Optimizing your Immune system has perhaps never felt as critical as it does going into 2021. In 2020, we saw the emergence of the novel pathogen SARS-CoV-2, and the spread of its resulting disease, COVID-19. While this virus is novel, your immune system is anything but. In fact, your immune system has evolved over millions of years into an extremely complex and intricate network of cells and molecules that keep you alive on a daily basis. And, fortunately, there are steps you can take to help it function to the best of its ability.

Immune System Basics

All immunity can be broken down into two categories: innate and adaptive. Innate immunity is your body’s first line of defense. It involves a variety of cells that perform a variety of functions. These include ciliated respiratory epithelial cells that can physically push pathogens away, macrophages that engage in phagocytosis to engulf pathogens, granulocytic types of phagocytes such as neutrophils and basophils that secrete enzymes to destroy pathogens, and a type of lymphocyte known as the natural killer cell.[1] When innate immunity is unsuccessful at clearing a pathogen, it signals adaptive immunity to assist in the process. Adaptive immunity involves the activation of T and B lymphocytes, cells designed with the capacity to target pathogens in a manner specific to the pathogen at hand.

The Immune Response to SARS-CoV-2

When an individual comes into contact with SARS-CoV-2, their innate immune system will first attempt to clear the infection. One reason that SARS-CoV-2 is so infectious is that it has some unique features that make it especially good at evading innate immunity.[2] As a result of this, in many cases, the body will subsequently depend on adaptive immunity to fight the virus. During the adaptive immune response, T cells will help directly destroy cells infected with SARS-CoV-2 and will also stimulate B cells to produce antibodies to the virus and to virally infected cells.

The Importance of Vitamin D

Having sufficient levels of Vitamin D is critical to the function of the immune system and seems to be especially crucial in the case of fighting SARS-CoV-2. Cells involved in both the innate and adaptive immune response have been found to have receptors for Vitamin D, and the presence of Vitamin D enhances their function.[3] It has been noted the there is a correlation between Vitamin D levels and the severity of COVID-19 illness, namely that those who are deficient experience increased hospitalizations and increased mortality.[4] Vitamin D can be acquired from exposure to sunlight or UV lamps, as well as through diet and supplementation. It is estimated that around half the US population has insufficient levels of Vitamin D, although this can be easily addressed.

Why Sleep Matters

Sleep deprivation compromises the immune response while getting a sufficient amount of sleep enhances the immune response. Sleep deprivation is associated with a decreased number of lymphocytes and an increased susceptibility to several infections.[5] It has also been discovered that during sleep, T cells are better able to bind to their targets as a result of adhesion molecules, known as integrins, maintaining a “stickier” state.[6] According to the Center for Disease Control, one in three Americans are getting an inadequate amount of sleep.

How Diet Plays a Role

The diet we consume is essential to providing our immune system with the micronutrients needed to function properly. Perhaps the most well known of these micronutrients is Vitamin C, which is known to accumulate in phagocytic cells such as macrophages and neutrophils and enhance their ability to destroy infected cells via increasing chemotaxis, phagocytosis, and generation of reactive oxygen species.[7] 

Zinc is another micronutrient that is essential to proper immune function. Almost all immune cells involved in both adaptive and innate immunity show decreased function after Zinc depletion.[8] It is also important to get adequate amounts of Selenium from the diet, as immune cells use Selenium for a number of functions including protection from free radicals that are produced during the inflammatory response.[9] 

Iron is another crucial micronutrient, as it is required for immune cell proliferation and maturation.[10] Iron, Selenium, and Zinc can all be obtained by eating animal products such as beef, chicken, fish, and eggs. The foods with the highest Vitamin C content are fruits and vegetables. Of course, all of these micronutrients can also be obtained via supplementation.

The Significance of Exercise

Any discussion of strengthening immune function would be incomplete without mentioning exercise. Moderate-intensity physical exercise enhances the function of macrophages and increases the circulation of lymphocytes, anti-inflammatory cytokines, and even antibodies. Exercise also stimulates the exchange of immune cells between the circulatory system and tissues.[11] Intense exercise is not needed for this immunoprotective effect. One study found that individuals who walked a minimum of 20 minutes a day for a minimum of 5 days a week, had a 43% reduction in days with symptoms of respiratory infection when compared to those who exercised once a week or less.[12] Other studies have reported similar findings.

