Nutrition • 13 Apr 2020

Nutrition for Immune Health

By uci_admin

By Karen Lindsay, PhD, RDN.

Now, more than ever, is the ideal time to invest in improving our nutrition. Not only are the majority of us spending more time at home, with opportunities to cook and explore new recipes, but good nutrition is critical to strengthen the immune system and reduce our chances of viral infections. Afterall, our immune system comprises numerous proteins and requires vitamins, minerals and a whole host of other nutritional compounds to coordinate up-regulation and attack of foreign bodies, such as viruses, that we may encounter.1

The fundamental elements of a good diet for immune health include:

  1. Abundant vegetables and fruit: Aim to eat a wide variety that includes all colors of the rainbow, which is indicative of the different nutrients and phytonutrients they contain. Fresh and frozen vegetables are best in terms of nutritional quality. Try to include some vegetables at every meal to help meet your micronutrient goals. This can take the form of salad, homemade soup, juices and smoothies, or cooked as part of a main dish. We are fortunate here in Southern California that fresh produce is abundantly available during this time when pantry goods may be in lower stock. Several smaller farmer’s markets remain open too, which is a great opportunity to purchase fresh, seasonal produce outside of grocery stores, while also supporting your local farmers!
  2. High quality protein: Amino acids, the building blocks of all proteins, are essential to create many elements of the immune system and maintain its optimal functioning. The best animal protein sources include bone broth, grass-fed or pasture-raised meats, fish and seafood, pasture-raised eggs. Plant protein sources include beans and legumes, nuts and seeds, and soybean based products such as tofu and tempeh. An added benefit of most protein-rich foods is that they also contain the immune-boosting mineral zinc. Consuming approximately two 4 ounces servings of protein rich-foods foods per day will support immune functioning.
  3. Reduce or eliminate simple sugars and highly processed foods: During times of uncertainty, anxiety, fear or boredom, we often reach for the high sugar, processed snacks (e.g. candy, cookies, chips) and low-fiber starchy foods (e.g. white bread, pasta). Not only do these foods provide little to no nutritional value, but the elevated blood sugar response after eating them actually suppresses the immune system and makes us more vulnerable to infections. Furthermore, if we do get sick, raised blood sugar levels from frequently consuming these foods could prolong and increase the severity of an infection.2
  4. Probiotic and prebiotic foods: The gut microbiota is a very important part of our immune system as healthy bacteria and other microbes in our gut help to recognize and fight off harmful infectious agents, such as viruses. We can support a healthy gut microbiome by eating fiber-rich foods such as vegetables, fruits, nuts, seeds, beans and legumes, and by avoiding simple sugars and processed foods as mentioned above.

Particularly beneficial fruits and vegetables that help feed the good bacteria in our guts (i.e. prebiotics) include:

  • Artichokes
  • Asparagus
  • Apples
  • Banana
  • Dandelion greens
  • Flaxseed
  • Jicama
  • Onion family e.g. white/red/green onion, leeks, garlic

Additionally, fermented foods are excellent natural sources of healthy probiotic bacteria to incorporate in your diet. Try supplementing your meals each day with fermented foods such as:

  • Kefir
  • Kimchi
  • Pickles
  • Sauerkraut
  • Yogurt

Other key foods and nutrients to support the immune system include:

  • Herbs and spices; many have potent anti-inflammatory and immune-boosting properties such as ginger, turmeric, garlic, oregano, rosemary and chilli pepper.
  • Flavanoids are chemicals naturally found in a range of plant foods and tea (especially green tea) that have anti-viral properties. Quercetin appears to be a particularly beneficial flavonoid for helping to fight influenza viruses.3 Onions, capers, dill, oregano and broccoli are excellent sources.
  • Vitamin C has long been recognized as an essential vitamin to support immunity, particularly for viruses of the upper respiratory system.4 The richest dietary sources include citrus fruit, rosehip, strawberries, green leafy vegetables, broccoli, potatoes.
  • Vitamin D helps to modulate the immune system and to produce antimicrobial proteins in the case of an infection.5, 6 The best source is natural sunlight exposure on bare skin for short bursts each day. Some vitamin D containing foods include beef liver, egg yolk, fatty fish (e.g. salmon, mackerel, sardines), fortified milk or milk alternatives, and mushrooms.
  • Vitamin A supports the development of immune cells, antibody responses to infections and maintains the mucosal lining of our lungs.7 Rich dietary sources include fish, liver, egg yolks and orange colored vegetables.
  • Zinc plays a critical role in supporting the structure and function of our immune system.8 The best dietary sources include grass-fed beef and lamb, shellfish, beans, legumes, nuts and seeds, milk and milk products.
  • N-acetyl-cysteine (NAC) is a powerful amino acid antioxidant and may be particularly supportive for lung health and treating pneumonia.9 While consuming protein-rich foods will provide a source of NAC, it can also be taken as a supplement (e.g. 600mg/day).
  • Black elderberry has been shown to reduce the severity of upper respiratory symptoms from cold and flu viruses.10 It may be taken in capsule form or as a raw syrup.

In summary, “let food be thy medicine” and nourish your body at this critical time when health is a concern for all.


  1. Childs CE, Calder PC, Miles EA. Diet and Immune Function. Nutrients. 2019;11(8):1933.
  2. Hulme KD, Gallo LA, Short KR. Influenza Virus and Glycemic Variability in Diabetes: A Killer Combination? Front Microbiol. 2017;8:861-.
  3. Wu W, Li R, Li X, He J, Jiang S, Liu S, Yang J. Quercetin as an Antiviral Agent Inhibits Influenza A Virus (IAV) Entry. Viruses. 2015;8(1):6.
  4. Hemila H, Louhiala P. Vitamin C for preventing and treating pneumonia. Cochrane Database Syst Rev. 2007(1):Cd005532.
  5. Baeke F, Takiishi T, Korf H, Gysemans C, Mathieu C. Vitamin D: modulator of the immune system. Curr Opin Pharmacol. 2010;10(4):482-96.
  6. Wang TT, Nestel FP, Bourdeau V, Nagai Y, Wang Q, Liao J, Tavera-Mendoza L, Lin R, Hanrahan JW, Mader S, White JH. Cutting edge: 1,25-dihydroxyvitamin D3 is a direct inducer of antimicrobial peptide gene expression. J Immunol. 2004;173(5):2909-12.
  7. Stephensen CB. Vitamin A, infection, and immune function. Annu Rev Nutr. 2001;21:167-92.
  8. Wessels I, Maywald M, Rink L. Zinc as a Gatekeeper of Immune Function. Nutrients. 2017;9(12):1286.
  9. Zhang Q, Ju Y, Ma Y, Wang T. N-acetylcysteine improves oxidative stress and inflammatory response in patients with community acquired pneumonia: A randomized controlled trial. Medicine (Baltimore). 2018;97(45):e13087-e.
  10. Hawkins J, Baker C, Cherry L, Dunne E. Black elderberry (Sambucus nigra) supplementation effectively treats upper respiratory symptoms: A meta-analysis of randomized, controlled clinical trials. Complement Ther Med. 2019;42:361-5.
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