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What is the Immune System and how to boost your immunity through diet

About the author

Maddie Smith has a DipCNM in Nutrition Therapy from the college of Naturopathic medicine and is a Sports Massage Therapist at the Bristol Chiropractic Sports and Family Clinic.

Healthy food to boost immunity including fish, nuts, avocado, cheese, strawberrries

The human immune system is constantly interacting with the body's internal environment, while also protecting it from the external environment and providing the knowledge necessary to tell the difference between friend and foe. Some people have an overactive immune system and others an underactive immune system. This can be due to a variety of factors, from genetics to individual health, and can lead to a myriad of health concerns such as allergies, infections, and more serious diseases such as cancer. Now more than ever, we are searching for ways that we can boost our immunity and stay safe in our daily environment.

What is the immune system?

The immune system is a network of components, from organs such as bone marrow to white blood cells and antibodies, that interact with each other to protect us from viruses, bacteria, yeasts, fungi, and other foreign substances.

It provides two types of immunity:

Innate (non-specific) immunity

two hands touching skin
Innate (non-specific) immunity such as skin

Innate (non-specific) immunity - This is the first line of defence against pathogens such as our skin, mucus membranes and substances within our tears and saliva. This response acts quickly (within hours) and provides the same defence for all pathogens hence the name 'non-specific'.

Adaptive (specific) immunity

blood samples testing
Adaptive (specific) immunity including white blood cells and antibodies

Adaptive (specific) immunity. The second line of defence that takes over if the innate immune system is unable to destroy the pathogens. This includes antibodies and white blood cells. Adaptive immunity is slower as it first needs to identify the pathogen, however, it is more accurate and has the ability to remember the germs, so it can respond faster if there is a second encounter with the pathogen. The ability to remember is also why there are some illnesses that we can only get once, such as chickenpox.

What are the different types of immune disease?

Problems can occur when the immune system is not functioning properly. Some are mild, such as allergies, and others can be much more severe, such as genetic disorders that destroy the function of immune cells.

Disorders of the immune system can be divided into three main categories:

Immune Deficiency

Immune Deficiency - these disorders can be temporary. For example, patients receiving chemotherapy, bone marrow transplants, or immunosuppressant drugs will experience a weakened immune system until proper cell population/function is restored. There are also permanent immunodeficiency conditions known as PIDDs (Primary Immune Deficiency Diseases). These are inherited genetic disorders and although they are rare, they can cause chronic vulnerability to infection. HIV is another kind of immune deficiency disorder that specifically infects white blood cells, allowing secondary infections to occur.


Woman sneezing due to allergies
Allergies are one type of immune system disorder

Allergies - this is a form of overactive immunity. An allergy is a hypersensitive reaction to common environmental substances such as pollen or food. These reactions are divided into four classes: Class I, II, and III are caused by an overproduction of antibodies by B cells (a type of white blood cell) that activate other immune cells, which in turn release inflammatory substances such as histamine. Class IV are caused by T cells (another white blood cell), which may cause damage to themselves or other cells.


person testing finger for autoimmune disease Type 1 diabetes
Type 1 diabetes is an organ specific autoimmune disease

Autoimmunity - this occurs when self-tolerance is broken, meaning the immune system has lost the ability to distinguish between self-produced antigens and foreign antigens. Autoimmunity can be organ-specific or systemic (affecting the entire body). For example, Type 1 diabetes is an organ-specific condition caused by immune cells believing insulin-producing pancreatic cells are foreign. By contrast, Systemic Lupus Erythematosus (more commonly known as Lupus) is a condition where the antibodies recognise and attack antigens produced by healthy cells - in other words, the immune system injures the body’s healthy tissues.

Impact of nutrients on immunity

Adequate nutritional intake is required for all cells to function correctly, including immune cells. When the immune system has been activated i.e., in the event of an infection, the immune system increases the demand for energy. Therefore it is important to have an intake of nutrients that support the proper function of immune cells, which will allow them to provide an effective response against pathogens as well as the ability to quickly settle this response when required to avoid any underlying inflammation.

