Immune system activity is enhanced after a viral infection such as COVID-19

Although the immune system is always working to prevent pathogens from invading the body, as well as eliminating those pathogens and generating an immunological memory, the metabolic activity of immune cell types is enhanced following a viral infection such as COVID-19. That heightened activity is accompanied by a higher demand of energy and nutrients, which come from diet, to meet the immune cells’ requirements.

In a new comprehensive review, Prof. Philip Calder from the University of Southampton provides an update on the role of nutrition in supporting the immune system as part of the current fight against COVID-19.


Specific nutrients have the potential to modulate immune system activity through the gut microbiome

Different levels of evidence have shown the following as key nutrients involved in reducing infection risk by supporting antibacterial and antiviral defense:

  • Vitamins A, B6, B12, folate, C, D and E,
  • Trace elements including zinc, copper, selenium and iron,
  • Amino acids, and
  • Fatty acids.

The mechanisms by which each of the nutrients named above support the immune system include the strengthening of innate immune responses and antioxidant systems. Likewise, the gut microbiome also plays a role through its involvement in training the immune system and avoiding excessive inflammatory responses to pathogenic organisms. Furthermore, it has been shown to be altered in patients with COVID-19.

Although zinc and selenium have been shown to be particularly relevant for supporting antiviral defense, there is no single nutrient or diet that will prevent people getting infected with SARS-CoV-2 or have an impact on mortality in COVID-19. The immune system plays a central role in protecting against infection, but due to its complexity and the multiple ways in which it deals with viruses, the best advice is to consume a healthy, diverse and well-balanced diet that will provide the nutrients required to achieve a healthy gut microbiome, which can also benefit the immune system.

Considering that some patients with COVID-19 have been shown to have an altered gut microbiome, coupled with gastrointestinal symptoms, probiotics could be used as means of reducing bacterial translocation and secondary infection. However, even though probiotics containing Lactobacillus and Bifidobacterium have been shown to improve immune function and enhance the response to some vaccinations, it is still early to conclude whether the gut microbiome plays a therapeutic role in preventing or treating COVID-19.

In some COVID-19 patients, an excessive inflammatory reaction (called a ‘cytokine storm’) can occur as a compensatory reaction by immune cells for dealing with lung damage. In that regard, Philip Calder acknowledges in the review that the polyunsaturated omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) seem to be relevant in resolving ongoing inflammatory processes in patients with an outbreak of severe acute respiratory distress syndrome.


Are there any recommendations for what people should be eating during the COVID-19 pandemic?

Although there is no specific evidence that nutrients alone can help protect against or lessen the effects of COVID-19, eating well and keeping a healthy weight will help the immune system cope better with the demands placed on the body before, during and after COVID-19 infection.

The World Health Organization has stressed the importance of a balanced diet to maintain a strong immune system and to avoid or minimize infections during the COVID-19 outbreak. For instance, the WHO has recommended consuming 9 servings of fruit and vegetables per day, which is more than in the usual dietary recommendations.

Although micronutrients, nutraceuticals and probiotics could be of interest for enhancing immunity during the COVID-19 pandemic, it is too early to make specific recommendations due to the small number of intervention studies that have been published.

In particular, patients with malnutrition, diabetes, obesity, cardiovascular disease and respiratory disease—and especially older people—are at a higher risk of complications from COVID-19 and will require personalized nutrition advice. In an attempt to provide specific nutritional advice for supporting the proper functioning of the immune system, the International Society for Immunonutrition has suggested increasing the intake of vitamin E, zinc and vitamin C in older people, along with vitamin D if they have a low serum vitamin D status.

So far, the most effective way of limiting the spread of COVID-19 is by preventing contact between people. Although several vaccines have been developed for prevention of SARS CoV-2, mass vaccination roll-out will take months. Meanwhile, nutrition should be considered in any approach to ensure that individuals’ immune systems are well supported, even though no nutrition studies have been published yet in the context of COVID-19.



Calder PC. Nutrition, immunity and COVID-19. BMJ Nutr Prev Health. 2020; 3(1):74-92. doi: 10.1136/bmjnph-2020-000085.

World Health Organization. Nutrition advice for adults during the COVID-19 outbreak [cited 3 December 2020]. Available from:

Jayawardena R, Sooriyaarachchi P, Chourdakis M, et al. Enhancing immunity in viral infections, with special emphasis on COVID-19: a review. Diabetes Metab Syndr. 2020; 14(4):367-382. doi: 10.1016/j.dsx.2020.04.015.

Derbyshire E, Delange J. COVID-19: is there a role for immunonutrition, particularly in the over 65s? BMJ Nutr Prev Health. 2020; 3(1):100-105. doi: 10.1136/bmjnph-2020-000071.

International Society for Immunonutrition. ISIN Position Statement on Nutrition, Immunity and COVID-19. 2020 March [cited 2 December 2020]. In: ISIN [Internet]. Available from: