Foods You Should Eat To Give Your Immune System A Boost

You may think of your immune system as if it's a single part of your body, but it really is as the name implies: a system of many different cells and tissues working together and relying on dozens of nutrients to function properly.

There are two branches of the immune system: innate and adaptive. As the name "innate" implies, we're born with this form of immunity, a general first line of defense. The innate immune system encompasses the skin, mucus membranes, beneficial gut bacteria, and several types of white blood cells, including natural killer cells. The innate immune system works to physically or chemically block germs from entering the body. It also governs the inflammatory response when body tissues are damaged.

The adaptive immune system, on the other hand, continues to develop throughout our lives. When the body is attacked by a particular pathogen, the adaptive immune system "learns" how to combat that particular threat and then "remembers" this information, in the form of antibodies, for later use if the same germ is encountered again. Although boosting your immune system is not quite as simple as recharging a battery, there are certain foods capable of improving your immune function. Here's a look.

Chicken noodle soup

Is there anything more comforting when you're sick than chicken noodle soup? As it turns out, there's a good reason people reach for a big bowl of the stuff when they're feeling under the weather; it's packed with immune-boosting protein. According to Healthline, 3.5 ounces of chicken breast contains 31 grams of protein, while an equal-size portion of wing meat provides 30.5 g, drumsticks 28.3 g, and thighs 26 g.

Proteins like those in chicken noodle soup are made up of amino acids, and certain amino acids may be more important for the immune system than others. In a study published in Critical Care Medicine, the authors explained that the amino acid arginine "was demonstrated to enhance cellular immune mechanisms, in particular T-cell function." The researchers also noted that arginine helps preserve the immune system when it's weakened by low overall protein intake.

Glutamine is another amino acid critical for immune function. A 2018 paper published in Nutrients found that glutamine was essential for lymphocyte proliferation. This is the process by which lymphocytes "remember" specific pathogens so that they can defeat them again in the future. Macrophages also need glutamine to secrete their germ-killing substances and "eat" invading or damaged cells. Glutamine is also used by natural killer cells when they attack bacteria.

Orange juice

When you hear the words "immune booster," the first thing that probably comes to mind is vitamin C. Orange juice is the poster child for this important micronutrient, and for good reason: One cup has 124 mg of vitamin C, or almost 138 percent of the recommended daily allowance. That said, chugging glass after glass of the stuff when you're feeling under the weather is not a cure-all.

In an interview with Harvard Health, Dr. Bruce Bistrian, chief of clinical nutrition at Beth Israel Deaconess Medical Center, debunked the popular belief that vitamin C is a magic bullet against the common cold. He explained, "The data show that vitamin C is only marginally beneficial when it comes to the common cold."

Some research suggests that large doses of supplemental vitamin C may help extremely active people like marathon runners, but not the general population, avoid getting sick. Another study, however, found that getting more than 200 mg a day shortened colds by 8 percent among adults and 14 percent among children — equivalent to one fewer sick days.

Guava

When it comes to vitamin C, nothing packs more punch than guava. This exotic tropical fruit contains 377 mg — an incredible 419 percent of your recommended daily allowance — in just one cup. Although all that vitamin C may not be able to miraculously cure a cold, it's an absolutely necessary prerequisite for a well-functioning immune system.

Our skin is part of our innate immune system and the first line of defense against invading germs. According to a 2017 article published in Nutrients, vitamin C is vital for the production of collagen, the protein that gives skin its structure. It also accumulates in phagocytes, a group of white blood cells that require this vitamin to destroy germs by engulfing and essentially "eating" them.

Additionally, vitamin C is needed for apoptosis, the destruction and recycling of old or damaged cells that could otherwise cause harm in the body. Vitamin C helps lymphocytes, another type of white blood cell that's part of the adaptive immune system, differentiate into specialized B and T cells, designed to target specific invaders the body has encountered in the past. The article's authors pointed out that vitamin C deficiency "results in impaired immunity and higher susceptibility to infections."

Oysters

Zinc is a micronutrient essential for the immune system, and there's basically no better source than oysters. According to Healthline, six medium oysters contain 32 mg — a whopping 291 percent of the recommended daily intake.

A paper published in Molecular Medicine noted that, in addition to having powerful antioxidant and anti-inflammatory properties, zinc is essential for many types of immune cells. It's needed for the "normal development and function of cells mediating innate immunity, neutrophils, and NK [natural killer] cells." Zinc supplementation "reduced the incidence and duration of acute and chronic diarrhea and acute lower respiratory tract infections in infants and children." It also reduced the number of cases of pneumonia and E. coli urinary tract infections. Zinc deficiency, on the other hand, impedes the immune system, thus increasing your chances of infection, according to Healthline.

If you can't stomach oysters or are allergic to shellfish, other good sources of zinc include meat, hemp seeds, cashews, and cheese, although none of these have anywhere near as much zinc as oysters.

