When it’s flu season or if ill, people often seek something that will prevent getting sick or help them recover faster, turning to special foods or vitamin supplements that are believed to boost immunity. However, the immune system is complex and affected by many factors. What role does diet play in your immune system? Can a specific diet keep you healthy? Does eating certain foods when you’re sick help you feel better sooner?
The immune system is constantly protecting the body from antigens, which are substances that the body labels as foreign and harmful, such as bacteria, toxins, parasites, and viruses. All trigger immune cell activity. Humans have two types of immunity: innate and adaptive.
Innate immunity is the first-line defense from pathogens that try to enter our bodies. It consists of physical barriers, such as:
- Skin (keeps out most pathogens)
- Mucus (traps pathogens)
- Stomach acid (destroys pathogens)
- Enzymes in our sweat and tears (help create anti-bacterial compounds)
- Immune system cells (attack all foreign cells entering the body)
The innate immune system is nonspecific because it reacts similarly to all foreign invaders. When pathogens attack healthy cells, immune cells (mast cells) counterattack and release proteins (histamines), resulting in inflammation. While it may generate pain and swelling, it also causes a release of fluids to help flush out the pathogens. In addition, the histamines send signals to release more white blood cells to fight pathogens. So, in this sense, inflammation is good.
However, prolonged inflammation can cause tissue damage and may overwhelm the immune system. Studies have shown that chronic inflammation has been linked to cancer, heart disease, diabetes, arthritis, depression, Alzheimer’s, and many other conditions.
If the innate immune system is unsuccessful at defeating a potential threat, the adaptive immune system takes over. It involves specialized blood cells and proteins that target the specific cause of infection. Adaptive immunity is a system that learns to recognize a pathogen, meaning it has a “memory.” This explains why a person’s body can become immune to specific illnesses.
The adaptive immune system is regulated by cells and organs in our body, such as the spleen, thymus, bone marrow, and lymph nodes. So, when a foreign substance enters the body, they create antibodies and lead to the development of immune cells specific to that harmful substance to attack and destroy it.
What Items can Suppress the Immune System?
Many things can adversely affect the body’s immune function, like certain illnesses, medications, and lifestyle choices.
Stress is one thing most people know negatively impacts the immune system. When the body is stressed, it releases hormones, such as cortisol, that suppress inflammation. Since inflammation is initially needed to activate immune cells and the action of white blood cells, this can be problematic.
Sleep is when the body restores itself. During sleep, cytokines are released; these fight infections. Thus, too little sleep lowers the amount of these protective cytokines and other immune cells.
Environmental toxins, like air pollution or excessive alcohol consumption, can impair or suppress the normal activity of immune cells.
Aging is associated with a couple of things that impact the immune system. The first is that our internal organs often become less efficient as we age, and immune-related organs produce fewer immune cells. The second item is aging is sometimes connected to micronutrient deficiencies, which may worsen a declining immune function.
Obesity is another problem with increased infections because it’s associated with low-grade chronic inflammation. Also, fat tissue produces adipocytokines that increase the inflammatory processes.
Autoimmune and immunodeficiency disorders are similar in that they hinder the immune system. Autoimmune diseases are partly hereditary and trigger hypersensitivity in which immune cells attack and destroy healthy cells. Immunodeficiency disorders can be genetic or acquired (more common) and weaken or completely disable the immune system, resulting in the person becoming highly susceptible to illness from invading pathogens or antigens.
How Does Diet Impact the Immune System?
Like all other aspects of health, studies indicate that a person’s diet influences their immune system. Eating enough nutrients as part of a diverse diet is essential for the health and function of all cells. Each stage of the body’s immune response relies on the presence of many micronutrients. A deficiency of single nutrients can alter the body’s immune response.
