Nutrition is a critical component to improving immune function, especially during the COVID-19 pandemic. Consuming essential nutrients can help you avoid this infectious disease.
Here are some of the most important nutrients for immune function and how they work.1
Vitamin A: is associated with healthy epithelial tissue, improved barrier function, and immune cell maturation. A deficiency diminishes natural killer cell activity and, as a result, impairs antiviral defenses. It also predisposes the person to higher risk of respiratory infections and diarrhea. Good food sources of vitamin A include milk, eggs, liver, dark orange fruits and vegetables, and tomato juice.
B Vitamins: also contribute to intestinal immune regulation and gut barrier function. B6, B12, and folate support the activity of the natural killer cells and CD8 cytotoxic T lymphocytes, which are important in defense against viruses. A deficiency of vitamin B12 decreases phagocytic and bacterial killing ability of neutrophils. B-vitamin food sources includes fish, meat, whole grains, fortified cereals, and green leafy vegetables.
Vitamin C: studies have found that it shortens the duration of the common cold and decreases the severity and mortality from pneumonia. Vitamin C also helps leucocytes move to sites of infection, increases antibody production, and improves T lymphocyte function. Vitamin C is highest in citrus fruits, red and green peppers, strawberries, and broccoli.
Vitamin D: receptors are in most immune cells and some cells of the immune system can even synthesize the active form of vitamin D from its precursor. Vitamin D enhances epithelial integrity and stimulates antimicrobial peptide synthesis in epithelial cells and macrophages, which enhances defenses. A small JAMA Network Open study found people with vitamin D deficiency was associated with a 77 percent increased risk of being infected with COVID-19.2 Vitamin D can be produced from UV exposure of even 10-15 minutes, but it’s also in fortified milk, oily fish, and eggs.
Vitamin E: improves T helper 1 cell-mediated immune response, enhances antibody production, neutrophil chemotaxis, and phagocytosis. Along with being an antioxidant, vitamin E improves vaccination response, and deficiencies are known to increase the susceptibility of a person to infectious disease. Good food sources of vitamin E are nuts and seeds, many vegetable oils, and wheat germ.
Zinc: inhibits the RNA polymerase required by RNA viruses, like coronaviruses, to replicate, suggesting it may play a key role in host defense.1 Zinc is important in maintaining T and B lymphocyte numbers and antibody production. Studies of supplementation for zinc deficiencies report shorter duration of colds and reduced mortality in adults with pneumonia.3 Good food sources of zinc include shellfish, meat, and cheese.
Copper: has antimicrobial properties and supports neutrophil, monocyte and macrophage functions, and natural killer cells. Copper promotes T lymphocyte responses, including Interleukin-2 production.4 A deficiency leaves people open to impaired immune responses. Food sources of copper include sesame seeds, cashews, soybeans, lima beans, and lentils.
Selenium: supports T and B lymphocyte function including antibody production. Deficiencies have been associated with lower killer cell activity and increased mycobacterial disease. Selenium deficiency has been shown to permit mutations of coxsackievirus, polio virus, and murine influenza virus increasing their virulence.5 Supplementation has been used in the UK on people with low selenium status to improve immune response to the poliovirus vaccine.6 Foods with higher amounts of selenium include Brazil nuts (not to exceed 2 nuts per day), fish, shellfish, meat, and eggs.
Iron: stores that are adequate improve resistance to infection. Paradoxically, iron supplementation is not recommended in malaria areas and tropics where it appears to cause impairment of immune function above a certain threshold. Explanations range from causing increased inflammation to some pathogens use iron to grow. Iron is found naturally in meat, liver, beans, nuts, dried fruits, brown rice, fortified cereals, spinach, and kale.
And although it’s not exactly a nutrient, gut microbiota is credited with being responsible for a high percent of immune function through an active barrier to pathogens. The gut microbiota shows high variability between individuals, usually due to their environment, habitual food choices, age, chronic disease, ethnicity, and medications. A diet higher in fermented foods, cultured dairy, fruits and vegetables, and fiber keep the microbiome fed and healthier.
So those are just some of the most important nutrients that can help keep our immune system strong.
Dietary Recommendations for the COVID-19 Pandemic
Now that we know what some of the most important nutrients are, what do we suggest eating during the COVID pandemic? Here are a few recommendations for improved nutritional heath.
Eat two cups of well washed, colorful fresh fruits, including berries, bananas, apples, oranges, grapes, tomatoes, and any other wonderful fruits from local farmers, food banks, or grocery stores. A one-half cup portion counts as one serving and one medium banana counts as one cup! (And yes, tomatoes are classified a fruit.) If fresh fruits and vegetables are not available, then eat frozen or canned.
Along with fruit, a person should eat at least three one-half cup servings of vegetables per day, especially leafy greens, carrots, sweet potatoes, mushrooms, onions, garlic, and cruciferous vegetables like broccoli, kale, and brussels sprouts, as well as green beans, corn, celery, and white potatoes.
We also suggest eating whole grains, nuts, lean meats and poultry, fatty fish, shellfish, organ meats, milk, cheese, olive oil, fortified cereals, and drinking plenty of clean water.
To reduce inflammation, we suggest avoiding sugars, fried foods, and foods with trans fats and hydrogenated oils while we recommend eating more foods high in omega-3 fats, which are in cold water fish, ground flax seed or flax oil, leafy green vegetables, and walnuts.
We also suggest foods high in antioxidants like yellow, red, and orange vegetables—so that’s peppers and carrots, dark leafy greens, citrus fruits, black and green teas, and allium vegetables like onions and garlic. Other foods that reduce inflammation are high in fiber, which come from fruits, vegetables and whole grains, and spices like ginger, turmeric, rosemary, oregano, and nutmeg.
Through this pandemic time, we also suggest taking a good quality multi-vitamin and mineral supplement.
So just to bring all of this together, is nutrition intertwined with the incidence and severity of catching COVID-19 and suffering its consequences? No doubt about it! Of course there are many other contributing factors, but the quality and quantity of nutrient intake, along with exercise to push and pull nutrients and toxins in and out of cells, plus adequate clean water and air are what maintain a person’s life and health from birth.
Every bite of food interacts with body systems. That is why food choices are so important.
- Calder PC. Nutrition, immunity, and COVID-19. Accessed 11/10/2020. https://nutrition.bmj.com/content/early/2020/05/20/bmjnph-2020-000085
- Dunleavy BP. Vitamin D deficiency raises COVID-19 infection risk by 77%, study finds. UPI. Accessed 9/8/2020. https://www.upi.com/Health_News/2020/09/03/Vitamin-D-deficiency-raises-COVID-19-infection-risk-by-77-study-finds/7001599139929//print/
- Wang L, Song Y. Efficacy of zinc given as an adjunct to the treatment of severe pneumonia: a meta-analysis of randomized, double-blind and placebo-controlled trials. Clin Respir J. 2018; 12:857-864.
- Hopkins RG, Failla ML. Copper deficiency reduces interlukin-2 (IL-2) production and IL-2 mRNA in human T-lymphocytes. J Nutr. 1997: 127:257-262.
- Beck MA, Nelson HK, Shi Q, et al. Selenium deficiency increases the pathology of an influenza virus infection. Faseb J. 2001; 15:1481-3.
- Broome CS, McArdle F, Kyle JA, et al. An increase in selenium intake improves immune function and poliovirus handling in adults with marginal selenium status. Am J Clin Nutr. 2004; 80: 154-162.