Adequate nutrition promises a healthy immune system and malnutrition being the most common cause of immunodeficiency worldwide. A well-functioning immune system is critical for survival. Good nutrition is thus essential in supporting an optimum immune system, which can reduce the risk of viral infections. 

The immune system is a complex of cells, tissues, and organs that are specialized in defending against foreign agents. It is a remarkable defense mechanism and makes rapid, specific, and protective response against the innumerable potentially pathogenic microorganisms. 

Immunity through life cycle 

 In utero, the fetus gains   passive protection from its mother via antibodies, which cross the placenta. In early life, immunity is influenced by feeding practices and environmental exposure. Breast feeding provides passive immunity. In infancy diverse environmental factors such as pet ownership, antibiotic use and the timing of introduction of food impact development of immune system. A decline in immune function is seen in older adults making them more susceptible to infections. A number of micronutrient deficiencies have been identified as contributors to such declining immunity. 

The immune system is precisely a system, not a single entity. To function well, it requires balance and harmony. An activated immune system further increases the demand for energy & nutrients.  The increased demands can be met from diet or body stores.  Some nutrients and dietary components have very specific roles in the development & maintenance of effective immune system or in reducing chronic inflammation. 

Every part of our body, including our immune system, functions better when protected from environmental assaults and bolstered by healthy-living strategies which includes:

·        Nutrition therapy

·        Maintaining normal health and blood parameters

·        Sound sleep

·        Exercise and physical activity

·        Stress management (Yoga  & Meditation)

NUTRITION THERAPY

Nutritional deficiencies of energy, protein and specific micronutrients are associated with depressed immune function and increased susceptibility to infection. Providing a diet high in nutritious foods rich in vitamins and minerals supports optimal function of the immune system by providing antioxidants to slow damage of cells caused by free radicals or assisting in T-cell production. It is important to note that no single food is a superfood. A balance of macro and micronutrients is necessary for optimal functioning of the immune system.

MACRONUTRIENTS 

Carbohydrates (CHO): Carbohydrate is an important fuel cell for immune system. On the contrary high CHO diet affects immune system negatively. 

Fats:  Fats are important energy sources. Fatty acids are powerful modulators of immune response. Diets containing high amount of fats can also decrease cellular inflammatory activity and immune response. 

Proteins: Proteins make up the framework of body defense systems, enzymes and some hormones. Deficiency of essential amino acid can also cause repression on immune system. Latest studies have revealed   that protein metabolism play an important role in formation of natural and acquired immunity against infections.

MICRONUTRIENTS

Vitamin A:  Vitamin A increases resistance to infection by maintaining the integrity of barriers like skin and mucous membrane against bacteria, viruses and parasites. It enhances antibody production by WBC and increases the activity of T cells. Rich sources include carrot, pumpkin, dark green leafy vegetables, yellow or orange fruits and vegetables etc.

 Vitamin C: Vitamin C has an important role in wound healing and as an antioxidant. It also helps in protection against infections and inflammation by supporting various cellular functions of both innate and adaptive immune systems. Vitamin C also contributes to iron absorption.  Rich sources include red bell peppers, citrus fruits, papaya, green leafy vegetables, tomatoes etc. 

 Vitamin E:   By means of its antioxidant actions, Vitamin E protects WBC from oxidant damage during their immune response. It enhances antibody production by WBC and increases their ability to phagocytize bacteria. It increases resistance to viral and bacterial infections, especially among elderly. It also plays an important role in attenuating inflammation. Edible vegetable oils, green leafy vegetables, nuts, sunflower seeds, mango and legumes are good sources of vitamin E.

 Vitamin D:  Vitamin D plays important role in innate and adaptive immune system. Vitamin D supplementation has been found to suppress inflammation and decrease the incidence of acute respiratory tract infections.  For healthy children and adults, exposing the hands, face and arms on a clear summer day 10-15 minutes several times each week provides adequate vitamin D.

 Vitamin B6: Vitamin B6 is most needed for immune system among other group B vitamins. It is vital for supporting biochemical reactions in the immune system. Major sources include nuts (walnuts, peanuts), chickpeas, maize, whole grain cereals, banana, potato and other starchy vegetables.

