One of the best ways to keep your immune system strong and prevent colds and flu might surprise you: Shop your supermarket’s produce aisle.

Experts say a diet rich in fruits and vegetables can help you ward off infections like colds and flu. That’s because these super foods contain immune-boosting antioxidants.

What are antioxidants? They are vitamins, minerals, and other nutrients that protect and repair cells from damage caused by free radicals. Many experts believe this damage plays a part in a number of chronic diseases, including hardening of the arteries (atherosclerosis), cancer, and arthritis. Free radicals can also interfere with your immune system. So fighting off damage with antioxidants helps keep your immune system strong, making you better able to ward off colds, flu, and other infections.

Antioxidants for Immunity: Where to Find Them

Adding more fruit and vegetables of any kind to your diet will improve your health. But some foods are higher in antioxidants than others. The three major antioxidant vitamins are beta-carotene, vitamin C, and vitamin E. You’ll find them in colorful fruits and vegetables – especially those with purple, blue, red, orange, and yellow hues. To get the biggest benefits of antioxidants, eat these foods raw or lightly steamed; don’t overcook or boil.

Beta-carotene and other carotenoids: Apricots, asparagus, beets, broccoli, cantaloupe, carrots, corn, green peppers, kale, mangoes, turnip and collard greens, nectarines, peaches, pink grapefruit, pumpkin, squash, spinach, sweet potato, tangerines, tomatoes, and watermelon.

Vitamin C: Berries, broccoli, Brussels sprouts, cantaloupe, cauliflower, grapefruit, honeydew, kale, kiwi, mangoes, nectarines, orange, papaya, red, green or yellow peppers, snow peas, sweet potato, strawberries, and tomatoes.

Vitamin E: Broccoli, carrots, chard, mustard and turnip greens, mangoes, nuts, papaya, pumpkin, red peppers, spinach, and sunflower seeds.

Other super foods that are rich in antioxidants include:

Prunes
Apples
Raisins
All berries
Plums
Red grapes
Alfalfa sprouts
Onions
Eggplant
Beans
Vitamins aren’t the only antioxidants in food. Other antioxidants that may help boost immunity include

Zinc: Found in oysters, red meat, poultry, beans, nuts, seafood, whole grains, fortified cereals, and dairy products
Selenium: Found in Brazil nuts, tuna, beef, poultry and fortified breads, and other grain products


Antioxidant Super Foods: How Much Do You Need?

For optimal health and immune functioning, you should eat the recommended dietary allowance (RDA) of the antioxidant vitamins and minerals. That’s the amount of a vitamin or nutrient that you need to stay healthy and avoid a deficiency.

Here are the RDAs for some antioxidants: 

Zinc: 11 milligrams for men, 8 milligrams for women. If you are a strict vegetarian, you may require as much as 50% more dietary zinc. That’s because your body absorbs less zinc when you have a diet rich in plant-based foods.

Selenium: 55 micrograms for men or women.

Beta-carotene: There is no RDA for beta-carotene. But the Institute of Medicine says that if you get 3 milligrams to 6 milligrams of beta-carotene daily, your body will have the levels that may lower risk of chronic diseases.

Vitamin C: 90 milligrams for men, 75 milligrams for women. Smokers should get extra vitamin C: 125 milligrams for men and 110 milligrams for women.

Vitamin E: 15 milligrams for men and women.

How Foods Boost Immunity

Can’t you get antioxidants from taking a vitamin or a supplement? Yes, but you may be missing out on other nutrients that could strengthen the immune system. Foods contain many different nutrients that work together to promote health. For example, researchers delving into the mysteries of fruits and vegetables and the complex antioxidants they contain have discovered benefits of:

Quercetin: a plant-based chemical (phytochemical) found in apples, onions, teas, red wines, and other foods. It fights inflammation and may help reduce allergies.
Luteolin: a flavonoid found in abundance in celery and green peppers. It also fights inflammation and one study showed it may help protect against inflammatory brain conditions like Alzheimer’s.
Catechins: a type of flavonoid found in tea. Catechins in tea may help reduce risk of heart disease, cancer, and Alzheimer’s disease.
If you can’t get enough antioxidants in your diet by eating fresh produce, some experts recommend taking a multivitamin that contains minerals, too. But be cautious about taking individual immune system supplements to boost immunity. With antioxidants, as with most anything, moderation is key. Vitamins A and E, for example, are stored in the body and eliminated slowly. Getting too much can be toxic.

(Information from WebMD)