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Disclaimer: the information provided in this article is not a substitute to searching medical advice.

While the principles of healthy eating are often presented in the context of preventing or improving non-communicable diseases, diet also plays a very important role for our ability to fight against infectious diseases.

Here are some key dietary considerations for this period of Covid-19 epidemic:

1. Optimal immune function is dependent on a healthy immune system.

2. Adequate nutrition is crucial to ensure a good supply of calories as well as macronutrients and micronutrients required for the development, maintenance and expression of the immune response.
An inadequate intake of micronutrients at any stage of life affects various functions within the immune system, manifesting in decreased resistance to infections and an increase in the severity of symptoms.1
In older people impaired immunity is often caused by multiple micronutrient efficiencies due to lack of appetite, under-eating, etc. An inadequate nutrition can also be related with a lack of food supplies as it can happen in times of financial restrictions, drought or through wars, disasters or poverty.

3. The nutritional status can also be compromised by poor diets characterized by energy-dense, micronutrient-poor convenience food like in some types of western diets. These diets tend to be rich in calories, refined sugars, salt, white flour, processed meats, animal fats and food additives while at the same time often lacking the fibers, vitamins, and minerals that are needed for an adequate immune response. “Western diets contain both direct triggers of inflammatory responses and induces indirect triggers that are produced via alterations in the gut microbiome”. A dysbalanced gut microbiome can cause disturbed barrier integrity and the induction of systemic inflammatory processes2,3.

4. Nutrients known to modulate the immune status if they are provided in sufficient amounts include: Vitamin A, B-carotene, folic acid, vitamins B6, B12, C, D and E as well as iron, zinc and selenium known to play a pivotal role in maintaining the antioxidant/oxidant balance in immune cells1.

Vitamin A: Is important for the normal functioning of innate immune cells (e.g., NK cells, macrophages, neutrophils), necessary for proper functioning of T and B lymphocytes, and thus for generation of antibody responses to antigen1.

Food sources of Vitamin A: Lacto-ovo vegetarian food sources of vitamin A are dairy and eggs. Plant sources of carotenoids that are converted into vitamin A by the human body are found in vegetables and fruits, such as: carrots, orang sweet potato, butternut squash, spinach, broccoli, kale, spring greens, romaine lettuce, beets, tomatoes, red and yellow peppers, cantaloupe, peas, and dried apricots. Some herbs and spices also contain beta-carotene: paprika, cilantro, parsley, marjoram, sage, coriander. Pairing these foods, herbs, and spices with a healthy fat such as olive oil, avocado or nuts and seeds can help their absorption4.

Vitamin B6: Play a role in lymphocyte proliferation, differentiation and maturation as well as antibody production1.

Food sources of Vitamin B6: Vitamin B6 is well distributed in foods and the gut microbiome produces relatively high amounts of absorbable vitamin B6. Plant sources are tofu, sweet potatoes, avocado, chickpea, potatoes, acorn squash, butternut squash, spinach, green pea, banana, plum, prunes, nuts (pistachio, chestnuts, hazelnuts, Brazil nuts, cashew nuts), elderberries, tomato juice and sauce, mango, pineapple, grapes.4,5

Vitamin B9 / folates: Maintains innate immunity, plays a role in cell-mediated immunity and is important for sufficient antibody response to antigens1

Food sources of Vitamin B9: Foods as leafy green vegetables, asparagus, legumes (bean, peas, lentils), beets, citrus fruits, Brussels sprouts, broccoli, wheat germ, nuts and seeds, papaya, banana, and avocado are sources of folate. Folate fortified foods such as wheat flour also contribute with intake of this vitamin in countries were fortification is mandatory. Lacto-ovo vegetarians may obtain folate from eggs as well.4,5

Vitamin B12: Facilitates the production of T lymphocytes1

Food of Vitamin B12:
While plant-based foods are typically not a source of vitamin B12, significant levels can be found in some fortified foods such as: fortified ready-to-eat breakfast cereals, fortified plant beverages (made from soy, rice, almond, coconut, oats, hazelnut, or cashew), fortified vegetarian meat analogs (canned and frozen), or fortified nutritional yeast . It is also available as a B12 supplement and as part of many multivitamin supplements. It is important to note that inactive analogs of vitamin B12 may be present in some foods such as spirulina, seaweed, and fermented foods such as tempeh.4,5,6,7,8 Lacto-ovo vegetarians may obtain their vitamin B12 supply from eggs and dairy products.6