 Vitamin B 9 (folate): Folate is essential in the development of RBC and for healthy cell growth and function.  Vitamin B12 and folic acid play important role in protein, DNA and RNA Synthesis. Hence they are closely related to immune system and inadequate levels impact immune response.  Sources include green leafy vegetables, orange, strawberry, lentils, yeast, wheat germ, peanuts etc. 

 Vitamin B12: B12 plays an important role in white blood cell production thus making it essential for proper immune system functioning. It works together with folate and Vitamin B6 and acts as an immune- modulator for cellular immunity.  In a vegetarian diet, milk and milk products are good sources.

 Iron (Fe): Low iron levels affect our ability to have an adequate immune response. Iron is required for immune cell production and growth, particularly lymphocytes. An abnormality in cell-mediated immunity and ability of neutrophils to kill several types of microbes is commonly seen in iron-deficient patients. Legumes, grains and dry fruits   are rich sources of iron.

 Selenium (Se): Selenium is a trace element having critical functional, structural, and enzymatic roles, in a range of proteins. In addition to critical roles in many non-immune tissues within the body, selenium is needed for the progression of both natural and acquired immune system. Selenium is an important component of the body’s antioxidant system. It has been found that inadequate selenium status is linked to the increase incidence and severity of viral infections. The richest sources of selenium are cereals, grains, dairy products and Brazil nuts. Fruits and vegetables  provide low amounts of selenium.

 Zinc (Zn): Almost all cells in our body contain zinc, a vital nutrient for growth and development. Both zinc insufficiency as well as excess leads to changes in immune cell numbers and activities, which results in increased susceptibility to infections and development of inflammatory diseases. Interestingly, zinc has the ability to reduce oxidative stress which has been shown to help ward off disease. The best sources are   legumes, cheese, walnut, hazelnut and whole grains.

 Copper (Cu): Cu is essential for optimal innate immune function, and nutritional deficiency leads to increased susceptibility to infection. Copper-dependent enzymes provides natural defense against free radicals that damage the body. Interleukin 2 is reduced in copper deficiency and is likely the mechanism by which T cell proliferation is reduced. Additionally Cu deficiency also led to impaired neutrophil function. Sources   of copper   include whole grains, nuts, seeds, legumes   and spinach.

 PREBIOTICS AND PROBIOTICS: 

Nutrients may impact directly or indirectly upon immune cells causing changes in their function or may exert effects via changes in the gut microbiome. The gut is the largest immune organ in the body, accounting for 25% of the immune cells in the body that provide about 50% of the body’s immune response. Diet and antibiotic exposure changes the composition of gut microbiome. Probiotics and prebiotics are beneficial for the gut microbiome and strengthen the immune system by changing the expression of cytokines.

Probiotics are “living microorganisms” which exert a prophylactic and therapeutic effect by improving the internal microbial balance. Yogurt is one of the best sources of probiotics, which are friendly bacteria that can improve our health. 

Prebiotics are non-digestible substrate that is selectively utilized by the beneficial microbes conferring health benefits. Prebiotic fiber is a non-digestible part of foods like bananas, onions and garlic, the skin of apples, beans, and many others. It helps in the stimulation of immune system, which can be direct or indirect through increasing population of beneficial microbes or probiotics, especially lactic acid bacteria and Bifidobacterium, in the gut.  

IMMUNONUTRITION

Immunonutrients exert modulatory role on immune response and hence improve the immune function. Immunonutrients include Omega 3 fatty acids, arginine, glutamine, sulphur containing amino acids, and anti-oxidants.

Omega 3 fatty acids:  Omega 3 fatty acids have anti-inflammatory actions, which helps to reverse immunosuppression by down-regulating eicosanoid production. Vegetarian food sources include nuts especially walnuts, flax seeds, flax seed oil, leafy vegetables.

Arginine: Arginine is an essential nutrient for both innate and adaptive immune systems. It serves as a physiological substrate for enzymes, a building block for tissue proteins and a regulatory molecule in signal transduction pathways in cells (including immunocytes). It enhances lymphocytic progress and phagocytosis, and speeds up the wound healing. Hypoargininemia might increase susceptibility to infection.

