Feeding your body certain foods may help keep your immune system strong. If you're looking for ways to prevent winter colds and the flu, your first step should be a visit to your local grocery store. Plan your meals to include these powerful immune system boosters.... Citrus fruits Most people turn to vitamin C after they've caught a cold. That’s because it helps build up your immune system. Vitamin C is thought to increase the production of white blood cells. These are key to fighting infections. Because your body doesn't produce or store it, you need daily vitamin C for continued health. Almost all citrus fruits are high in vitamin C. With such a variety to choose from, it's easy to add a squeeze of this vitamin into any meal: grapefruit, orange, tangerine, lemon, lime and clementines are all excellent sources. Oats and barley These grains contain beta-glucan, a type of fibre with antimicrobial and antioxidant capabilities more potent than echinacea, reports a Norwegian study. It boosts immunity, speeds wound healing, and may help antibiotics work better. Red peppers If you think citrus fruits have the most vitamin C of any fruit or vegetable, think again. Gram for gram, red peppers contain twice as much vitamin C as citrus fruits. They’re also a rich source of beta carotene which helps keep your eyes and skin healthy. Broccoli Broccoli is supercharged with vitamins and minerals. Packed with vitamins A, C, and E, as well as many other antioxidants and fibre, broccoli is one of the healthiest vegetables you can put on your table. The key to keeping its power intact is to cook it as little as possible - or better yet, not at all. Garlic This potent onion relative contains the active ingredient allicin, which fights infection and bacteria. British researchers gave 146 people either a placebo or a garlic extract for 12 weeks; the garlic takers were two-thirds less likely to catch a cold. Other studies suggest that garlic lovers who eat more than six cloves a week have a 30% lower rate of colourectal cancer and a 50% lower rate of stomach cancer. Ginger Ginger may help decrease inflammation, which can help reduce a sore throat and other inflammatory illnesses. Ginger may help decrease chronic pain and may possess cholesterol-lowering properties, according to recent research, so add it into your diet wherever you can! Spinach Spinach makes the list not just because it's rich in vitamin C. It's also packed with numerous antioxidants and beta carotene, which may increase the infection-fighting ability of our immune systems. Similar to broccoli, spinach is healthiest when it’s cooked as little as possible so that it retains its nutrients. However, light cooking enhances its vitamin A and allows other nutrients to be released from oxalic acid. Turmeric You may know turmeric as a key ingredient in many curries. But this bright yellow, bitter spice has also been used for years as an anti-inflammatory in treating both osteoarthritis and rheumatoid arthritis. Also, research shows that high concentrations of curcumin, which gives turmeric its distinctive colour, can help decrease exercise-induced muscle damage. Green tea Both green and black teas are packed with flavonoids, a type of antioxidant. People who drank 5 cups a day of black tea for 2 weeks had 10 times more virus-fighting interferon in their blood than others who drank a placebo hot drink, in a Harvard study. Where green tea really excels is in its levels of epigallocatechin gallate, or EGCG, another powerful antioxidant. EGCG has been shown to enhance immune function. The fermentation process black tea goes through destroys a lot of the EGCG. Green tea, on the other hand, is steamed and not fermented, so the EGCG is preserved. Green tea is also a good source of the amino acid L-theanine. L-theanine may aid in the production of germ-fighting compounds in your T-cells. To get up to five times more antioxidants from your tea bags, bob them up and down while you brew. Kiwi Kiwis are naturally full of a ton of essential nutrients, including folate, potassium, vitamin K, and vitamin C. Vitamin C boosts white blood cells to fight infection, while kiwi’s other nutrients keep the rest of your body functioning properly. Chicken soup When you’re sick, chicken soup is more than just a feel-good food with a placebo effect. It helps improve symptoms of a cold and also helps protect you from getting sick in the first place. Poultry, such as chicken and turkey, is high in vitamin B-6. Vitamin B-6 is an important player in many of the chemical reactions that happen in the body. It’s also vital to the formation of new and healthy red blood cells. Stock or broth made by boiling chicken bones contains gelatin, chondroitin, and other nutrients helpful for gut healing and immunity. Sunflower seeds Sunflower seeds are full of nutrients, including phosphorous, magnesium, and vitamin B-6. They’re also incredibly high in vitamin E, with 82 percent of the daily recommended amount in just a quarter-cup serving. Vitamin E is a powerful antioxidant. It’s important in regulating and maintaining immune system function. Other foods with high amounts of vitamin E include avocados and dark leafy greens. Shellfish Shellfish isn’t what jumps to mind for many who are trying to boost their immune system, but some types of shellfish are packed with zinc. Zinc doesn’t get as much attention as many other vitamins and minerals, but our bodies need it so that our immune cells can function as intended. Varieties of shellfish that are high in zinc include crab, clams, lobster and muscles. Selenium, plentiful in shellfish helps white blood cells produce cytokines - proteins that help clear flu viruses out of the body. Yoghurt Probiotics, or the "live active cultures" found in yogurt, are healthy bacteria that keep the gut and intestinal tract free of disease-causing germs. Although they're available in supplement form, a study from the University of Vienna in Austria found that a daily 7-ounce dose of yogurt was just as effective in boosting immunity as popping pills. Sweet potato You may not think of skin as part of your immune system. But this crucial organ, covering an impressive 16 square feet, serves as a first-line fortress against bacteria, viruses, and other undesirables. To stay strong and healthy, your skin needs vitamin A. One of the best ways to get vitamin A into your diet is from foods containing beta-carotene (like sweet potatoes), which your body turns into vitamin A.