Hydrate with tons of water throughout the day, and your immune system will thank you. The foods you eat can also help prevent the cold. Yogurt, with all its probiotic glory, has been shown to boost the immune system, and one serving of seaweed packs more vitamin C than an orange. Another immunity booster? An autumn favorite: Pumpkins. They’re high in beta carotene, which your body converts into vitamin A. In turn, vitamin A helps strengthen your immune system.