Glutamine:  Glutamine is non-essential amino acid and provides an important energy source for many cells including immune cells. It also serves as a precursor for nucleotide synthesis, particularly relevant for rapidly dividing cells such as the immune cells during an immune response. In catabolic conditions (e.g., infection, inflammation, trauma), glutamine is released into the circulation, an essential process controlled by metabolic organs such as the liver, gut, and skeletal muscles. Despite this adaptation, a significant depletion of glutamine is seen in the plasma and tissues in critical illness, which has provided a rationale for the use of in clinical nutrition supplementation of critically ill patients.

Sulphur amino acids: They enhance antioxidant status by maintaining concentrations of glutathione, one of the key antioxidants in the body.

Anti-oxidants: They limit pathological aspects of the cytokine-mediated responses to infection and injury. Many of the antioxidants act in a complementary fashion in oxidation/reduction cycling. Micronutrients also influence antioxidant defence response since some of these trace elements are present in antioxidant enzymes: ceruloplasmin (copper), superoxide dismutases (copper, zinc, manganese), and glutathione peroxidase (selenium).

HERBAL PLANTS AS IMMUNOMODULATORS

Herbal immunomodulator is substance which stimulates or suppresses the components of immune system including both innate and adaptive immune responses. Many spices in the Indian kitchen are understood to have the immune boosting properties. 

Garlic: Garlic’s immune boosting properties seem to come from a heavy concentration of sulfur-containing compounds, such as allicin.

Ginger: Ginger is another immunobooster with anti–bacterial and anti-inflammatory properties which help in keeping several ailments at bay and helps fight infections.  

Turmeric: Turmeric, the Indian solid gold plays a vital role in spicing up the immune system. Most of the medicinal effects have been attributed to curcumin which acts as an efficient immunomodulator. Studies have shown that curcumin is active against different viruses, bacteria and fungi, including even highly pathogenic, emerging and multi-drug-resistant strains. 

Green tea: Both green and black tea are packed with flavonoids, a type of antioxidant. Green tea really excels is in its levels of epigallocatechin gallate (EGCG), another powerful antioxidant. In studies, EGCG has been shown to enhance immune function. 

HYDRATION 

Adequate hydration during viral illness helps speeding recovery by strengthening the immune system, lowering fever, promoting healthy cell signaling, moisturizing membranes and improving nutrient absorption. A normal person should aim to consume 2.5 – 3 litres of water per day. 

SLEEP

Sleep supports the proteins and cells of our immune system and strengthens our body's immune response. During any infection, getting enough sleep is of prime importance. It is essential to get 6-8 hours of good quality sleep. Maintaining the circadian rhythm is equally important.

EXERCISE

 Regular exercise is one of the pillars of healthy living. Just like a healthy diet, exercise can contribute to general good health and therefore to a healthy immune system. Regular exercise inhibits inflammatory cells aggregation and infiltration. It may contribute even more directly by promoting good circulation, which allows the cells and substances of the immune system to move through the body freely and do their job efficiently.

STRESS MANAGEMENT

Negative emotion is directly related with immune de regulation and production of inflammatory markers. Meditation, yoga, recreation, planning and time management is important to avoid stress and boost immunity. Yoga is one of the most effective and time-tested natural immunity boosters that can lead to a healthy body. Yoga helps to lower the stress hormones that compromise the immune system, while also conditioning the lungs and respiratory tract, stimulating the lymphatic system to oust toxins from the body, and bringing oxygenated blood to the various organs to ensure their optimal function. It is also important to undertake spiritual activities and live life of moderation.

CONCLUSION 

Nutritional modulation of the immune system has applications not only in clinical settings but also in healthy population, acting to reduce or delay the onset of immune mediated chronic diseases.

 Our first line of defense is to choose a healthy lifestyle. Following general good-health guidelines including hand wash and hygiene practices is the best step we can take toward naturally keeping our immune system strong and healthy.  Consuming a balanced diet provides all the necessary nutrition required but where there are challenges in meeting dietary recommendations, supplements may be incorporated in the diet.

As our beloved Swami says: 

 “As is the food, so is the mind; 

As is the mind, so are the thoughts

As are the thoughts, so is the conduct

As is the conduct, so is the health.”