How to boost your immune system with diet: the importance of micronutrients
The human immune system is an intricate bodily network composed of cells, modular factors, and chemicals mediators and receptors that serves as a defense system against disease and external hits. Regardless, human nutrition and diet is indicative of the strength and efficiency of the immune system. Those with nutritional deficiencies have a poor and inefficient immune system which causes them to be more prone to develop viral infections, including the virus of the current epidemic, COVID-19. Further, if one develops a viral infection while having a poor immune system, their condition is likely to worsen.
Dietary protein is vital in strengthening the immune system. The building blocks of proteins are amino acids, which proliferate and activate the primary cells of the immune response, including T lymphocytes, B lymphocytes, natural killer cells, and macrophages. Amino acids additionally play a role in developing antibodies and phagocytic substances which prevent and manage viral infections, respectively. Foods high in dietary protein include cottage cheese, tuna, lentils, avocados, shrimp (although this option is weary for those who worry for their cholesterol), oats, quinoa, Greek yogurt, tofu, almonds, milk, and lean meats (Stephenson, 2001).
Most diseases are caused by inflammatory stimuli, which leads to inflammatory bodily processes; Vitamin C serves as an antioxidant that combats those inflammatory processes. Also, vitamin C targets and subsequently eliminates any free radicals that roam the biological system. This micronutrient helps in preventing cancer, heart disease, and slows the aging process. Vitamin C primarily accomplishes this by supporting epithelial barrier development of adaptive immune cells, aiding in white cell migration during immune responses, and directly leading microbial killing through production of phagocytic cells. Since there have been studies that have led to the belief that vitamin C consumption aids in respiratory rates and symptoms, there are studies being developed to investigate the association of vitamin C with COVID-19. (Stephenson, 2001). Foods high in vitamin C include tomatoes, melons, brussels sprouts, oranges, kale, apples, broccoli, grapefruits, kiwi, lemons, strawberries, blueberries, and acerola cherry (Very Healthy Life, 2017).
Vitamin A not only plays a key role in vision development, fetal development, and general growth; vitamin A is also crucial in bettering the state of the immune system. Vitamin A is especially important in the innate immune response because the micronutrient serves as an anti-inflammatory factor that protects mucosal barriers which protects the body from infections (BourBour, Dahka, et. al, 2020). Vitamin A deficiency leads to obstruction in the regeneration of mucosal barrier, natural killer cells, and neutrophils (Stephenson, 2001). This micronutrient additionally contributes to the phagocytic and oxidative activities of macrophages. Vitamin A has been known to decrease morbidity and mortality rates in infectious diseases, with the most well-known case being that of measles. Due to the anti-infection power of vitamin A, there are suggestions being made to opt it as a potential treatment and preventative factor for COVID-19 (BourBour, Dahka, et. al, 2020). Foods high in Vitamin A include cod liver oil, fortified skim milk, fortified breakfast cereal, carrots, sweet potatoes, yellow vegetables, broccoli, spinach, and dark green leafy vegetables (MedlinePlus, 2020).
Vitamin E is a fat-soluble antioxidant that is found in highest concentration in immune cells compared to other cell types in the blood. Hence, vitamin E plays a big role in modulating immune function. It is very rare to be deficient in vitamin E but consuming above the recommended daily allowance further enhances the state of the immune system; consuming above the recommended amount has been shown to reduce risk of infection, especially in the elderly population. Vitamin E modulates T cells, which protect the body from infection and types of cancer; vitamin E directly impacts the T cells by strengthening the cell membrane, improving the signal transduction pathway, and aiding in cellular division (Lewis, Meydani, et. al, 2018). Vitamin E additionally helps in reducing aging and prevents other degenerative diseases (BourBour, Dahka, et. al, 2020). Foods high in vitamin E include vegetable oils, almonds, peanuts, hazelnuts, sunflower seeds, spinach, broccoli, fortified breakfast cereals, and margarine (MedlinePlus, 2020).
Vitamin D is a steroid synthesized in the skin with the aid of sunlight. Multiple studies have reported that vitamin D aids in preventing respiratory infections. Vitamin D modulates innate cellular immunity by inducing antimicrobial peptides; antimicrobial peptides eliminate invading pathogens by rupturing their cell membranes and neutralizing their activity. Further, vitamin D reduces the expression of pro-inflammatory cytokines, while increasing the expression of anti-inflammatory cytokines (BourBour, Dahka, et. al, 2020); cytokines are proteins and signaling molecules that mediate inflammatory and immune responses (Sino Biological Inc, 2020). Also, vitamin D is known to reduce infection in the lungs as vitamin D metabolites regulate production of antibacterial proteins. Recent studies have shown that consuming vitamin D and melatonin can synergistically prevent and treat the pulmonary infection induced by COVID-19 (BourBour, Dahka, et. al, 2020). Foods high in vitamin D include salmon, tuna, trout, fortified milk, soy milk, almond milk, ham, fortified yogurt, orange juice, canned sardines, fish roe, eggs, and chicken (Very Healthy Life, 2020).
