The role of nutrition

Nutrition plays a key role in maintaining a healthy lifestyle, but more importantly, healthy eating helps protect the immune system from toxins and infections. 

Our immune system is closely linked to the gut microbiota, which refers to the microorganisms that populate our digestive system and perform beneficial functions. 

Therefore, the quality of the nutrients we introduce with food plays a critical role in the efficiency of our immune system. 

Vitamin C

Vitamin C is an essential vitamin for humans, which means that our body is unable to produce it on its own but must obtain it from outside with food. It helps prevent infections and decreases their duration when they have already occurred.

Vitamin C is easily oxidized and lost by cooking at high temperatures, so it is best to steam vegetables and consume fruits immediately after removing them from the refrigerator or juicing them.

The foods richest in vitamin C, in addition to citrus fruits, are currants, kiwifruit, strawberries, and peppers, parsley, broccoli, arugula, Brussels sprouts, collard greens, lettuce, cauliflower, spinach, and kale.

The daily requirement for vitamin C is 105 mg for adult men and 85 mg for adult women, a quota that needs to be increased in pregnant and lactating women.

Vitamin E

Like vitamin C, vitamin E can strengthen the immune system due to its antioxidant capacity.

The daily requirement for vitamin E is around 8 mg, corresponding to 4 tablespoons of olive oil or 2 large servings of broccoli. 

Vitamin E is mainly found in vegetable oils (wheat germ oil, olive oil), nuts (almonds, walnuts, hazelnuts), and green leafy vegetables, such as spinach and broccoli.

Vitamin A

Although well-known for its essential function in vision health, vitamin A, or retinol, is also an excellent ally against infections as it maintains the integrity of the skin and mucous membranes, the first barrier to external pathogens.

It can be found in various plant and animal foods: cod liver oil and terrestrial animal liver, egg yolk, salmon and fresh tuna, eel, yellow-orange fruits and vegetables, and milk and dairy products.

Daily requirements for vitamin A, or retinol, range from 0.6-0.7 mg, which may increase to 0.95 mg during lactation.

Vitamin D

Known as the sunshine vitamin, it is one of the most important and powerful nutrients for supporting the immune system, partly because it helps the body absorb calcium.

Vitamin D is contained in appreciable amounts in only a few foods of animal origin and of low consumption because they are very fatty: cod liver oil, fatty fish such as canned salmon, herring, sardines, mackerel, tuna, eel, pork liver, butter, fatty cheeses, and whole chicken eggs.

For this reason, the best source of vitamin D remains sun exposure, which in most people ensures that their needs are met. Only when deemed necessary by the physician, can vitamin D be taken with a supplement.

The average vitamin D requirement is 400 international daily units without risk factors. Intakes may vary to 1,000 units per day due to risk factors or deficiency.

Vitamin B9 (Folic acid)

Vitamin B9 is essential for protein and DNA synthesis, as well as the formation of hemoglobin. Its proper presence in the body also helps prevent many cardiovascular risks and contributes to the immune system’s health.

It can be found in a variety of foods, both animal and plant-based, such as liver, kidney, brewer’s yeast, breakfast cereals, whole grain bread and pasta, asparagus, broccoli, artichokes, spinach, fresh legumes, oranges, kiwi, and strawberries.

The daily requirement for vitamin B9, or folic acid, is about 0.4 mg. However, mothers-to-be need to take 0.6 mg during pregnancy since the fetus uses maternal reserves of folic acid.


Iron helps the body transport oxygen to cells and plays a decisive role in many immune system processes.

It is available in several forms: heme iron, which is bound to the hemoglobin and myoglobin of animal products and easily absorbed by our bodies, and non-heme iron, from plant-based foods, eggs, and dairy products, which is more difficult to absorb.

Therefore, animal-based foods particularly rich in bioavailable iron include offal, red meat, and fish. Plant-based foods rich in iron – but poorly bioavailable – include dried legumes, dried and oily fruits, whole grains, and leafy vegetables.

Daily iron requirements vary according to age, sex, and special conditions such as pregnancy and lactation. On average, an adult man should take 10 mg/day of iron, while an adult woman should take 18 mg daily during childbearing and 10 mg daily after menopause.


Selenium is an excellent cellular antioxidant and appears to have a powerful effect on the immune system in preventing infection.

Animal-based foods such as meat, fish, and offal are the best sources, but some plant-based foods, such as nuts, particularly Brazil nuts, also contain appreciable amounts.

Adequate selenium intake varies with age and is about 20 micrograms per day up to age 3, 25 micrograms from ages 4 to 6, 35 micrograms from ages 7 to 10, 50 micrograms from ages 11 to 14, and 55 micrograms per day from age 15. In pregnant and lactating women, it rises to 60 and 70 micrograms per day, respectively.


Zinc is a trace element necessary for producing new immune system cells.

It is found mainly in animal-based foods such as meat (chicken, turkey, adult beef, lamb, rabbit), fish (anchovy, squid, octopus, sardine, cuttlefish), and dairy products (grana, parmesan, provolone). It can also be found in plant-based foods such as dried legumes, nuts, dried fruits, and cereals (corn, millet, parboiled rice).

The recommended population intake of zinc varies with age and is 9 mg per day for adult women and 12 mg per day for adult men.