Brazil nuts

Selenium is a trace mineral you may have never heard of, but it has a complex relationship with immune function. Adults need 55 micrograms daily, while pregnant and breastfeeding women need 60 mcg. Although selenium is found in both plant and animal foods, Brazil nuts are by far the best source. Just one ounce (six to eight nuts) contains 544 mcg — almost 10 times the recommended daily amount. In fact, you should only eat Brazil nuts a few times a week to avoid getting too much selenium.

A paper published in Molecular Nutrition & Food Research noted that "the notion that [selenium] 'boosts' the immune system has been supported by studies involving aging immunity or protection against certain pathogens." In the case of viral infections and protection against cancer, higher levels of selenium appear to be beneficial.

This may not be the case when it comes to bacterial, fungal, or parasitic infections, however. It's also unclear how selenium affects the immune system in the case of allergies and asthma, with some studies suggesting it "may not always be beneficial." Nevertheless, Healthline advised, "Selenium is crucial for the health and proper functioning of your immune system."

Lentils

Iron deficiency is extremely common, affecting 3 percent of men, 20 percent of non-pregnant women, and 50 percent of pregnant women, according to WebMD. In addition to causing anemia, low iron levels can have a negative impact on the immune system.

A paper published in Basic Neurosciences, Genetics and Immunology explained that iron levels in the body are important because our own immune cells need iron for growth. The genes and proteins that control iron balance in the body can produce temporary fluctuations in a way that prevents invading bacteria from stealing it. That doens't mean you should overload on iron, though. "Both iron deficiency and iron excess can compromise cellular function," a 2011 study found.

If you need more iron in your diet, you're in luck. Iron comes in two forms: heme (from animal foods) and non-heme (from plant foods). Although heme iron is easier for your body to absorb, non-heme iron is also a great addition to your diet. Lentils are one of the richest sources of non-heme iron; a half-cup of cooked lentils gives you 15 percent of your recommended daily allowance of iron.

Beef liver

Not everyone loves its strong taste and unique texture, but liver can do your immune system a big favor. In addition to being a rich source of immune-boosting zinc, iron, and protein, liver is packed with vitamin A. A 3-ounce serving of fried beef liver contains 6,582 mcg — a staggering 731 percent of the recommended daily value. Because vitamin A is fat-soluble and can accumulate in body tissues, however, it's important to consume liver in moderation.

A 2018 paper published in the Journal of Clinical Medicine noted that vitamin A has a "critical role in enhancing immune function." It's particularly important for "protecting epithelium and mucus integrity," which means it helps to maintain the mucus membranes that serve as our first line of defense against invading germs.

Yet, according to Oregon State University, 43 percent of American adults don't get enough vitamin A. If the idea of eating liver is unappetizing, you can take liver supplements or opt for other foods high in vitamin A, like sweet potato, carrots, and spinach.

Salmon

One of the best ways for the body to get vitamin D is from the sun, but if you spend lots of time indoors, live in northern parts of the United States, have dark skin, or always slather on the sunscreen, you're likely not getting enough. In fact, an estimated 42 percent of Americans are vitamin D deficient.

Thankfully, you can get more vitamin D through your diet. Some foods are fortified with vitamin D, and fatty fish are the best dietary sources of this important nutrient. According to Healthline, a 3.5-ounce serving of farm-raised salmon contains between 250 and 526 IU of vitamin D, while the same size portion of wild salmon has between 988 and 1,300 IU.

Although vitamin D is best known for its role in calcium absorption and bone health, a paper published in the Journal of Investigative Medicine pointed out that it's also essential for proper immune functioning. The authors noted that people have unknowingly been using vitamin D for hundreds of years to help treat disease. For example, individuals with tuberculosis were often given cod liver oil and encouraged to sunbathe. Conversely, being vitamin D deficient puts individuals at greater risk for autoimmune conditions and infections.

Sunflower seeds

Sunflower seeds are one of the richest dietary sources of vitamin E available. A single ounce contains 10 mg of this important immune booster — 66 percent of the amount you should be getting each day. Vitamin E is a powerful antioxidant — but what exactly does that mean?

Antioxidants are chemicals that protect the body against damage from free radicals, which are highly unstable atoms of oxygen that try to "steal" electrons from other molecules in the body. This destabilizes those molecules and creates a chain reaction that leads to damage throughout the body. This process is known as oxidative damage or oxidative stress and contributes to aging and the development of diseases such as cancer, heart disease, and Alzheimer's. Substances that produce free radicals can be found in food and in our environment, and free radicals are also created as the byproduct of natural chemical processes in the body. Thankfully, antioxidants are able to give free radicals the electrons they want without becoming destabilized themselves.

Although severe vitamin E deficiency is rare in the United States, Oregon State University noted that 88.5 percent of individuals don't meet the recommended requirement of 12 mg. Sunflower seeds to the rescue!

