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As we head into the season of respiratory viruses, it’s a good idea to take proactive steps to bolster your immune system.
And that includes eating a diet plentiful in immune-supportive foods.
While no single food – or nutrient for that matter – can enhance your immune system, an overall healthy diet is vital for a robust immune defense.
Whole foods deliver a wide variety of immune-enhancing nutrients. Add them to your regular diet this fall and winter.
The diet-immunity connection
The immune system is a complex network of cells and tissues that relies on a steady influx of nutrients to fight off infection.
Key nutrients support the immune system by maintaining a strong intestinal barrier, building white blood cells and antibodies, and fueling the growth and activity of immune cells.
Dietary antioxidants and many phytochemicals also protect immune cells from damage caused by oxidative stress and inflammation.
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This list of foods isn’t exhaustive but it serves as a good starting place to build an immune-friendly diet. Include other foods with similar nutrients in your diet, too.
Yellow bell peppers
These peppers are an exceptional source of vitamin C, an antioxidant that shields immune cells from damaging free radicals. (Free radicals are unstable oxygen molecules that are generated during the body’s immune response.)
Vitamin C also enhances the ability of immune cells called phagocytes to engulf and destroy pathogens.
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The official recommended daily allowance, or RDA, for vitamin C is 90 mg for men and 75 mg for women. Some experts, however, advise consuming 200 to 400 mg daily for optimum health.
Half of a large yellow bell pepper packs in an impressive 170 mg of vitamin C.
Other good sources of vitamin C include red and green bell peppers, broccoli, cauliflower, Brussel sprouts, kiwifruit, strawberries, citrus fruit and pineapple.
Salmon
This oily fish is a multitasker when it comes to supporting immune health.
It’s one of few foods that naturally contains vitamin D, a nutrient that stimulates immune cells to produce antimicrobial proteins, dampens inflammation and increases the activity of phagocytes.
Vitamin D also strengthens the protective barrier of epithelial cells, which make up the body’s first line of defence. Doing so makes these physical barriers more resistant to viruses.
Plus, fatty fish such as salmon are excellent sources of omega-3 fatty acids, which help various immune cells work properly. These fats also protect immune cells by reducing inflammation.
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And fish is an excellent source of the mineral selenium, a vital component of two key antioxidant enzymes in the body that reduce oxidative stress.
The RDA for vitamin D, which is based on bone health, is 600 international units, or IU, for people ages 1 to 70 and 800 IU for older adults.
Per three ounces, you’ll find 715 IU of vitamin D in canned sockeye salmon, 479 IU in canned pink salmon and 447 IU in cooked Atlantic salmon.
Frozen spinach
This leafy green is an excellent source of vitamin E, an antioxidant that protects immune cell membranes from free radical damage.
The nutrient also enhances the activity of T cells, white blood cells crucial for fighting infection.
One half-cup of frozen spinach delivers 3.4 mg of vitamin E, nearly one-quarter of your daily requirement (15 mg).
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What’s more, cooked spinach is an outstanding source of beta-carotene, which the body converts to vitamin A, a critical nutrient for immune function.
Sunflower seeds, almonds, hazelnuts, peanuts, cooked Swiss chard, sunflower oil, safflower oil and grapeseed oil are also rich in vitamin E.
Kefir
This fermented milk product is source of prebiotics, non-digestible carbohydrates that indirectly enhance the immune system.
Prebiotics feed beneficial gut bacteria, which, in turn, produce short chain fatty acids. These compounds stimulate the activity of gut immune cells (70 per cent of the immune system is located in our gut).
Short chain fatty acids also play a role in strengthening the intestinal barrier and decreasing inflammation.
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Kefir, like many other fermented foods (e.g., yogurt, kombucha, kimchi, unpasteurized sauerkraut) also contains a mix of probiotics and, as such, can help increase the population of beneficial gut microbes.
Other prebiotics include asparagus, Jerusalem artichokes, jicama, leeks, onions, garlic, apples, bananas, whole grain rye, barley, white kidney beans, chickpeas, soybeans and chicory root.
Lentils
This small pulse is an exceptional source of folate, a B vitamin that’s essential for forming new immune cells. It’s used to make DNA, RNA and proteins needed for rapidly dividing immune cells.
Folate is also thought to have anti-inflammatory effects in the immune system.
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One cup of cooked lentils delivers a hefty 358 mcg of folate; adults require 400 mcg each day.
Lentils also are a good source of zinc, needed for the proper development and function of immune cells
Other folate-rich foods are cooked spinach, black beans, kidney beans, asparagus, broccoli, Brussels sprouts, green peas and avocado.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on X @LeslieBeckRD