Diet and Infectious Disease - Does what we eat affect our risk of contracting illness?

In order to stay healthy, it is crucial that we avoid exposure to disease and practice preventive hygiene like handwashing. Additionally, maintaining a strong immune system is crucial for defending against infection, and nutrition certainly helps support immunity. Amidst the current coronavirus pandemic, many of us may wonder what specific nutrients play a role in fighting a disease like COVID-19. Research is limited on natural remedies specifically for coronavirus, but there is information indicating positive effects of various vitamins and minerals on preventing or treating infectious illnesses.

​Vitamin D is found in dairy products, egg yolks, and fatty fish, like salmon. However, the best source of vitamin D is exposure to sunlight - just 10 to 15 minutes of sunshine on the arms and legs each week can generate enough vitamin D to meet most adults’ needs. For individuals living in Northern parts of the world, sun exposure may not be adequate to synthesize enough vitamin D, so a vitamin D supplement may be appropriate to maintain optimal health. Research demonstrates that in people who are vitamin D deficient, adding a moderate vitamin D supplement may reduce the risk of respiratory infection (1). 

N-Acetyl Cysteine (NAC) is the supplemental form of cysteine, an amino acid found in protein-rich foods like pork. NAC is needed to regenerate glutathione, an important antioxidant that serves to prevent cellular damage. A clinical study demonstrated that twice daily supplementation with NAC reduced symptoms in people with the flu (2).

Polyphenol compounds are found in a variety of plant foods and are especially rich in deeply pigmented fruits, such as elderberries. Black elder has been used for centuries as a treatment for viruses and is one of the most popular medicinal plants worldwide. Some preliminary research suggests that elderberry extract may reduce the duration of the flu.

Vitamin C is necessary for white blood cell function and enhances iron absorption. Iron deficiency is common among women and dancers, and inadequate levels can increase susceptibility to infections. While adequate vitamin C intake is important for immune function, mega-doses can lead to adverse side effects, such as upset stomach, diarrhea, and interference with medications. Rather than supplementing vitamin C, consider a food-first approach by including several servings per day of fruits and vegetables. Foods rich in vitamin C include kiwi, citrus, bell peppers, berries, strawberries and Brussel’s sprouts. 

Zinc has anti-viral properties and certain zinc supplements have been shown to reduce the severity and duration of colds (3). Laboratory studies suggest increasing intracellular zinc concentration can impair the replication of a variety of viruses, including influenza and SARS-CoV. Zinc may not prevent infection entirely, but adequate intake certainly supports immune function. Keep in mind that excessive supplementation with zinc may interfere with copper absorption, so limit use of zinc lozenges to once a week. Natural sources of zinc include legumes, nuts, whole grains, seeds, meat and shellfish.

For more information about COVID-19, check out the Centers for Disease Control and  the World Health Organization’s Myth Busters.

1. Carlos A. Camargo, Davaasambuu Ganmaa, A. Lindsay Frazier, Franca F. Kirchberg, Jennifer J. Stuart, Ken Kleinman, Nyamjav Sumberzul and Janet W. Rich-Edwards. Randomized Trial of Vitamin D Supplementation and Risk of Acute Respiratory Infection in Mongolia. Pediatrics September 2012,  130 (3) e561-e567; DOI: https://doi.org/10.1542/peds.2011-3029
2. De Flora S1, Grassi C, Carati L. Attenuation of influenza-like symptomatology and improvement of cell-mediated immunity with long-term N-acetylcysteine treatment.  Eur Respir J. 1997 Jul;10(7):1535-41. 
3. Hemilä, H., Chalker, E. The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis. BMC Fam Pract 16, 24 (2015). https://doi.org/10.1186/s12875-015-0237-6.