The immune system’s requirements for energy and nutrients can be met through exogenous sources such as the diet or endogenous sources such as the body’s own stores.

Some micronutrients and other dietary constituents have specific roles in the development and preservation of a properly functioning immune system. For example, arginine (an amino acid) is essential for the production of nitric oxide by macrophages (another type of white blood cell), which is vital for protection against infectious organisms and for the regulation of many other immune cells. Similarly, the micronutrients vitamin A and zinc are essential for the immune system as they regulate cell division and contribute to successful proliferative response by immune cells.

It is well known that inadequate nutrition will impair immune function and the extent of this will depend on the severity of the nutrient insufficiency, whether infection is present, and the age of the individual. A single nutrient can produce a variety of different immunological effects, such as vitamin E; it works as an antioxidant, an inhibitor of protein kinase C activity (overactivity of which contributes to various mental health disorders) and interaction with enzymes and transport proteins. Excessive intake of some micronutrients can result in impaired immune response, for example excessive iron supplementation can contribute to increased risk of infection due to defective chemotaxis (migration of cells) and phagocytosis (process and elimination of cells) of neutrophils and macrophages, as well as reduced natural killer cell activity.

In addition to nutritional intervention effectively treating immune deficiencies that are related to poor nutritional intake, it is thought that specific nutrient intervention can enhance immune function in sub-clinical conditions, therefore preventing the onset of infections or chronic inflammatory disease.

How to boost Immunity through diet

The following are some examples of nutrient rich foods or meals that can provide some support to the immune system:

Bone broth - supports immune function by maintaining gut health and reducing gut inflammation. Provides collagen and amino acids (proline, glutamine and arginine).

Ginger - Ayurvedic medicine has been using ginger for its immune boosting effects for centuries. Ginger root has been used successfully in various intestinal disorders due to its antibiotic effect. Also an effective anti-inflammatory, it has been shown to reduce inflammation in conditions such as osteoarthritis and rheumatoid arthritis as well as reducing symptoms such as swelling and joint pain.

Green tea - the polyphenols within green tea (epicatechin and epigallocatechin) have a history of use as antioxidants. There is evidence to show that green tea extracts prevent oxidative damage in skin from exposure to UVB radiation. The antioxidant effects of green tea are not dependent on the presence of caffeine, so those who are sensitive to it can use decaffeinated green tea and still receive the same antioxidant benefits.

Citrus fruits - oranges, lemons, limes, tangerines and grapefruits are all excellent sources of vitamin C, which provides anti-inflammatory and antioxidant effects.

Yellow/orange/red fruit and veg and dark green leafy veg - such as carrots, pumpkin, sweet potato, red peppers, kale, spinach, collard greens. These are all excellent sources of the powerful antioxidant beta-carotene.

These foods contain a variety of beneficial vitamins and minerals that are known as micronutrients. Micronutrients contain specific properties that support various processes within the human body such as the proper functioning of the immune system. The following are some of the best micronutrients for supporting immunity:


vegetables and fruit full of vitamins

Vitamin A (Retinol or Beta-carotene)- Maintains good eye health and assists in the growth, repair, and protection of tissues through its involvement in the production of glycoproteins. It also stimulates cell growth in mucous membranes of respiratory and intestinal tracts as well as the skin, providing protection against infectious agents and environmental pollutants. It is also a powerful antioxidant, protecting cell membranes and tissue linings from harmful effects of free radicals by neutralising them. These antioxidant effects also protect the body from harmful pollutants such as smoke and therefore help prevent health issues such as ulcers and atherosclerosis. Food sources include: liver and fish liver oil for preformed vitamin A (retinol) and yellow or orange coloured vegetables and green leafy vegetables for beta-carotene.

Vitamin C (Ascorbic acid) - Needed for the formation of collagen and therefore provides support for connective tissue production, wound healing, and maintaining healthy blood vessels. Essential for the production of adrenal hormones and lymphocytes and has a direct effect on bacteria and viruses. Food sources include: citrus fruit, rose hips, papaya, acerola cherries, red and green peppers, broccoli and tomatoes. Vitamin C is best obtained from fresh, uncooked food as it is a water soluble vitamin and is therefore easily destroyed in the cooking process.

