The COVID-19 pandemic has led to claims that certain foods and supplements can boost immunity. Although optimal nutrition provides fuel for immune system function and contains antibacterial, antiviral, and immunoregulatory nutrients which support immunity, some researchers claim these efforts don’t actually work.

Immune impairments associated with nutritional inadequacy increase susceptibility to infection and enable infections to progress, yet its role in strengthening immunity remains complex.

Vitamin A

Vitamin A is essential to our immune systems, found both in plant and animal products. It has been known to stimulate white blood cell production which are key in protecting us against pathogens like bacteria. Furthermore, Vitamin A regulates our innate and adaptive immunity – providing protection from infections such as tuberculosis or pneumonia.

Studies have demonstrated that vitamin A deficiency can result in the breakdown of mucosal barriers, making individuals more prone to infection. It’s especially prevalent among children and can increase susceptibility to infections like diarrhea, pneumonia and measles [21-22]. It has also been shown that correcting vitamin A deficiency among children may reduce mortality from infections by approximately 30-35% [22-25].

VitA also helps regulate oxidative stress of the immune system. Under such pressure, immune cells produce cytokines which damage themselves as well as release them into surrounding tissue – these cytokines can be blocked with VitA presence to minimize oxidative stress [23].

VitA plays an integral part in an intricate bi-directional mechanism in our gut that promotes immune tolerance, which allows us to consume an assortment of foods without adverse reactions. Because VitA plays such an essential role, it is especially important that we include in our diet an abundance of foods containing ample vitamin A.

Vitamin A-rich foods include liver, fish oils, leafy green vegetables, tomatoes, dairy products and many fruits and vegetables. Many breakfast cereals and juices also fortify them with it and supplementation can provide it via preformed retinol (preformed Vitamin A) or carotenoids such as beta-carotene lutein and zeaxanthin.

Vitamin C

Vitamin C is a water-soluble vitamin found naturally in fruits and vegetables. As one of our most powerful antioxidants, it works to prevent damage that could lead to some cancers, cardiovascular disease and other health conditions. Furthermore, Vitamin C also plays a vital role in wound healing processes and the production of many hormones and chemical messengers used by our nervous systems.

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Vitamin C deficiency is uncommon; however, malnourishment, alcohol abuse disorder and smoking can all decrease vitamin C levels significantly, potentially leading to scurvy — an illness marked by chronic skin and joint issues as well as poor wound healing.

Vitamin C acts as an antioxidant, providing protection from oxidative stress. Furthermore, leukocytes – immune cells responsible for clearing out infections- recognize and dispose of microbes through leukocyte activation; leukocyte activity then supports production of interferons – antiviral and antibacterial cytokines with powerful antimicrobial effects – as well as interferon production increase with vitamin C supplementation.

Studies have suggested that diets high in foods containing vitamin C can lower the risk of cancer, including colon and rectal cancer; however, more research needs to be conducted. Furthermore, vitamin C has also been suggested as helping decrease stroke risks by hindering atherosclerotic plaque development.

Another study showed that increased intake of vitamin C through diet was associated with decreased risks of stomach cancer among those infected with Helicobacter pylori (Stomach Cancer) (72). Laboratory experiments indicate that vitamin C inhibits formation of carcinogenic N-nitroso compounds in the stomach; further research is necessary to ascertain whether supplemented vitamin C could provide similar protection as eradication therapy for pylorus infection.

Vitamin D

Vitamin D interacts with receptors on immune cells to activate production of antiviral peptides known as cathelicidin and defensins that strengthen innate immunity against infection. Furthermore, supplementing vitamin D may prevent overzealous adaptive immune responses that lead to autoimmune conditions like Lupus.

Studies of diet consumptions have shown that adequate vitamin D intake reduces the incidence of upper respiratory tract infections such as influenza. Other research indicates that infants with lower levels of Vitamin D are more likely to be hospitalized for respiratory illnesses like pneumonia; supplementation can decrease both duration and severity of such infections.