Sauerkraut

You likely already know how important probiotic foods are for your beneficial gut bacteria and digestive health, but did you know that these "living" foods can also boost your immune system? That's because, according to Essentia Health, approximately 70 percent of your immune system resides in your gut. Eating probiotic foods can reduce your risk for respiratory infections such as the common cold. Essentia Health noted that "certain probiotic strains, Lactobacillus and Bifidobacterium, were found to lessen the duration of respiratory infections in adults and children."

Probiotic foods also offer protection against some foodborne pathogens. A study published in the journal Gut concluded that two probiotic strains, Streptococcus thermophilus and Lactobacillus acidophilus, protect the epithelial cells lining the intestinal tract from E. coli. These probiotic strains appear to make it more difficult for E. coli to adhere to and penetrate these epithelial cells.

Sauerkraut, or fermented cabbage, is an especially great probiotic. According to Healthline, it may contain up to 28 different strains of beneficial bacteria. Just one gram of sauerkraut boasts between 1,000 and 100 million colony-forming units (CFUs) of bacteria. To put that into perspective, probiotic supplements contain 1-50 billion CFUs.

Garlic

In addition to keeping vampires at bay, garlic may be able to ward off bacteria and other disease-causing microorganisms. A 2014 paper published in the Avicenna Journal of Phytomedicine attributed garlic's antimicrobial properties to a compound known as allicin. Garlic may be effective against a wide range of pathogens, including Salmonella, E. coli, Staphylococcus, and candida (yeast).

Interestingly, garlic appears to harm disease-causing microorganisms while leaving the beneficial ones in our gut unharmed. The researchers noted that "garlic has been found to contain a large number of potent bioactive compounds with anticancer properties." It may be able to inhibit the activation of carcinogens, protect DNA from activated carcinogens, and improve the body's ability to detoxify.

Preliminary research suggests that garlic may even be able to help prevent the common cold. In a study published in Advances in Therapy, researchers gave 146 participants either garlic pills or a placebo and observed for 12 weeks. Among those receiving the garlic, there were 24 colds, while the placebo group had 65. The garlic group experienced cold symptoms for only about a day and a half, while those in the placebo group took an average of a little over five days to feel better.

Reishi mushrooms

Although relatively new to American consumers, reishi mushrooms have been used for thousands of years as an immune-booster in Asia. According to the National Cancer Institute, these mushrooms were "considered a superior tonic for prolonging life, preventing aging, and boosting qi" in traditional Chinese medicine. Even today, Chinese physicians prescribe them as an immune booster to patients undergoing cancer treatment.

Although there are few human studies on reishi, preliminary research suggests that it may prevent cancer cells from secreting substances that suppress the immune system, the institute explained. The mushrooms may also prevent the growth of precancerous cells in the colon. The mushrooms' immune-boosting benefits are attributed to beta-glucans, long chains of complex carbohydrates.

The Memorial Sloan Kattering Cancer Center noted that reishi mushrooms may also reduce inflammation, lower cholesterol and blood pressure, combat fatigue, and improve stamina. Reishi mushrooms can be consumed in a few ways, including as a liquid extract or loose powder.

Echinacea

When it comes to herbal supplements for strengthening the immune system, echinacea is perhaps the most popular choice. A paper published in Advances in Integrative Medicine in 2020 noted that "current evidence suggests that echinacea supplementation may decrease the duration and severity of acute respiratory tract infections." The authors wanted to investigate whether the herb might also assist — or hinder — in the prevention or treatment of COVID-19 infections. 

Although there were no studies specifically examining echinacea's effects on the novel coronavirus strain, the researchers analyzed studies that examined either the herb's effects on similar viruses or its effects on cytokine production. Cytokines are signaling molecules that help coordinate our immune response. Too much cytokine activity, known as a "cytokine storm," can be dangerous, even deadly, and such immune overreactions may be at the heart of the most severe coronavirus cases. Fortunately, the researchers found that echinacea "decreases levels of immune molecules involved in cytokine storm[s]." Echinacea can be purchased in a variety of forms, including as dried herbs, tea, capsules, and liquid extract.

Ginseng

Ever notice that you're more likely to come down with a cold when you're stressed out? It's not a coincidence. The American Psychological Association explained that chronic stress wears down and weakens the immune system. They noted that "for stress of any significant duration — from a few days to a few months or years, as happens in real life — all aspects of immunity [go] downhill."

Ginseng is an herb (and, by the way, an aphrodisiac) that has been used as a traditional medicine for hundreds of years. It can boost immunity by controlling our body's stress response. A 2017 paper published in the Journal of Ginseng Research found that "ginseng regulates the hypothalamic–pituitary–adrenal (HPA) axis. ... The HPA axis is the major pathway regulating the immune response to stress." Another paper, published in the same journal in 2012, noted that ginseng can influence the activity of many types of immune cells, and it can also be beneficial in combatting infections and inflammatory diseases.

Fortunately, ginseng is widely available. There are two main varieties — Korean and American — and both can be purchased as dried herbs, tea, loose powder, and capsules.