Vitamin D (Calciferol) - Induces the production of antimicrobial peptides (short amino acid chains) by various immune cells, enhances chemotaxis (cell migration), the removal of damaged cells, and phagolysosomal fusion (combination of phagosome and lysosome, essential for destruction of pathogens) of immune cells in macrophages and monocytes and reinforces physical barrier function in many of the body’s cells. Vitamin D also has strong anti-inflammatory properties. For example, it upregulates anti-inflammatory cytokines and reduces the production of inflammatory cytokines, and it induces the change of macrophage polarisation from proinflammatory to anti-inflammatory. Vitamin D is also helpful in the case of autoimmunity. For example, it inhibits the differentiation and maturation of dendritic cells, which prevents autoimmunity and increases tolerance of self-produced antigens, and it inhibits B cell differentiation, proliferation and increases apoptosis (programmed cell death) in immunoglobulin producing B cells, which is important in auto-immune conditions where antibodies are predominant. Food sources of vitamin D are fairly minimal, with the flesh of fatty fish (such as salmon, trout or mackerel) and mushrooms being the best. However most dietary intake of vitamin D comes from fortified foods such as plant based milks. Therefore it is usually recommended for individuals to use a daily vitamin D supplement.

Vitamin E (Tocopherol) - interacts with vitamins A and C as well as selenium to provide antioxidant effects, such as stabilising cell membranes and protecting tissues of eyes, skin, liver, breasts, and testes, all of which are more susceptible to oxidation. It also protects lungs against oxidative damage from environmental substances and maintains biological activity of vitamin A. The best food sources are the oil components of all grains, seeds and nuts.


Zinc - boosts the immune response and possesses antiviral, antioxidant, anti-inflammatory, and wound-healing properties. It also has a protective effect on the liver. Zinc is responsible for regulating the functions of multiple enzymes and transcription factors that are important in a variety of biological processes such as immunity, growth, and development. Zinc is also important for maintaining the integrity of immune barriers. It supports cellular functions such as the growth and differentiation of innate immune cells, and it is involved in the production of antibodies. Food sources of zinc are fairly minimal due to mineral losses within soil and refining processes, therefore it is generally recommended to use a zinc supplement.

Selenium - essential for proper functioning of the immune system and reducing harmful oxidation of cells. It also regulates activity of innate and adaptive immunity in the presence of a virus. Selenium is part of an antioxidant system that protects against lipid peroxidation within cell membranes and intracellular structural membranes. Food sources of selenium include whole grains, nuts (such as brazil nuts), and molasses. Garlic, broccoli, onions, and mushrooms can also be good sources of selenium, but this is dependent on the quality of the soil in which they are grown. Other sources include shellfish (oysters, shrimp, clams, and crab) and fish (salmon and halibut).

Magnesium - vital for healthy physiological functions including immune responses. It is involved in nucleic acid production, DNA replication, leukocyte activation and antigens binding to macrophages. Magnesium influences both innate and adaptive immunity and it can protect DNA from oxidative damage. As it is a component of chlorophyll, dark green leafy vegetables tend to be the best food sources, but whole grains, nuts, seeds, and legumes are some other good sources of magnesium.

Herbal Medicine

Herbal medicines being made by a person wearing gloves

In addition to food, herbal remedies are praised for their influence on health and wellbeing including their immune enhancing properties.

Herbs have been used for their medicinal properties for centuries. Records of medicinal practises in Ancient Roman, Egyptian, Persian, Hebrew, and Native American cultures demonstrate the extensive use of herbs to treat every known illness. The pharmaceutical industry was originally based on the process of extracting potent ingredients from various herbs that aid healing and making them available in a purer form. Herbalists believe that herbs also contain less powerful ingredients that counterbalance the more potent substances, therefore herbs are better used in their complete form.

Echinacea - enhances lymphatic function. Echinacea supplements have been studied for their ability to reduce common cold symptoms and were found to be 60% more effective than a placebo.

