Some nutrients play key roles in maintaining the integrity and function of the immune system, presenting synergistic actions in steps determinant for the immune response. Among these elements, zinc and vitamins C and D stand out for having immunomodulatory functions and for playing roles in preserving physical tissue barriers. Considering the COVID-19 pandemic, nutrients that can optimize the immune system to prevent or lower the risk of severe progression and prognosis of this viral infection become relevant. Thus, the present review aims to provide a comprehensive overview of the roles of zinc and vitamins C and D in the immune response to viral infections, focusing on the synergistic action of these nutrients in the maintenance of physical tissue barriers, such as the skin and mucous membranes. The evidence found in the literature shows that deficiency of one or more of these three elements compromises the immune response, making an individual more vulnerable to viral infections and to a worse disease prognosis. Thus, during the COVID-19 pandemic, the adequate intake of zinc and vitamins C and D may represent a promising pharmacological tool due to the high demand for these nutrients in the case of contact with the virus and onset of the inflammatory process.
Several minerals and vitamins have antioxidant, immunomodulatory and antimicrobial roles which could be helpful for the immune response against the SARS-CoV-2 virus. In the absence of a widely available treatment or a vaccine for COVID-19, supplementation of micronutrients emerges as an important measure to improve the immune system and to prevent the development of severe symptoms. Some of these micronutrients are the vitamins A, B, C, D and E, and minerals such as selenium, magnesium, and zinc.
The role of zinc, vitamin C and vitamin D for immunity was explored since these micronutrients show the strongest evidence for immune support. In this scenario, the mentioned studies demonstrate that zinc and vitamins C and D are integral parts of the immune system and show synergistic functions at various stages of the host defenses, such as the maintenance of the integrity of biological barriers and the functionality of cells that make up the innate and adaptive systems. Therefore, the deficiency or insufficiency of these key nutrients, acting in synergy in tight and adherents junction proteins, can lead to impairment of mucosal epithelial cells, possibly making them more susceptible to pathogen entry, such as SARS-CoV-2.
Overall, the medical literature demonstrates that the supplementation with zinc, vitamin C and vitamin D can mitigate viral respiratory infections. Thus, in the context of the COVID-19 pandemic, the supplementation with such nutrients may be characterized as a widely available, safe and low cost measure that can be useful to cope with the increased demand for these nutrients in case of contact with the virus and onset of the immune responses, as well as to lower the risk of severe progression and prognosis of this viral infection.