Dietary Supplements for Immune Function and Infectious Diseases

 Dietary Supplements for Immune Function and Infectious Diseases

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The immune system defends the body from pathogens that cause disease and is comprised of innate responses, which are the first line of defense, and adaptive responses, which become engaged later [1-3].

The innate immune system includes physical barriers, such as the skin and gut epithelium, that help prevent pathogen entry. It also includes leukocytes (white blood cells)—such as neutrophils, macrophages (which release cytokines), and natural killer cells—that attempt to find and eliminate foreign pathogens. However, these components are nonspecific, meaning that unlike the adaptive immune system, they do not recognize and respond to specific pathogens [1,2,4].

The adaptive immune system consists of B lymphocytes (B cells) that secrete antibodies (a process known as humoral immunity) and T lymphocytes, which are also known as T cells (a process known as cell-mediated immunity), both of which are pathogen specific [3-5]. The adaptive response takes several days or weeks to develop, but it generates immunological “memory”; as a result, a subsequent exposure to the same pathogen leads to a vigorous and rapid immune response [1,3,5]. Vaccinations stimulate the adaptive immune system, protecting the body from future exposures [2].

The body’s immune response to pathogens can lead to inflammation, causing redness, swelling, heat, pain, and possible loss of tissue function [6]. Inflammation helps eliminate the pathogen and initiate the healing process, but it can also cause symptoms and severe pathologies [6,7]. For example, activation of CD8 T cells as part of the adaptive immune response can increase inflammation and cause pulmonary damage. This process can lead to acute respiratory distress syndrome (ARDS), which has occurred in some patients with COVID-19 [7].

Consuming adequate amounts of several vitamins and minerals—including vitamin A, vitamin C, vitamin D, vitamin E, selenium, and zinc—is important for proper immune function, and clinical deficiencies of these nutrients weaken immunity and can increase susceptibility to infections [2,4,5,8-10]. Other ingredients (whether provided through foods or dietary supplements), such as botanicals and probiotics, are not essential in the body but might affect immune function.

Measuring the impact of dietary supplement ingredients, such as vitamins, minerals, or other substances, on the immune system is difficult because the immune system is a complex network of organs, tissues, and cells [11,12]. No single, straightforward measure of immune system function and resistance to disease exists. Indirectly, immune function can be assessed by examining a person's risk and severity of infectious diseases.

This fact sheet summarizes the effects of various dietary supplement ingredients on immune function and the risk of selected infectious diseases, including the common cold, influenza and other respiratory tract infections, infectious diarrhea, and HIV infection. These diseases can be caused by numerous pathogens. For example, the common cold is caused by a wide variety of respiratory viruses, most commonly rhinovirus, but also coronaviruses, adenoviruses, and other virus serotypes.