin supplements or large doses of vitamin C will prevent or reduce the symptoms of colds or flu, however you can take discount Vitamins supplements and immune boosting supplements to ensure that you get enough vitamin C on the days you don't eat enough fruits and vegetables. Intense workouts can cause your immune system to fall below normal making you more prone to flue, so it is vital to boost immune system by taking your daily dose of vitamin supplements.