The Influence of Chronic Stress

Existing in a state of chronic stress is detrimental to the function of the immune system. Chronically stressed individuals have chronically elevated levels of cortisol and chronically elevated levels of cortisol are associated with a decrease in the number of lymphocytes. Many studies have shown that individuals who report being in a state of chronic stress are more susceptible to respiratory infections. In one of these studies, participants were given nasal drops containing rhinovirus and then quarantined and monitored. Those who were experiencing chronic stress were twice as likely to proceed to develop symptoms of rhinovirus, even after other factors such as age and BMI were accounted for.[13]

Vaccination As a Tool

Vaccines can assist in the body’s ability to fight infection by triggering an immune response to a pathogen that leads to the production of antibodies to that pathogen. These antibodies can then persist for years in the vaccinated individual and often prevent future infection. 

At the time of writing, the FDA has authorized the emergency use of two vaccines designed to protect against SARS-CoV-2 infection. These vaccines are the first vaccines to ever use mRNA as the means of triggering immunity. Both of these vaccines contain pieces of mRNA that encode a portion of SARS-CoV-2’s spike protein. When the body comes into contact with this mRNA, it translates it to create this piece of the spike protein. The immune system then recognizes the protein as foreign and antibodies are created against it.

It is worth noting that there have been studies that have shown that adequate levels of Vitamin D enhance the efficacy of various vaccines[14], that ample sleep does the same[15], and that proper nutrition and exercise also boost the likelihood of a vaccine being effective[16] [17].

Stay Healthy in 2021

We can’t change the fact that SARS-CoV-2 has emerged, but we can focus on optimizing our immune health and thereby decrease our chances of suffering a serious illness. By getting adequate sleep, achieving appropriate levels of Vitamin D, Vitamin C, Zinc, Selenium, and Iron, partaking in moderate exercise, and minimizing chronic stress, we aid our immune cells in functioning to the best of their abilities. Taking these steps also helps protect against many other infectious diseases. So, make the commitment today to prioritize your immune health and best wishes for a happy and healthy New Year!

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References:

[1] Gasteiger G, et al. Cellular Innate Immunity: An Old Game with New Players. J Innate Immun 2017;9:111-125.

[2] Taefehshokr N, et al. Covid-19: Perspectives on Innate Immune Evasion. Front Immunol 2020; 11:2549.

[3] Azrielant S, Shoenfeld Y. Vitamin D, and the Immune System. Isr Med Assoc J. 2017 Aug;19(8):510-511.

[4] Pereira M, et al. Vitamin D deficiency aggravates COVID-19: systematic review and meta-analysis. Crit Rev Food Sci Nutr. 2020.

[5] Besedovsky L, Lange T, Haack M. The Sleep-Immune Crosstalk in Health and Disease. Physiol Rev. 2019 Jul 1;99(3):1325-1380.

[6] Dimitrov S, et al. Gαs-coupled receptor signaling and sleep regulate integrin activation of human antigen-specific T cells. J Exp Med. 2019 Mar 4;216(3):517-526.

[7] Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017 Nov 3;9(11):1211.

[8] Ibs KH, Rink L. Zinc-altered immune function. J Nutr. 2003 May;133(5 Suppl 1):1452S-6S.

[9] Hoffmann PR, Berry MJ. The influence of selenium on immune responses. Mol Nutr Food Res. 2008 Nov;52(11):1273-80.

[10] Soyano A, Gómez M. Participación del hierro en la inmunidad y su relación con las infecciones [Role of iron in immunity and its relation with infections]. Arch Latinoam Nutr. 1999 Sep;49(3 Suppl 2):40S-46S.

[11] da Silveira MP, et al. Physical exercise as a tool to help the immune system against COVID-19: an integrative review of the current literature. Clin Exp Med. 2020 Jul 29:1–14.

[12] Nieman DC, et al. Upper respiratory tract infection is reduced in physically fit and active adults. Br J Sports Med. 2011 Sep;45(12):987-92.

[13] Cohen S, et al. Chronic stress, glucocorticoid receptor resistance, inflammation, and disease risk. Proc Natl Acad Sci U S A. 2012 Apr 17;109(16):5995-9.

[14] Sadarangani SP, Whitaker JA, Poland GA. “Let there be light”: the role of vitamin D in the immune response to vaccines. Expert Rev Vaccines. 2015;14(11):1427-40.

[15] Lange T, et al. Sleep after vaccination boosts immunological memory. J Immunol 187: 283–290, 2011.

[16] Hoest C, et al; MAL-ED Network Investigators. Evaluating associations between vaccine response and malnutrition, gut function, and enteric infections in the MAL-ED cohort study: methods and challenges. Clin Infect Dis. 2014 Nov 1;59 Suppl 4(Suppl 4):S273-9.

[17] Edwards KM, Booy R. Effects of exercise on vaccine-induced immune responses. Hum Vaccin Immunother. 2013 Apr;9(4):907-10.

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