Iron is necessary for nearly all living organisms and aids in many important biological processes. Iron aids in both innate and adaptive immunity. However, iron is also the most dangerous micronutrient as excessive intake has been linked to an increase in degenerative diseases and infections (Nairz, Weiss, 2020). Regardless, iron consumption is imperative in humans as iron supplies oxygen to tissues and carbon dioxide to the lungs as part of the haeme protein, which is an essential protein of the haemoglobin. Iron can additionally alternate between oxidative states, making it play a major role in the transportation of the mitochondrial electron as a part of iron sulfur proteins and cytochromes. A good amount of research regarding the impact of iron on human health is still undetermined and up for debate, but some aspects have been proved for certain through multiple studies and trials (BourBour, Dahka, et. al, 2020). However, the amounts of iron consumed should be managed. Foods high in iron include dark chocolate, spinach, broccoli, red meat, baked potato, wild fish, chicken liver, dry thyme, pumpkin seeds, cashews, lentils, tahini, and black beans (Simply Health, 2020).
Zinc is essential in human normal development. Zinc helps with the function of cells that mediate innate immunity; zinc additionally modulates neutrophils, a type of white blood cell. Zinc deficiencies affect macrophages, the phagocytic process, intracellular killing, and cytokine production. Further, zinc deficiencies cause a decrease in growth of functional T and B cells, which are the primary cells in the immune response (Prasad, 2008). Apart from this, zinc plays a major role in optimizing antioxidant function, which is key in keeping the immune cells and other immune cellular components in normal state. Overall, all the bodily systems interact with one another which makes the role of dietary zinc major. Specifically, in the gut, dietary zinc interacts with copper, and levels of zinc are related to levels of copper; zinc induced copper anemia affects the bone marrow which subsequently reduces the precursors of immune cells (BourBour, Dahka, et. al, 2020). Foods high in zinc include dark meat chicken, cooked pork chop loin, cooked lobster, Alaska king crab, fortified breakfast cereal, beef patty, oysters, baked beans, lentils, oatmeal, firm tofu, low fat yogurt, and hemp seeds (Nall, 2019).
Selenium is essential for the effective operation of most bodily systems in both animals and humans; this is primarily due to the complex biochemistry of selenium. Dietary selenium influences both the innate and adaptive immune response. As noted, T cells and B cells are crucial in the adaptive immune response. Selenium-deficient T cells and B cells are less able to reproduce in response to mitogen and macrophages. Further, selenium deficiency results in greater adhesion between neutrophils (crucial white blood cell type in innate immune response) which causes damage to the acquired immune response (Skrajnowska, Bobrowsla-Korczak, 2019). Also, selenium works synergistically with vitamin E in antioxidant activity. Hence, selenium is complementary to vitamin E; vitamin E deficiencies and selenium deficiencies are typically observed simultaneously. Regarding the antioxidant activity, selenium helps protect lipids, proteins, and all other intracellular biomolecules from mercurial oxygen attacks. Foods high in selenium include tuna, halibut, sardines, ham, baked beans, oatmeal, milk, yogurt, cottage cheese, beef liver, rice, cashew nuts, peaches, carrots, lettuce, and bananas (National Institutes of Health, 2020).
Vitamin B6 and B12
Vitamin B6 is essential for optimal health and necessary to strengthen immunity. A deficiency in vitamin B6 leads to a decrease in Interleukin-2, which is a type of cytokine signaling molecules in the immune system that regulates the activities of white blood cells; hence, deficiency in vitamin B6 leads to impairment of the immune responses. Vitamin B6 deficiency is additionally linked to inflammation, various types of cancers, and many other diseases. Vitamin B12 is a micronutrient produced by bacteria in the colon. It is very common for vegans or for those who follow a plant-based diet to have a deficiency in vitamin B12, since it is not found in foods of plant origin. Since vitamin B12 plays a large role in general cellular division, it also plays a role in human immunity by efficiently developing T cells and maintaining normal cell and lymphocyte counts (BourBour, Dahka, et. al, 2020). Foods high in vitamin B6 include milk, bananas, fortified breakfast cereals, peanuts, soya beans, oats, poultry, pork some types of fish, and wheatgerm. Foods high in vitamin B12 include meat, fish, milk, fortified breakfast cereals, eggs, and cheese (NHS, 2020).
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