Table 1.

Micronutrients: food sources, immune system functions and recommendations

Micronutrient	Food sources [131]	Functions	Recommendation (RDA)—adults (18–70 years)	Quantity of micronutrients per 100 g of food [143, 144]
Copper	Liver, oysters, whole grains, oilseeds and chocolate	Intracellular antioxidant [64] Contributes to the inflammatory response [34] Acts on cell differentiation and proliferation [34] Assists in the NK cells activity [145] Involved in the antibodies Productions of antibodies and cellular immunity [28]	900 µg/day for both men and women	Brazilian nut—1.7 mg Chocolate 2.2 mg Cooked bovine liver—9.9 mg Cooked oysters—2 mg Hazelnut—1.5 mg Oat bran—0.4 mg
Iron	Meat, liver, legumes, seafood, dark green vegetables	Contributes to free radicals formation to react against viruses and bacteria [146] Participates in the T lymphocyte proliferation and differentiation [146] Participates in the enzymatic action against pathogens [147]	8 mg/day for men and 18 mg/day for women	Cooked beef—2.6 mg Cooked black beans—1.67 mg Cooked bovine liver—6.3 mg Cooked broccoli—0.8 mg Cooked chicken leg—2.1 mg Cooked green peas—1.63 mg Cooked pork—1.2 mg Cooked spinach—1.5 mg Steamed seafood—22 mg
Magnesium	Cereals and seeds, green leafy vegetables, seafood and oilseeds	Magnesium supplementation is correlated to improve lung function [148]	420 mg/day for men and 320 mg/day for women	Almonds—305.1 mg Cooked green beans—151 mg Cooked oysters—39 mg Cooked shrimp—34 mg Cooked spinach—68.4 mg Hazelnut—282.3 mg Pumpkin seed—532 mg Sesame—340.4 mg Sunflower seed—121 mg Wheat germ—321.4 mg
Selênium	Oilseeds, seafood and cereals	Essential for several enzymes involved in the redox balance [149] Increases T cells proliferation [149] Increases the Natural Killer cells activity [149] Improves the antiviral vaccine responses (including influenza vaccine) [149] Improves antiviral immunity [149] Decreases virulence of some influenza strains and other viruses [150]	55 µg/day for both men and women	Brazilian nut—126 µg Brown rice—2.7 µg Canned sardine in oil—46 µg Tuna—52.5 µg Whole wheat flour—13.6 µg
Vitamin A	Liver, fish liver oil, egg yolk, butter, green leafy vegetables, yellow-orange vegetables and fruits	Action in resistance to infections [151] Maintenance of the lymphocyte pool and T lymphocyte synthesis [151] Maintenance of epithelial cell differentiation and immune competence [151] Improves neutrophils, macrophages and Natural Killer cells functions [151] Role in the T lymphocytes differentiation [151] Role of prevention and treatment of respiratory tract infections [152]	900 µg/day for men and e 700 µg/day for women	Broccoli—279 µg Butter—1013 µg Carrot—1326 µg Cod liver oil—30,000 µg Cooked bovine liver—14,574 µg Egg yolk—148 µg kale—496 µg Manga—787 µg Spinach—484 µg
Vitamin B12	Meat, liver, fish, eggs, milk and dairy products	Immunomodulator [28] Acts on the NK cells functions [34] Assists in the T lymphocytes productions [34] Contributes indirectly to the antibodies' production and its metabolism [34]	2.4 µg/day for both men and women	Boiled egg—1 µg Cooked beef—2.5 µg Cooked bovine liver—112 µg Cooked chicken—0.36 µg Cooked salmon—2.8 µg Cooked trout—5 µg Cooked tuna—1.8 µg Cottage cheese—2.81 µg Steamed seafood—99 µg Whole milk—0.33 µg
Vitamin B6	Meat, bananas, broccoli, carrots, spinach and oilseeds	Helps in the inflammatory process regulation [34] Participates in the amino acids, cytokines and antibodies synthesis [34, 145] acts on the lymphocytes proliferation, differentiation, and maturation [145] Assists in NK cells activity [34]	Men 18–50 years: 1.3 mg/day 51–70 years : 1.7 mg/day Women 18–50 years : 1.3 mg/day 50–70 years : 1.5 mg/day	Banana—0.6 mg Bovine liver—1.43 mg Brazilian nuts—0.26 mg Carrot—0.23 mg Cooked beef—0.40 mg Cooked chicken—0.63 mg Hazelnut—0.6 mg Nuts—0.56 mg Spinach—0.15 mg