Some nutrients that have been found to be critical for immune cells include vitamin C, vitamin D, vitamin A, vitamin B6, vitamin E, zinc, selenium, iron, copper, folic acid, and protein (including the amino acid glutamine). They are located in a variety of plant and animal foods. These nutrients help in several ways: working as an antioxidant to protect healthy cells, supporting the growth and activity of immune cells, and producing antibodies. Epidemiological studies demonstrate that poorly nourished people are at greater risk of infections. Malnutrition occurs when a person’s diet lacks one or more nutrients.
The microbiome is comprised of trillions of microorganisms or microbes that live in our bodies, mainly in the intestines. Scientists are finding that it plays a crucial role in immune function because the gut is a major site of immune activity and produces antimicrobial proteins. It’s estimated that 70% of the immune system is housed. Therefore, a healthy microbiome is crucial to immune function.
Diets that consist primarily of ultra-processed foods and lack minimally processed foods are limited in variety and lower in nutrients, which can negatively affect the immune system. Western diets tend to contain ultra-processed foods high in refined carbohydrates, saturated fat, added sugar, salt, and overall calories. This diet is also often low in vegetables, fruits, and fatty fish. So, it’s no wonder Western diets promote disturbances in healthy intestinal microorganisms from nutrient deficiencies.
Foods and beverages that impact blood sugar levels, like soda, candy, sugary cereals, and sugary baked goods, raise levels of inflammatory proteins. Also, they interfere with the function of protective immune cells, including neutrophils and phagocytes. Diets high in added sugar and refined carbs can negatively alter gut bacteria, leading to dysbiosis, which involves digestive disturbances, such as bloating.
Studies reveal that diets high in saturated fat might cause inflammation, alter gut bacteria, and hinder the functioning of white blood cells. High salt diets have been linked to excessive immune response, decreased inflammation regulation in the body, and an elevated risk of certain autoimmune diseases, like rheumatoid arthritis. When the body has too much inflammation, the immune system struggles.
Research is starting to show that eating a lot of ultra-processed foods may shorten your life. Just a 10% increase in consuming these foods was associated with a 14% higher risk of death from all causes.
A diet rich in vegetables, fruits, nuts, legumes, and seafood and low in ultra-processed foods can decrease disease risk and encourage healthy immune function. Foods with high amounts of healthy fats, fiber, vitamins, protein, minerals, and beneficial plant compounds decrease systemic inflammation, promote healthy gut bacteria balance, reduce oxidative stress and cellular damage, and improve blood sugar and insulin sensitivity. All of these activities are essential for healthy immune function.
One pattern of eating that follows this method is the Mediterranean. Numerous studies have shown that the Mediterranean diet can lower the risk for high cholesterol, dementia, memory loss, depression, and breast cancer. Also, it’s been linked to stronger bones, a healthier heart, weight loss, and longer life. Research has shown that it lowers markers of inflammation and helps modulate gut bacteria.
A Mediterranean diet involves eating lots of fruits, vegetables, lean proteins (ex. fish and poultry), legumes, nuts, seeds, olive oil (in moderation), and whole grains. It also means limiting or skipping certain foods, like processed meats (ex. hot dogs and bacon), red meat, sugar, desserts, processed/fried/fast foods, and white/refined grains.
The Mediterranean diet is also high in fiber, which stimulates the production of short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate. The SCFAs feed the beneficial microbes and help them maintain healthy colonies. These fibers are sometimes called prebiotics. Foods with prebiotics include garlic, onions, leeks, asparagus, Jerusalem artichokes, dandelion greens, bananas, and seaweed.
Prebiotics are different than probiotics. However, probiotics help the immune system too. Probiotic foods contain live helpful bacteria by initiating the responses by macrophages (a type of cell that engulfs harmful substances and rids them from the body). Eating plenty of fermented foods is an easy way to get them into your daily diet. Probiotic foods include yogurt with live active cultures (Greek yogurt), fermented vegetables, sauerkraut, miso, kombucha tea, kefir, kimchi, and tempeh.
