Dr. Francesco Milano , expert in Nutrition , illustrates the importance of diet in maintaining the balance of the microbiota and how this can influence and support the immune system. Particular light is placed on two important vitamins, vitamin C and vitamin D , which have long been known for their action to support the defenses.

"We live in a world full of microorganisms and we have evolved to learn to live with them in harmony. Some are fundamental for our health, so much so that we host them in numerous areas of our body: we have microorganisms on our skin, in the oral cavity, in the upper and lower respiratory tract and intestines, just to name a few. Taken together they constitute the so-called microbiota and, thanks to their nature and function, when the system is in equilibrium they provide a defense against pathogenic bacteria, viruses and yeasts.

A fundamental aspect of maintaining this delicate balance is represented by the diet . An adequate and balanced diet represents the pillar to maintain and support an efficient immune system , in order to prevent infections and chronic-degenerative diseases. "

- What are the nutrients whose deficiency can most affect our defense system?

"Just by way of example, it is well known that a low protein intake in the diet can increase the risk of infections because it is related, for example, to a low production of antibodies.

The nutritional status is also important to modulate the inflammatory and oxidative stress processes that support the immune response, but which must be finely regulated. In addition to protein intake, other protective nutritional factors are represented by essential fatty acids, especially of the Omega-3 series, fiber , vitamins A, B, C, D and E and minerals such as zinc, iron, selenium, copper and magnesium. "

- Among these, which are the most important, especially in this season?

" Vitamin D , which is a fat-soluble vitamin, ie soluble in fats, which is stored mainly in the liver. It is mostly produced by our body following the absorption of the sun's rays by the skin. This vitamin is a regulator of metabolism of calcium which helps to maintain normal levels of calcium and phosphorus in the blood; for this reason it is useful in calcifying bones . "

- Are there recent studies on the role of vitamin D in support of its preventive and defensive action?

"Recent research also highlights an extra-skeletal role, since its receptors are distributed in numerous cells of the body. Among the main actions that are being investigated, there are its role in the modulation of the immune system , in the prevention of tumor pathologies. and in fertility .

The work of Professor Jun Sun of the University of Illinois at Chicago, who investigated the modification of the composition of the intestinal microbiota following vitamin D supplementation, is interesting. This could pave the way for further interesting investigations about its immunomodulatory action, which it could also be mediated by direct action on the intestinal microbiota and airways. "

- There has always been talk, and we hear more and more, even of vitamin C.

" Vitamin C is a water-soluble essential nutrient that cannot be synthesized by humans.

A severe deficiency of vitamin C, which has highlighted its importance in prevention, causes scurvy, for example. Scurvy is characterized by the weakening of collagen -containing structures, resulting in poor wound healing and reduced immunity. Individuals with scurvy are highly susceptible to life-threatening infections, such as pneumonia. "

"In turn, infections can have a significant impact on vitamin C levels due to increased inflammation and metabolic requirements. Scurvy was noted at first that often followed infectious outbreaks in populations and cases of scurvy as a result of respiratory infection. This is especially evident for individuals who are already malnourished. "

- What would be the recommended daily intake of vitamin C?

"Although the amount of vitamin C required to prevent scurvy is relatively low (ie, ~ 10 mg / day), the recommended dietary intakes of vitamin C are up to a hundred times that of many other vitamins."

"Due to the body's low storage capacity for the water-soluble vitamin, regular and adequate intake is in fact required to prevent hypovitaminosis C. Epidemiological studies have indicated that hypovitaminosis C is relatively common in Western populations and deficiency. Vitamin C is the fourth major nutrient deficiency in the United States.

There are several reasons why vitamin C dietary recommendations are not being met, even in countries where food availability and supply should be sufficient. These include poor eating habits, life stages and / or lifestyles that limit intake or increase need for micronutrients (eg, smoking and alcohol or drug abuse), medical conditions, and exposure to pollutants. Even otherwise "healthy" individuals in industrialized countries may be at risk from lifestyle factors, such as those on an unbalanced diet and experiencing periods of excessive physical or psychological stress. "

- How can vitamin C help the body?

Vitamin C has a large number of activities, including immunomodulatory effects . It is a highly effective antioxidant , thus protecting important biomolecules (proteins, lipids, carbohydrates and nucleic acids) from damage due to free radicals and exposure to toxins and pollutants (eg cigarette smoke).

- Are there other compounds with a protective action that can be taken with the diet?

"Other protective factors concern phytochemical compounds contained in plants , such as polyphenols contained in green tea, fruit and vegetables or carotenoids, colored pigments that give fruit and vegetables their yellow, orange or red color, of which the best known is the beta-carotene.

All of these compounds act at various levels and in synergy to support the body's natural defenses. "

But what sources can we draw from?

The table shows the major food sources:


Beef, chicken, egg whites, dairy, potatoes, quinoa and soy

Lipids (rich in omega-3s)

Chia seeds, edamame, avocado, salmon, tuna and oats

Carbohydrates (fiber)

Chia seeds, whole grains, wholemeal bread, legumes, fruit and vegetables

Vitamin A

Carrots, cantaloupe, mango, salmon and eggs

Vitamin D

Mushrooms, salmon, chicken, eggs and low-fat yogurt

Vitamin E

Sunflower seeds, nuts, blueberries, kiwi and broccoli

C vitamin

Citrus fruits, broccoli, cauliflower and Brussels sprouts

Vitamin B6

Peanuts, lentils, tuna and shellfish

Vitamin B12

Shellfish, white yogurt and chicken breast


Pumpkin seeds, walnuts, soybeans, beef, lamb and shellfish


Dehydrated apricots. Cherry tomatoes, peas, shellfish, eggs and meat


Cashews, Tofu, Mushrooms, Beef, Oysters, Sweet Potatoes, and Quinoa


Sunflower seeds, coconut, salmon shellfish and turkey ham


Bran, dark chocolate, almonds, cashews, cocoa and peanuts


Orange, grapefruit, blueberries, strawberries, green and black tea, apple


Tomato, mandarin, spinach, cabbage and cantaloupe

"Maintaining a varied diet and an active lifestyle allows us to cope with various nutritional needs, preferring seasonal foods and cooking methods that preserve nutritional value ."

- For example?

"For example, it is better to skip the vegetables in a pan rather than boiling them in water: if you need to prepare boiled vegetables, I recommend not using too much water and keeping the cooking liquid to use it as vegetable broth, thus taking in vitamins and minerals that otherwise would be lost. "

- When is it appropriate to integrate micronutrients?

"When, due to increased needs or in particular situations, they cannot be satisfied with the diet, but pay attention to do-it-yourself: studies show that people who choose supplements themselves often integrate what they do not need and this, to the on the contrary, it can lead to imbalances with relative deficiencies. "