Low vitamin D stores have been linked with an increased risk of infections like tuberculosis (TB), inflammatory bowel disease, type 1 diabetes, cardiovascular disease (CVD) and depression. Vitamin D metabolites may play an integral part in controlling blood pressure regulation, vascular cell growth and even inflammation and fibrosis pathways.

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Research funded by NIEHS has demonstrated that diet modifications – specifically adding in more zinc and folic acid – can significantly lessen the effects of an autoimmune condition known as Lupus, in which your immune system attacks its own tissues and organs. Nutrition can also help improve multiple sclerosis and rheumatoid arthritis disorders; additionally stress reduction techniques, healthy ways of dealing with stress management as well as eating nutritiously-dense food choices along with drinking plenty of water and getting adequate rest are beneficial in supporting immunity.

Vitamin E

Vitamin E is an antioxidative that provides protection for cells against oxidative damage and increases immunity system cells’ effectiveness. Its key role in combatting oxidative stress likely involves its ability to scavenge reactive oxygen species while increasing glutathione peroxidase (GPx) activity (1). Lack of vitamin E has been associated with higher risks for chronic diseases, including cardiovascular disease and cancer (2); women enrolled in Women’s Health Studies with serum concentrations within the top quintile for a-tocopherol had 35% reduced risks for venous thromboembolism than those within lower quintile (3)

Test-tube studies conducted with vitamin E demonstrated its ability to increase T cell function (4). This was due to redistribution of membrane associated signaling proteins such as linker for activation of T cells family member 1 (LAT), tyrosine-protein kinase ZAP70 and phospholipase Cg; additionally it improved CD4+ T cell subset and increased antigen-specific T cell deployment (5).

Although eight fat-soluble vitamins, known as tocopherols and tocotrienols, meet the RDA, only a-tocopherol is commonly found in food and human plasma – and therefore fulfills it (6). Absorption occurs via small intestinal absorption into fat-soluble compounds called chylomicrons that contain this form.

Severe vitamin E deficiency is uncommon among humans but has been linked with certain genetic defects that hinder transport of a-tocopherol through its transfer protein or lipoproteins (20). Furthermore, this condition has also been seen among patients suffering from fat malabsorption syndromes that prevent proper absorption of fatty acids, and therefore vitamin E (21). Supplementation with supplemental a-tocopherol can prevent carcinogenesis through its antioxidant properties; for instance a study conducted among smokers demonstrated this via their Supplementation significantly reduced lung cancer incidence among this group (22).

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Iron

Iron is an essential micronutrient in helping the immune system react effectively against invading microbes, according to recent scientific studies. Iron has been demonstrated as essential for T-lymphocyte proliferation and maturation (immune system white blood cells that help destroy infected or diseased cells and make antibodies), as well as for sequestering iron away from infectious organisms by binding it with proteins like lactoferrin or transferrin binding agents and thus making it unavailable to them.

Studies published in Med suggest that low amounts of iron may impede our body’s ability to respond effectively to vaccines. Researchers observed that mice with high levels of the hormone hepcidin and low serum iron had less effective immune responses to vaccines, including less effective memory T-lymphocyte production – essential for remembering infections and providing adaptive responses against them in future outbreaks.

Diet is vital to maintaining robust immunity. A diet containing adequate amounts of key vitamins and minerals – as outlined by our Healthy Eating Plate – is key for keeping immunity strong; but some groups are especially at risk from deficiency of certain essential vitamins and minerals, including seniors whose immunity declines with age; women experiencing heavy menstrual bleeding; regular donors of blood; people living with chronic diseases taking medications which interfere with absorption or have increased needs as a result of illness or injury; as well as those who require extra nutrients due to illness or injury.

Consuming a well-rounded and varied diet rich in both animal (haem) and plant (non-haem) sources of iron is vital for overall good health. To optimize absorption of non-haem iron sources, consume them along with foods high in protein such as meat, fish or poultry; or vegetables which contain vitamin C like broccoli.