SCFAs are end products of bacterial fermentation in the gut and act locally and systemically to modulate the immune response. SCFAs also maintain and improve the immune defensive function of the intestinal epithelium, which is an integral part of the immune system that serves as a barrier against microorganisms. In addition, SCFAs lessen the production of inflammatory proteins from immune cells.
Key Nutrients for the Immune System
Let’s take a closer look at the essential nutrients that have been identified as critical for the growth and function of immune cells.
Iron is a component of enzymes that is critical for immune cell function because it helps increase immune cell production and development associated with creating a specific response to infection. Some great options to get enough iron in your diet include red meat, beans, nuts, and fortified breakfast cereals.
Protein is essential for the immune system because it powers the body’s T-cells, immune cells that attack pathogens that get into your bloodstream and cause infection. It comes from animal and plant-based sources, such as milk, yogurt, eggs, beef, chicken, seafood, nuts, seeds, beans, and lentils.
Vitamin B6 plays a vital role in many chemical reactions that happen in the body, including those of the immune system. It’s also crucial for forming new and healthy red blood cells. You can add vitamin B6 to your diet by consuming beef liver, tuna, salmon, fortified cereals, chickpeas, poultry, and some vegetables and fruits, especially dark leafy greens, bananas, papayas, oranges, and cantaloupe.
Vitamin A protects against infections by keeping skin and tissues in the mouth, stomach, intestines, and respiratory system healthy. Beta-carotene is a precursor to vitamin A and turns into it when the body needs it. To get enough vitamin A, eat sweet potatoes, spinach, carrots, mango, broccoli, tomatoes, apricots, bell peppers, and orange and red fruits.
Vitamin C stimulates the formation of antibodies and the production, function, and movement of white blood cells. According to a review in Nutrients, it contributes to the rapid increase in two white blood cells (B cells and T cells) that play a role in secreting antibodies and killing off infections. Foods rich in vitamin C-rich include grapefruit, oranges, clementines, tangerines, lemons, limes, berries, melons, papayas, kiwis, tomatoes, bell peppers, and broccoli.
Many people think citrus fruits have the most vitamin C of any fruit or vegetable. However, ounce for ounce, red bell peppers contain almost three times as much vitamin C (127 mg) as a Florida orange (45 mg). They’re also a rich source of beta-carotene. Another great source of vitamin C is broccoli. In addition, it has vitamin A, vitamin E, fiber, and antioxidants, making it one of the healthiest vegetables you can eat. The key to reaping these benefits is to cook it as little as possible.
Spinach is also rich in vitamin C, antioxidants, and vitamin A and should be cooked minimally. Papaya is loaded with vitamin C—one medium fruit has double the daily recommended amount. It also has a digestive enzyme (papain) that has anti-inflammatory effects.
Even though many people believe taking high doses of vitamin C can prevent illness, research suggests otherwise. However, if you’re sick, taking in at least 200 milligrams (mg) of vitamin C per day may lessen the duration of cold symptoms a day for most people.
Vitamin D helps regulate antimicrobial proteins that can directly kill pathogens. The best way to get vitamin D is to spend some time outside because the body produces it after being exposed to sunlight. Food sources include fatty fish (ex. salmon), eggs, and fortified products (ex. dairy and juices). It’s essential to note that vitamin D toxicity can occur but is almost always from the overuse of supplements. Signs of toxicity are nausea, vomiting, poor appetite, constipation, weakness, and weight loss.
Vitamin E functions as an antioxidant to protect cell membranes from damage caused by free radicals. It’s also been shown to increase the percentage of T cells. You can get vitamin E through nuts, peanut butter, sunflower seeds, spinach, broccoli, tomatoes, avocados, and vegetable oils. Nuts, like almonds, are packed with vitamin E and have healthy fats. Sunflower seeds have vitamin E and other essential nutrients, including phosphorous, magnesium, selenium, and vitamin B6.