Black radish, dandelion, and milk thistle - help cleanse the blood of harmful substances and liver to support proper detoxification function.

Astragalus - powerful antioxidant which generates anti-cancer cells in the body.

Ginkgo Bilboa - boosts brain cell health, aids circulation and acts as a powerful antioxidant.

Other remedies

Probiotics - The benefits of probiotics for disease are widespread. The most prominent effects of probiotics on health is the regulation of immune response. An unbalanced immune response can lead to inflammation and tissue damage, which may result in disease. An individual's mucosal immune system will sense the intestinal microbiota, which is significant for maintaining intestinal balance and inducing a systemic immune response. Therefore, addressing the intestinal microbiome is a potential approach for supporting health and preventing illness or disease. Probiotics regulate innate and adaptive immune responses by maintaining the functions of various immune cells (dendritic cells, macrophages, and T and B lymphocytes) and the activation of toll-like receptors (key proteins in innate immunity). There are several benefits of probiotic use and the intestinal defence system including:

Dietary advice for immunity against COVID-19

Coronavirus covid 19 molecule floating

Now more than ever we are searching for ways to boost our immunity in order to provide some protection against the current coronavirus pandemic. Many of the previously discussed micronutrients possess strong antiviral properties, and some specific examples are set out below:

As stated previously in this article, vitamin D has crucial implications in the proper functioning of our immune system. It is also important to note that low levels of vitamin D can increase the risk and severity of respiratory conditions such as asthma, rhinitis, pulmonary conditions, viral respiratory infections, and also potentially the COVID-19 virus. Vitamin D has been shown to influence lung structure, size, volume, and function, and as such a deficiency in this vitamin could worsen respiratory conditions such as COVID-19. Recent studies have shown that individuals taking daily supplementation of vitamin D had a reduced risk of developing a respiratory infection.

A deficiency in vitamin C is associated with an increased risk and severity of respiratory infections such as pneumonia. There is evidence to suggest that oral supplementation of vitamin C can shorten the symptoms of the common cold in children and reduce the occurrence of pneumonia amongst the elderly. The treatment with intravenous vitamin C has been shown to reduce the recovery time of patients with virus-induced acute respiratory distress syndrome. This suggests that vitamin C is a practical option for the management of COVID-19.

Vitamin A deficiency is a risk factor for increased vulnerability to viral respiratory infections. Vitamin A supplementation has been shown to reduce the occurrence of Mycoplasma pneumoniae infection, a post-viral secondary bacterial infection in COVID-19. This indicates that having optimal levels of vitamin A would be helpful in protection from viral infections such as COVID-19.

While deficiency of vitamin E is rare in humans, supplementation has been shown to improve overall immune function, reduce occurrence of respiratory tract infections, and lower the viral load in lung tissues. Therefore, those with poor nutrition could benefit from vitamin E supplementation for the protection against COVID-19.

Zinc has multiple direct and indirect antiviral properties. For example, a specific zinc ionophore (chemical that reversibly binds ions) inhibits an enzyme that promotes the replication of SARS-CoV-2, the virus behind COVID-19. Supplementation of zinc has been shown to reduce the susceptibility, symptom severity, and duration of common colds and viral pneumonia, suggesting that it could be beneficial in the protection against viruses such as COVID-19.

Deficiency in selenium can result in an abnormal immune response and excessive cytokine production, which can in turn increase the risk and severity of virus-induced pulmonary infections. Optimal levels of selenium increases the effect of innate antiviral immune responses for reducing the pathogenicity of viral infections such as the flu, and supplementation of selenium in deficient individuals increases the immune response to viruses. This indicates that optimal intake of selenium can help protect against COVID-19 virus.

Insufficient levels of magnesium can increase an individual's vulnerability to upper respiratory tract infections as well as encouraging the production of pro-inflammatory cytokines, acute-phase proteins and free radicals, which will result in increased inflammation. Optimal levels of magnesium contribute to maintenance of healthy lung structure and function, suggesting that it could provide some protection against COVID-19.

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