Feeding your body certain foods can strengthen your immune system, decrease the severity of symptoms, and shorten the duration of an infectious disease.

Okay. Let’s get the bad news out of the way- When looking for ways to prevent infectious diseases like COVID, there’s no magic pill or single food or supplement that is guaranteed to boost your immune system or protect you against any virus. Now for the good news: You can make nutrition a priority and help your immune system stay healthy by eating a variety of healthy foods. So, your next step should be buying the right groceries. You can easily secure a nice variety of healthy options, even with a limited budget, by choosing shelf-stable foods like canned goods, pasta, rice, and legumes; selecting some frozen foods like fruits and vegetables; and utilizing your freezer to store bread, meats, vegetables, and fruits. Nutrition can help boost your immune system with high nutrient-density foods. Let’s begin by filling your plate with “immune-boosting nutrients.” One of the best ways to stay healthy is to eat healthy foods. Our immune system relies on a continual supply of nutrients to work at its higher level. Some of the key nutrients that play a role in immunity are vitamins and minerals with antioxidant abilities, phytochemicals (a non-nutrient substance from plants with health benefits), proteins, and water. Here are some key nutrients and their foods sources that play an essential role in your immune system and health:

VITAMIN C is an antioxidant that protects cells from oxidation, increases levels of antibodies in the blood, and may reduce the duration of colds. The best way to consume this vitamin is by eating a combination of fruits such as blueberries, strawberries, blackberries, cherries, mangoes, pineapples, oranges, grapefruit, kiwis, lemons, tangerines, clementine, tomatoes, and fresh vegetables like kale, cauliflower, broccoli, spinach, cabbage, brussels sprouts, and red and green peppers. Eating them raw is preferred since heat can destroy some of the vitamin C. However, many of these can be purchased frozen; frozen produce maintains its nutritional value well. They can also be bought and consumed fresh, then stored in your freezer to be used later for smoothies or soups.

Vitamin C is water-soluble, which means that the excess supplementation (over 2,000 mg/day) will be eliminated in your urine. If you take a vitamin C supplement, buy one with 200-500mg and take it 2 to 3 times a day in morning-midday-night intervals. It is a good strategy to maximize its absorption and battle infectious diseases.

VITAMIN D has essential functions beyond calcium and bone health, including helping our immune systems stay strong during the cold and flu season. Vitamin D alters the activity and number of white blood cells (T2 killer lymphocytes), reducing the spread of bacteria and viruses. The deficiency of this vitamin is associated with increased susceptibility to infection. Cod liver oil, a rich source of vitamin D, was employed as a treatment for tuberculosis and overall increased protection from infections many years ago before any scientific proof of its beneficial effects was available. Recent studies from the National Institute of Health warn that low vitamin D levels are associated with frequent colds and influenza.

Good food sources of vitamin D include fatty fish like sardines, salmon, mackerel (canned or fresh); egg yolks, fortified milk, and plant milk products (almond milk); cheese, fortified cereal, and juice; tofu, mushrooms and, of course, sunlight (20min/day). Even though there is no evidence that vitamin D supplements will protect you from COVID-19, it’s wise to consider them if you feel you are not getting enough of this vital vitamin through your diet. Also, choose supplements containing D3 (cholecalciferol) since it’s better to raise your vitamin D blood levels.

BETA-CAROTENE has antioxidant properties that help neutralize free radicals and is a precursor of Vitamin A and the primary safe dietary source for it. Vitamin A is essential for normal growth and vision and vital for a robust immune system. In addition, many studies suggested that beta-carotene may enhance cell-mediated immune responses, particularly in the elderly, by helping antibodies respond to toxins and foreign substances.

Good beta-carotene sources include sweet potato, carrot, mango, apricot, dark leafy greens like spinach and kale, broccoli, butternut squash, romaine lettuce, and cantaloupe. While eating a lot of Beta-Carotene in foods is considered harmless, supplementations of either beta-carotene or vitamin A is not recommended because it can suppress the immune system and cause toxic reactions in your body.


ZINC oral formulations, in combination with vitamin C, may shorten the duration of symptoms of the common cold and help cells in your immune system grow and differentiate properly, according to studies. Although the amount of zinc a person needs can change on a case-by-case basis, on average, an adult man needs 11 milligrams of zinc per day. This amount is naturally found in different foods and is also available as a dietary supplement. But beware! Excessive intake of this trace mineral by supplementation can interfere with absorbing other essential nutrients like Iron and inhibit immune system function.