Vitamin C: Stimulate the production, function and movement of leukocytes (e.g., neutrophils, lymphocytes, phagocytes, an increase serum levels of antibodies, has roles in lymphocyte differentiation and proliferation1,14
A low vitamin C status also increases susceptibility to infections such as pneumonia.1

Food sources of Vitamin C: Vitamin C is almost exclusively found in plant foods, mainly in fruits (e.g., acerola, cantaloupe, citrus fruits and juices, kiwifruit, mango, guava, papaya, pineapple, berries, watermelon) and vegetables (e.g., tomato, broccoli, cauliflower, potato, Brussels sprouts). Its concentration is affected by a number of factors such as: season of the year, fruit ripening stage, cooking process, storage time etc.4

Vitamin D: Increases antimicrobial activity of macrophages and monocytes, upregulate the phagocytic activity of innate immune cells. Interacts with both the innate and adaptative immune cells.

Sources of Vitamin D: Sunlight: ultraviolet light striking the epidermis catalyzes the synthesis of Vitamin D. Foods: egg yolks, some mushrooms, foods fortified with vitamin D such as orange juice, soy milk, and cereals.

Vitamin E: Enhances T cell-mediated functions and lymphocyte proliferation1

Food sources of Vitamin E: Vegetarian foods with higher amounts of vitamin E are vegetable oils (e.g., wheat germ oil), seeds (sunflower), nuts (almonds, hazelnuts, pine nuts, peanuts, Brazil nuts), avocado, mango, kiwi, and whole grains.4

Iron: Is involved in the regulation of cytokine production and action and is important in the generation of reactive oxygen species that kill pathogens1

Food sources of Iron: A well-planned plant-based diet can provide ample iron to match requirements for absorbed iron. In order to optimize iron intake and decrease the risk for low iron stores in the body it is important to assure good food sources and enhance its absorption.

Vegetarian sources:
• Legumes, whole grains (prefer non-refined/whole foods), low-oxalate green vegetables (broccoli, kale, collards, Chinese cabbage, okra, and bok choy), sesame seeds, dried fruits (prunes, raisins, apricots), pistachios, hazel nuts, almonds, cane molasses
• Iron fortified vegetarian foods (cereals, beverages, etc) can increase intake.
To increase/optimize bioavailability:
• Reduce inhibitors and increase enhancers of iron absorption in concomitance with your main meals:
o Avoid dairy products and polyphenol- and tannin-rich foods and beverages such as black tea, some herb teas (peppermint, chamomile, vervein, lime flower, pennyroyal), coffee, and cocoa.
o Prefer vitamin-C food or drink sources: citrus fruits, juices, vegetables (e.g., tomato with lime in a salad), fresh produce (e.g., papaya).
o Avoid adding wheat bran to your diet if it is already rich in whole grains and legumes.
o Avoid indiscriminate use of anti-acid
o Avoid alcohol consumption. Alcohol increases iron absorption and it may predispose to iron accumulation in the organism (hemochromatosis).
• Use fermented foods (e.g., low sodium soy sauce, sourdough bread).
• Use cast-iron or steel cookware to prepare acidic items, such as tomato or sweet-and-sour sauce.4,7,8,9

Zinc: Has a central role in cellular growth and differentiation of immune cells that have a rapid differentiation and turnover. 1,10,11
Zinc deficiency can increase thymic atrophy, decrease lymphocyte number and activity, and increase oxidative stress and inflammation by altering cytokine production. As a result, the risk of all types of infection (bacterial, viral, and fungal), including pneumonia, is increased.

