Nutritional Perspectives: The role of optimal nutrition for managing the current COVID-19 pandemic cannot be underestimated. Nutrition has a demonstrable role in the prevention and treatment of moderate to severe respiratory and non-respiratory infections. Adequate nutrition is even more essential for marginalized communities and in low- and middle-income countries, where deficiencies in key vitamins and minerals expose individuals to greater morbidity and mortality.
Worldwide, there is an array of clinical trials under way to evaluate treatment options against coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus.
NUTRITION AND IMMUNE DEFENSE
Micronutrients are dietary components that may contribute substantially to a robust immune system. Essential micronutrients like vitamins A, D, E, C, B6, B12, and folate and trace elements such as iron, zinc, and selenium, available in a variety of fresh animal- and plant-based foods, aid the body’s ability to fight infections.
Health and survival are increasingly dependent on the functioning of the immune system. Mechanistically, a rapid innate immune response occurs through phagocytes when a pathogen assaults the living system, but an adaptive immune response more specifically identifies the invading pathogen.
A strong immune system no doubt ensures host defense against pathogens and neoplastic cells, and balanced nutrition augments the immune system to provide optimal defense against infectious agents.
IMMUNE-BOOSTING ROLE OF VITAMINS
Vitamin A is capable of defending the body against a variety of infections, primarily by regulating the proliferation and differentiation of immune cells. Supplementation with preformed vitamin A has been suggested to downregulate the secretion of proinflammatory cytokines like tumor necrosis factor α and interleukin 6 in response to infections. The anti-infective role of vitamin A has been described in a number of studies that suggest all-trans retinoic acid to function via the nuclear retinoid acid receptor amongst others.
Vitamin A is essential for maintaining normal bodily functions, including defense against infections. An inadequate intake of vitamin A–rich food results in vitamin A deficiency, thus necessitating supplementation.
As cofactors to enzymes, B vitamins are central to the formation of, and the energy metabolism in, certain organic molecules. Multiple studies have suggested a significant role of B vitamins, eg, folic acid, B12, and B6, in the function of the immune system.
Scientific reports validate the significant role of vitamin B in normal function of the immune system, including the direct regulatory effects of vitamin B on immune response. Among its myriad immune-promoting features, vitamin B3 has been shown to inhibit neutrophil infiltration in the lungs, indicating an anti-inflammatory effect during ventilator-associated lung injury.
A plethora of scientific literature supports the role of vitamin C as an immune booster. Besides exerting antioxidant activity, supplementation with ascorbic acid significantly affects epigenetic regulation and cell signaling. The potential role of vitamin C as an antiviral agent against coronavirus has been observed in animal models which outlined several immune-supporting features of vitamin C, including involvement in phagocytosis, antibody production, growth and functioning of immune cells, and transitioning of leukocytes at infection sites. There is also evidence for the role of vitamin C as a weak antihistamine agent to reduce symptoms of stuffy nose and swollen sinuses.
Vitamin D has the ability to foster differentiation of monocytes to macrophages, which destroy invading agents. The formation of special antimicrobial proteins is regulated by certain vitamin D metabolites, and these antimicrobial proteins play a substantial role in combating infections, including lung infections, by destroying pathogens.
Respiratory tract infections can severely exacerbate chronic diseases, leading to increased risk of death. Vitamin D can act through several mechanisms to decrease the risk of respiratory infections, including pneuomonia.
As a potential antioxidant, vitamin E has the capacity to protect cells and their functional components from injury caused by the release of reactive oxygen species that occurs during immune reactions to invading pathogens in respiratory infections. Vitamin E is involved in multiple aspects of the immune response, including phagocytosis, the production of antibodies, and T-cell proliferation.
TRACE MINERALS FOR A WELL-FUNCTIONING IMMUNE SYSTEM
Trace minerals are an essential component of the diet. Their regulatory effects on immune function have been well defined, and inadequate levels of trace elements have been reported to alter immune competence in humans. Prolonged dietary deficiencies of trace minerals may result in impaired immune function by influencing one or more components of the immune system.
Zinc, as a co-factor, is an integral component of more than 300 enzymes that exert secondary effects on the human immune system. Effects of zinc on the immune system are multifaceted.
The impact of zinc on immune mediators like enzymes, cytokines, and thymic peptides has also been reported, suggesting that recommended dietary intake or supplementation of zinc is essential to prevent functional loss.
Zinc deficiency in the elderly can lead to decreased or diminished T-cell response, reduced natural killer cell activity, and depressed thymic hormone levels, thus creating substantial risk for respiratory infections and their associated morbidity and mortality.
The substantial role of iron in the immune response has been widely documented in the literature, with iron deficiency shown to lead to impairment of the host immune system.
Adequate iron intake influences the innate immune response of the host by mediating the nuclear factor κB (NF-κB) and interferon γ (IFN-γ) signaling pathways in macrophages. The metal enhances the host’s ability to resist intracellular pathogens.
IMMUNE DEFENSE AND NUTRITIONAL NEEDS OF OLDER ADULTS
Immunosenescence, or the progressive deterioration of the immune response in aging, affects both innate and adaptive immunity in various pathological conditions, resulting not only in increased susceptibility of older adults to infections but also a reduced response to various treatment regimens, including vaccines.
Undoubtedly, immunocompromised older adults with additional comorbidities constitute a population at high risk of infection and severe morbidity. More drastic outcomes have been observed during the ongoing COVID-19 pandemic: data confirm older adults as the most vulnerable population, with mortality reaching up to an estimated 15%.
Older adults, compared with younger populations, are more susceptible to COVID-19–like viral infections and their associated serious outcomes. This increased susceptibility is attributable to aging-associated physiological changes, a weakened immune response, malnutrition, and multi-morbidities. Prolonged hospitalization to ensure the stabilization and recovery of COVID-19 patients increases the risk of malnutrition and severe loss of lean body mass and muscle function. Nutritional screening and treatment of malnutrition in older patients is therefore mandated as part of COVID-19 patient care.
Factors predicted to be associated with high risk of severe COVID-19 include age above 50 years, male gender, smoking, chronic kidney disease, diabetes, cardiovascular disease, chronic obstructive pulmonary disease, and cerebrovascular disease. Individuals with these risk factors should be screened for micronutrient deficiencies. Supplementation to achieve adequate serological levels of the deficient nutrients may be provided in accordance with in-practice guidelines. The impact of supplementation should be evaluated relative to reductions in the severity of infection and improvements in the recovery index.
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