Good food sources of zinc include oysters (fresh or canned), crab, lobster, shrimp, lean beef steak and pork chop, dark poultry meat, yogurt, fortified cereals, specific nuts (pine nuts, peanuts, cashews, and almonds), specific seeds (hemp, pumpkin, squash, and sesame seeds), wheat germ, chickpeas, lentils, and tofu.

PROTEIN is a crucial building block for immune cells and antibodies and is primarily responsible for helping the immune system work at its best. That is why a small portion of protein is essential in each meal and snack every day.
Protein comes from animal and plant-based sources, including fish, poultry, beef, milk, yogurt, eggs, cottage cheese, nuts, seeds, beans, legumes, and lentils.

PREBIOTICS & PROBIOTICS help boost the health of the microbiome in your gut, where 70% of your immune system resides and, in turn, supports your immune system. Prebiotics are the dietary fiber that acts as a fertilizer for the good bacteria in your gut. Plants provide plenty of fiber, which helps feed the good bacteria and regularly flush your gastrointestinal (GI) tract of harmful bacteria looking to gain a foothold. Probiotics are live bacteria found in yogurt and other fermented foods. To be active and useful, they must be kept alive by controlling the temperature (refrigeration) and proper environment (avoid heat, stomach acid, and long shelf time).

Sources of probiotics include dairy foods such as yogurt, kefir, buttermilk, cottage cheese, and fermented foods such as kombucha, kimchi, sauerkraut, miso, tempeh, and sourdough bread. Sources of prebiotics include asparagus, whole grains, banana, onion, garlic, leeks, artichoke, legumes, and beans.

WATER is the most indispensable nutrient. About 60% of our body is water, incorporated into the cells, tissues, and organs. Water is needed for many chemical reactions as a solvent and is the body-cleansing agent. Drinking enough water every day is good for overall health; it can prevent dehydration, a condition that can cause unclear thinking, mood change, body overheat, constipation, and kidney stones, but how much is enough? The need for water is influenced by many factors such as body size, age, gender, alcohol consumption, cold or hot weather, heated environment, intake of protein, salt or sugar, and physical activities.

My grandmother always told me to drink 8 cups of water a day; was she right? Yes, because plain drinking water is one best way of getting fluids as it has zero calories. No, because the experts recommend about 12 to 15 cups of fluids a day. But, daily fluid intake (total water) is defined as the amount of water consumed from foods, plain drinking water, and other beverages like juices, milk, soda, or tea. On average, 20 percent of your water intake is from the foods you eat. Some solid foods like fruits and vegetables are surprisingly high in water, such as broccoli, cucumber, celery, strawberries, lettuce, and tomatoes, and they count as part of your water intake.
Remember that variety and balance are essential to following a nutritious diet. Eating just one of these foods won’t be enough to help you fight off the COVID or any other infectious disease, even if you eat it constantly. Instead, eat a variety of fresh or frozen fruits and vegetables every day and pay attention to serving sizes (at least 2 to 4 cups/day). If taking supplements, it is better to take a multivitamin with minerals once or twice a day with your morning and evening meals to avoid getting too much of a single vitamin and too little of others. Avoid eating junk and processed foods high in fat and sugar like chips and desserts and big portions of red meat and refined grains. They may weaken your immune system and make you susceptible to infectious diseases or other health problems. Your body works hard to keep you healthy and active, so make sure you do your part by giving it the foods needed to stay strong


Seizer, F., & Whitney, E. 2019. Nutrition: Concepts and Controversies 15th Ed. Belmont, CA: Cengage Learning.

Center of Disease Control-CDC. 12/2020. Get the Facts: Drinking Water and Intake. https://www.cdc.gov/nutrition/data-statistics/plain-water-the-healthier-choice.html

US Department of Health and Human Services, National Center for Complementary and Integrative Health. 3/2020. Probiotics: What You Need to Know. https://nccih.nih.gov/health/probiotics/introduction.htm#hed1

Omeed Sizar; Swapnil Khare; Amandeep Goyal; Amy Givler. 7/2021. Vitamin D Deficiency. Treasure Island (FL): StatPearls Publishing: https://www.ncbi.nlm.nih.gov/books/NBK532266/


Iris Mercado

Dr. Iris Mercado is a Tenured Associate Professor from the Education Department, Health Education Unit. She holds an EdD in Health Education, MS in Public Health and Nutrition, BA in Nutrition and Dietetics, certificates in Weight Control Management and Sports Nutrition. She is a member of the Academy of Nutrition and Dietetics. With over 30 years of working as a health educator and nutritionist/dietitian, Dr. Mercado belief that people can change behaviours and adopt healthy lifestyles with the appropriate support and motivation.


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