Food sources of Zinc: Plant sources: whole grains (prefer non-refined/whole foods), wheat germ, sprouted seeds and legumes, tofu, tempeh, miso, legumes, nuts, and seeds. Lacto-ovo vegetarians: eggs and dairy. Zinc fortified cereals and meat analogues (veggie meats) can increase intake.
To increase/optimize bioavailability: consume yeasted breads, sprouts, roasted or soaked nuts, and presoaked legumes. Avoid adding wheat bran to your diet if it is already rich in whole grains and legumes.4,7,8,9
Selenium: Selenoproteins are important for the antioxidant host defense system affecting leukocyte and NK cell function, Involved in T lymphocyte proliferation1

Food sources of Selenium: Brazil nut is the richest selenium source known to date. Other vegetarian sources are mushrooms, alfalfa, nutritional yeast, whole grains, and cruciferous vegetables (e.g. mustard greens, cabbage, broccoli, cauliflower).4,8

5. Excessive intake of sugar and refined grains can cause immune-metabolic disturbances in our body. A high sugar diet promotes weight gain, intestinal dysbiosis and gut inflammation. It is better to enjoy sweets from whole, fresh or dried fruits.1,10

6. A balanced plant based diet
Here after a science-based graphic representation of a plant-based food guide in pyramid shape developed by researchers from the Loma Linda University.
Nine food groups are making up the two most common vegetarian traditions: lacto-ovo and vegan.
The five major plant-based food groups - whole grains, legumes, vegetables, fruits, and nuts and seeds - form the vegan trapezoid in the lower part of the pyramid.
At the top are four optional food groups -vegetable oils, dairy products, eggs, and sweets - that may be added to the core plant food groups to meet the need for dietary guidance of lacto-ovo vegetarians.
The graphic also presents the importance of vitamin B12 supplementation for individuals consuming a strict vegan dietary pattern.
Other important lifestyle factors include frequent exposure to sunlight, regular physical activity, and the abundant consumption of water and fluids. These positive dietary and lifestyle factors synergistically contribute to improve our general health and enhance our ability to fight against infectious diseases.13


7. Infections and supplements
In light of their positive effects on respiratory tract infections, it has been suggested that there is a good rationale to combine vitamins C and D with zinc to support immune functions and help minimize the risk or severity of infections12

Vitamin C supplementation & infections
- Critically ill patients can exhibit decreased vitamin C plasma levels15
- There is emerging literature suggesting that vitamin C may play an adjunctive role in the treatment of a variety of viral infections.14
- In addition to demonstrating activity against influenza and herpes virus, vitamin C has been reported to have activity against a number of other viruses 14
- Several clinical trials in hospitals suggest the beneficial effects of vitamin C supplementation in patients with sepsis.14,15

Zinc supplementation & infections
- Low zinc is associated with an impaired immune system and poor prognosis in conditions such as sepsis 16
- Zinc administered in a prophylactic manner as prevention for respiratory infections has been showing some positive results specially for children16
- During an infection, the decision to administer zinc must take into account the risks of creating a zinc microenvironment that is more favorable for pathogen growth, meanwhile downgrading the efforts carried out by the innate system to reduce free zinc.16
- There is a need for more research to investigate and understand the therapeutic potentials of zinc for infectious diseases. Some trials are currently being done regarding Covid-19.

Vitamin D supplementation & Infections
- Because vitamin D is produced in our skin under sunlight exposure, maintaining adequate levels of this vitamin may be challenging, especially with recommendations of social distancing and longer periods staying indoors.
- Evidence from scientific studies show that vitamin D supplementation can protect against acute respiratory tract infections, including the seasonal and pandemic flu caused by H1N1 virus.17
- Doses greater than 1000 IU were tested and showed to be beneficial in individuals across all ages, with pre-existing chronic illnesses, and with vitamin D deficiency.18,19
- Although there is no current evidence whether vitamin D supplementation will reduce the severity of COVID-19, experts are considering target doses of 1000 or 2000 IU as a reasonable option, especially for those with low levels of this vitamin.20

Elderly & Supplementation
Micronutrient deficiencies are common in older people. An insufficient intake of micronutrients in older people has been reported both in the community (vitamins A, B12, D and zinc) and at a higher prevalence in long-term care facilities (vitamins A, D, and E), while lower food intake has been associated with lower intakes of calcium, iron, zinc, B vitamins and vitamin E in older people 1
Interestingly the high-risk group for the present Covid-19 pandemic is also a group particularly affected by the deficiency of micronutrients that are critical for a good immune response.
Supplementation with a complex micronutrient formulation in older people increased the number of various types of immune cells, including total lymphocytes, and induced a shift from memory T cells to naïve T cells.1

Marcia Cristina Teixeira Martins, PhD, MSc, RD, RPh
Valérie Dufour, MPH, RD