Zinc is needed for wound healing and supports immune response by helping the development of neutrophils (a type of white blood cell). Since zinc isn’t as prevalent in many foods, deficiencies can occur. It’s usually better absorbed from animal sources, but also is in vegetarian sources. Some good ways to include zinc in your diet are beef, oysters, crab, lobster, mussels, cashews, chickpeas, Greek yogurt, pumpkin seeds, lentils, milk, wheat germ, seeds, nuts, and tofu.
Although zinc won’t prevent you from catching a cold, like vitamin C, taking it at the onset of a cold might decrease its duration by a day. Keep in mind that too much zinc can inhibit immune system function, so don’t take too much frequently. Also, zinc can interfere with the effectiveness of antibiotics or negatively interact with some blood pressure and rheumatoid arthritis medications, so check with your doctor before taking it.
Herbal Supplements & the Immune System
Some people believe that herbal supplements boost immune function. What does the research say?
Echinacea: According to the data, taking echinacea after you’re already sick hasn’t been shown to shorten its duration. However, taking it when you’re healthy may offer a slight chance of protection from getting sick.
Garlic: Allicin sativum (the active ingredient in garlic) is thought to have antiviral and antimicrobial effects. Unfortunately, high-quality clinical trials comparing garlic supplements to placebo are lacking.
Ginger: Ginger may help decrease inflammation, which can help reduce a sore throat and inflammatory illnesses. Ginger may help with nausea as well. It may also decrease chronic pain and might even possess cholesterol-lowering properties.
Tea catechins: Studies of cells show that tea catechins can prevent the flu and some cold viruses from replicating and can increase immune activity. However, human trials are still limited. Both green and black teas are packed with flavonoids (an antioxidant). However, green tea has high levels of epigallocatechin gallate (EGCG), another powerful antioxidant. In studies, EGCG has been shown to enhance immune function. Black tea goes through a fermentation process that destroys many of the EGCG. Also, green tea has the amino acid L-theanine, which may aid in producing germ-fighting compounds in your T cells.
Turmeric: Turmeric has been used as an anti-inflammatory for osteoarthritis and rheumatoid arthritis for years. Research shows that it has high concentrations of curcumin, which gives turmeric its distinctive bright yellow color. From animal studies, curcumin has promise as an immune booster and an antiviral. However, more research is needed.
What About Chicken Soup?
When most of us are sick, we turn to chicken soup because there haven’t been claims that it aids in healing. Is there scientific evidence to back that up?
The short answer is no. There aren’t any studies demonstrating that chicken soup speeds healing any more than other foods. However, when breaking down its ingredients, it does appear it might have some benefits. First, chicken soup isn’t a heavy food, which is easy on the stomach when our appetite isn’t great.
Second, it provides fluids and electrolytes that help prevent dehydration, which can quickly occur with a fever. Third, chicken soup supplies various nutrients involved in the immune system: protein and zinc from the chicken, vitamin A from carrots, vitamin C from celery and onions, and antioxidants in the onions and herbs.
So, while it might not have scientific proof that it aids in healing, it definitely isn’t bad for you when you’re sick.
Food vs. Supplements
The question is often raised which is the better way to get all the nutrients the body needs—food or supplements?
Generally, a balanced diet is the best way to get adequate nutrition to maintain a strong immune system. However, certain populations can’t eat a variety of nutritious foods or have increased nutrient needs. For these individuals, vitamin and mineral supplements can help fill nutritional gaps. Some groups that are at risk include low-income households, pregnant and lactating women, infants and toddlers, and the critically ill.
Another high-risk group is the elderly. Statistics show that about one-third of the elderly in industrialized countries have nutrient deficiencies. As we age, the immune response generally declines as the number and quality of immune cells decrease. An older person with chronic or acute diseases is at even higher risk. Also, many are on multiple medications that can interfere with nutrient absorption and appetite. In addition, diet variety might be limited due to having less interest in cooking, budget constraints, or lack of transportation and community resources to obtain healthy food.
