A well-functioning immune system is key to fending off foreign invaders, pathogens, and infections. While many factors can compromise the body’s defense network, nutrition plays a key role in supporting the immune system. Here we navigate the nutrients critical to ensure a competent, robust immune system. Plus, you’ll walk away with more than a grocery cart full of immune system boosting foods!
Zinc. Perhaps the best recognized “immuno-nutrient” is zinc. It’s involved in hundreds of metabolic processes, including the body’s immune responses. A clear example of zinc’s importance is the severely depressed immune function associated with its deficiency.1 The best dietary sources of zinc are pumpkin seeds, sesame seeds, seafood (e.g., oysters, scallops, shrimp), beef, spinach, and cashews.
Selenium. Like zinc, selenium is a critical player in many of the body’s processes. It’s particularly well-known for its antioxidant defenses,2 which enhance immune function. Brazil nuts are one of the most highly regarded sources of selenium. But it’s also found in eggs, beef, sardines, and seafood (e.g., scallops, shrimp).
Vitamin A. Vitamin A and its metabolites (such as β-carotene) play an important role in the immune system. This vitamin improves gut barrier function, enhances immune responses, reinforces mucus secretion, enhances natural killer cell activity, and reduces susceptibility to infection.2 Orange-colored fruits and vegetables (such as carrots, pumpkin, sweet potatoes, mangos, papaya, and cantaloupe) are excellent immune system boosting foods, because of the β-carotene. And dark leafy greens, bok choy, bell peppers, and broccoli are also good sources.
B vitamins. Certain B vitamins—notably B6, folate, and B12—help ensure a properly functioning immune system. Inadequate intake of any of these may impair immunity and increase susceptibility to infection. The richest sources of B6 are wild salmon, tuna, turkey, chicken, beef, potatoes, sunflower seeds, spinach, and bananas. Meanwhile, your best bets for folate are lentils, beans, asparagus, and dark leafy greens. The best foods for B12 are sardines, wild salmon, lamb, scallops, shrimp, beef, and dairy.
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Vitamin C. Ask anyone about immune system boosting foods, and vitamin C is probably the first nutrient that comes to mind. Indeed, certain cells of the immune system need vitamin C to perform their functions. And a deficiency in vitamin C results in a reduced resistance to pathogens. However, there’s no need to go overboard, as super-doses of vitamin C are unlikely to prevent the common cold or reduce its severity.3 Having said that, vitamin C can enhance the immune system. So, make sure you’re eating plenty of citrus fruits (e.g., oranges, grapefruit, clementine, and tangerines), bell peppers, bok choy, broccoli, Brussels sprouts, strawberries, pineapple, kiwifruit, cauliflower, dark leafy greens, cabbage, and tomatoes, which are all good sources of vitamin C.
Vitamin D. The traditional view is that vitamin D, often referred to as the “sunshine vitamin,” plays an important role in building and maintaining healthy bones. But now we know it does much, much more. This is because the human body is laced with vitamin D receptors throughout, including the cells of the immune system.
Vitamin D influences both the innate and adaptive immune responses.4 While sun exposure is the best way to increase levels of vitamin D, it can also be found in oily fish (e.g., wild salmon, sardines, mackerel), egg yolks, and mushrooms.
Vitamin E. As the major fat-soluble antioxidant in the body, vitamin E protects the fat-based walls of our cells from free-radical damage (called lipid peroxidation). This damage suppresses the immune system. So, it’s crucial to maintain, if not enhance, the body’s immune response.2 Dark green leafy vegetables (like spinach, kale, mustard greens, collard greens, turnip greens, and Swiss chard), sunflower seeds, asparagus, almonds, broccoli, bell peppers, and tomatoes are all very good sources of vitamin E and are top immune system boosting foods.
Copper. The immune system requires copper for several functions. When there’s not enough copper around, activity of some of the key players (e.g., interleukins, T-cells) in the body’s immune response are suppressed.5 You can get your copper fix by eating Brazil nuts, sesame seeds, pumpkin seeds, spinach, shrimp, and cashews.
Iron. When it comes to immunity, iron can be a double-edged sword. That’s because it’s a required nutrient for both humans and pathogens. In fact, the immune system can keep bugs at bay by depriving them of iron. So, while iron stimulates immunity, it’s important to be cautious not to overdo it. Overdoing it may actually increase susceptibility to infection.
Beef is the best source of dietary iron as it is a much more readily absorbed form (i.e., heme). However, iron can also be obtained from plant-based foods (i.e., non-heme), such as sesame seeds, pumpkin seeds, and spinach.
Probiotics. Fermented foods such as yogurt, kefir, sauerkraut, pickles, kimchi, kombucha, miso, tempeh, natto, and wine are the best sources of probiotics. These fermented foods are most commonly regarded for supporting a healthy balance of gut bacteria and aiding in digestion and absorption. One of the more commonly recognized, yet overlooked benefits of probiotics is that they may help support a healthy immune system. It’s estimated that the digestive system contains over 70% of your immunity.6 So, probiotics are considered premium immune system boosting foods by helping support a healthy inflammatory response, enhancing intestinal barrier function, and more.7
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Prebiotics. Certain types of fiber (such as oligosaccharides, β-glucans, gums, some hemicelluloses, and resistant starches) serve as “food” for the good bacteria in the large intestine. Prebiotics support immunity by promoting a healthy balance of gut microbes.8 When prebiotic fibers are fermented by bacteria, it leads to the production of short-chain fatty acids (SFCA). These serve as fuel for the immune system (among a variety of other health properties).6,9,10 Prebiotics occur naturally in foods such as leeks, asparagus, chicory, Jerusalem artichokes, garlic, onions, whole grains (e.g., oats, wheat, corn), and soybeans.11
Resistant starch can be found in green unripe bananas, uncooked oats, and cooked-then-cooled potatoes, rice, beans, and lentils.
β-glucan. β-glucan is not only a prebiotic fiber, it also enhances the function of two of the most important players in the body’s immune responses: macrophages and natural killer (NK) cells.12 The best-known dietary source of β-glucan is oats. Oats are highly regarded for their ability to lower both total and LDL (“bad”) cholesterol levels—effects attributed to, you guessed it, β-glucan. In addition to oats, other cereal grains (e.g., barley), certain types of mushrooms (e.g., reishi, shiitake), and seaweed are considered immune system boosting foods, due to their level of β-glucan.
Glutathione. A healthy and properly functioning immune system relies heavily on having optimal levels of glutathione, which is frequently referred to as the body’s “master antioxidant.”13 Glutathione supports immunity by replenishing the body’s primary defense system. It is also a natural detoxifier, helping to eliminate potentially harmful toxins.
Research suggests that dairy-based foods (e.g., milk, cheese, yogurt) are most effective at raising levels of glutathione in the body.14 Whey protein is arguably most effective at boosting levels of glutathione. Whey is rich in the amino acid cysteine, which is necessary for the body to synthesize glutathione. 15 Speaking of whey, it’s also rich in the amino acid glutamine. This amino acid is also required for optimal immune system function. In addition, whey protein contains immunoglobulins and lactoferrin. These are established immune-enhancing nutrients.16 If possible, choose a whey protein supplement that comes from grass-fed cows, which contain higher concentrations of glutathione.17
That’s a lot of immune system boosting foods! The point isn’t that you need to eat ALL of them EVERY day. Rather, eat a variety of these whole, nutrient-dense foods regularly. If you can adopt this pattern of eating, you are more likely to have a robust, well-functioning immune system to show for it!