Vitamin B7	Seeds, oilseeds, eggs, soy protein, salmon, carrots and sweet potatoes	Important function in NK cells activity [42] Contributes to the generation of T lymphocytes [42] Important in the maturation and responsiveness of immune cells [42]	30 µg/day for both men and women	Boiled egg – 16.5 µg Carrot – 5 µg Cooked salmon – 5 µg Hazelnut – 75 µg Peanut – 101.4 µg Sweet potato—4.3 µg Wheat bran – 44.4 µg
Vitamin B9	Meat, bananas, broccoli, carrots, spinach and oilseeds	Contributes to the innate immunity maintenance [48] Contributes to the antibody response to antigen [34] Contributes to the T cells proliferation [34]	400 µg/day for both men and women	Boiled egg—40 µg Chicken liver—770 µg Cooked beans—149 µg Cooked bovine liver—220 µg Cooked white rice—60.7 µg Lentil—180 µg Pea—65 µg Spinach—108 µg Wheat germ—357 µg
Vitamin C	Citrus fruits, acerola, pineapple, strawberry, melon, tomato, pepper, broccoli and cabbage	Positive modulation of the aging process and immunosenescence [153] Positive modulation of the low-grade inflammatory process [153] Improves phagocyte motility and chemotaxis [50] Improves antibody levels, differentiation, and proliferation [50] Modulates positively production of inflammatory cytokines [50] Role in the prevention and treatment of respiratory infections [50] Decreases the pathogenicity of viruses, bacteria, parasites and fungi [154]	90 mg/day for men and 75 mg/day for women	Acerola—941.4 mg Broccoli—34.3 mg Cashew—219.3 mg Green Bell pepper—100.2 mg Kale—96.7 mg lemon—38.2 mg orange—53.7 mg Papaya—82.2 mg Passion fruit—19.8 mg Pineapple—34.6 mg Strawberry—63.6 mg Tomato—21.2 mg Yellow Bell pepper—201.4 mg
Vitamin D	Fish liver oil, milk and dairy Products, butter, eggs, fat cheeses	Stimulates the innate immune response in bronchial epithelial cells [155] Stimulates the monocytes to macrophages differentiation [155] Stimulates antibacterial protein synthesis [155] Stimulates the mechanisms associated with the pathogens elimination [155] Supplementation seems to have a protective effect in respiratory tract diseases (mainly in individuals with hypovitaminosis D) [156] Individuals with hypovitaminosis are more susceptible to respiratory tract infections [157]	15 µg/day for both men and women	Boiled egg—13 µg Butter—1.54 µg Cheddar cheese—0.32 µg Cod liver oil—252 µg Fortified milk—1 µg
Vitamin E	Vegetable oils, wheat germ, egg, dark green vegetables, nuts and almonds	Membrane antioxidant—cell protection [158] Stimulates lymphocyte proliferation [158] Supplementation associated with antibacterial effects [158] Increases the activity of NK cells [158] It seems to have a protective effect against pneumonia and colds [137]	15 mg/ day for both men and women	Almond –5.5 mg Broccoli—1.05 mg Cabbage—0.61 mg Canola oil—21.3 mg Corn oil—21.3 mg Egg—1 mg Nuts –2.6 mg Peanut—7 mg Spinach—0.95 mg Sunflower oil—51.5 mg Wheat germ—19.1 mg
Zinc	Meat, seafood, oilseeds, whole grains and fortified grains	Function in the immune cells maturation and differentiation [159] Zinc deficiency is related to impaired innate immunity [159] Increases the Natural Killer cells activity and number [159] Regulation of inflammatory cytokines [160]) Participation in anti-inflammatory pathways [160]	11 mg/day for men and 8 mg/day for women	Boiled flank—8 mg Cashew nuts—4.7 mg Cooked brown rice—0.7 mg Cooked oyster—39 mg Grilled fillet—5.1 mg Popcorn—2 mg Roasted Tiger fish 2.1 mg Rolled oats—2.6 mg Wholemeal bread—1.6 mg