A multivitamin providing no more than 100% of the recommended daily allowance is generally safe for many people. However, individuals on any medications or with medical conditions should talk with a healthcare provider before starting any supplement. Definitely avoid “mega doses” that supply greater than 100% of the recommended daily amount since it doesn’t offer any additional benefit and can be harmful in some cases.
How to Get the Required Nutrients from Your Diet?
Variety is the key to proper nutrition because that provides the micronutrients the body needs to have a robust cellular immune response. It’s vital to pay attention to serving sizes and recommended daily intake so that you don’t get too much of a single vitamin and too little of others. Your goal should be to get at least five to seven servings of a large variety of fresh and colorful vegetables and fruits daily. This will provide the vitamins, minerals, and antioxidants to support immune health.
One 2017 study found a significant reduction in the risk of heart attack, stroke, cancer, and early death by eating ten portions of fruit and vegetables daily. This is more than the current dietary guidelines of at least 2 cups of fruit and 2.5 cups of vegetables a day and far higher than the 0.9 cups of fruit and 1.4 cups of vegetables per day the average American eats, according to surveys from the US Department of Agriculture. Besides fruits and vegetables, include some high-quality whole grains, a bit of lean protein, and a splash of healthy oils in your daily meal plan.
To help your immune system by lowering inflammation, change the type of fats you eat. Since saturated fats are a primary cause of inflammation, you’ll want to reduce your intake. This means decreasing the number of baked goods (ex. cookies and cakes), full-fat dairy (ex. cream, cheese, and butter), lard, palm oil, and red meat you consume.
Trans fats also cause inflammation and are bad for your heart. Avoid this entirely by staying away from foods containing “partially hydrogenated” oils. Even if the label says “zero grams of trans fat per serving,” it might still contain some because food manufacturers can make this claim if the product has less than 0.5 grams of trans fat per serving. Be wary of packaged foods and baked goods, such as biscuits, cookies, crackers, doughnuts, margarine, and pie crusts.
Since fatty fish are a good source of this anti-inflammatory fat, try eating more of them. Examples are albacore tuna, herring, mackerel, salmon, sardines, and trout. Some plant foods contain omega-3 fatty acids, which are good for you. They can be found in canola oil, chia seeds, edamame, milled flaxseeds, flaxseed oil, pumpkin seeds, and walnuts.
It can be challenging to change your diet, so start gradually. You can try switching from white, refined bread to whole-grain bread or having fruit for dessert instead of baked goods. Once you’re comfortable with those changes, change something else. One option is replacing red and processed meat with fish and lean chicken. Another choice is swapping fat-free milk for full fat.
Other Important Steps to Having a Better Immune System
In addition to eating well, there are other vital things to do that can help keep you healthy. It’s essential to maintain a healthy weight by getting moderate exercise several times a week. Another critical step is getting 7 – 9 hours of sleep every night. It’s a good idea to have a sleep schedule that involves waking up and going to bed around the same time each day. Reducing stress is very important, which you can do through exercise, meditation, a particular hobby, or talking to a trusted friend. Don’t smoke, or stop smoking if you do. Only drink alcohol in moderation.
Good hygiene and handwashing helps prevent the spread of germs, so be sure to remember to wash your hands throughout the day. Always wash produce before eating or using it in recipes. Be sure to clean glasses, forks, spoons, and other utensils to reduce the spread and growth of bacteria.
While a good diet can’t boost the immune system, it’s key to maintaining a functional immune system by avoiding malnutrition or micronutrient deficiencies. To support immune function, focus on a balanced diet with lots of whole, nutrient-dense foods while avoiding ultra-processed foods. Remember that supplements shouldn’t be considered a substitute for a good diet. In addition, the immune system is incredibly complex and influenced by a variety of other factors, so be sure to manage these as well.
Combining a balanced diet with healthy lifestyle factors ensures the body is ready to fight infection and disease.