One carrot has enough beta carotene to make 1480mg of vitamin A, more than the daily 800mg.
Red and green peppers provide twice the vitamin C of oranges. Vitamin C helps maintain a healthy immune system, especially after intense exercise.
Kale, which has more vitamin C than citrus fruit, is also rich in beta carotene and vitamin E. Stir-frying with garlic boosts flavor and health.
Garlic may prevent vampires and boost cold immunity. Researchers examined 146 garlic pill or placebo recipients during three months.
Many people lack selenium, which tuna provides. Several years ago, mice with this trace mineral shortage had worse flu virus infections.
Sardines, another immune-boosting fish, contain selenium, vitamin B12, iron, and vitamin D. They all strengthen infection resistance.
Greens, reds, and oranges boost immunity, but mushrooms provide selenium and B vitamins. You can even purchase vitamin D-enriched mushrooms with 2.5mg per 100g (3.5oz).