Disclaimer: The information on this page is general in nature. It is not specific to the coronavirus (COVID-19). Please consult with your healthcare provider before making any changes to your diet.
As a Dietitian and a healthcare professional, I’ve been asked lately about how does nutrition affect the immune system. People want to know if there are certain foods and supplements that they can take to “boost” immunity and avoid getting sick. “Are there foods that can boost my immunity?”, “Can ‘X’ supplement improve my immune system?” and “What can I eat to help fight or prevent infection?” are some of the questions I’ve been getting lately.
In this post, I’ll cover the relationship between nutrition and the immune system, and whether you actually can naturally improve your immune system, or if it’s just a lot of misleading information. Keep reading to see what the latest evidence has to say on how does nutrition affect the immune system .
An ultra-simplified overview of the immune system
A healthy immune system is vital to providing good defense against germs and to providing tolerance to non-threatening organisms, to food components and to self. The immune system works by:
- Providing a selective barrier
- Identifying and eliminating pathogens (the germs that make us sick)
- Identifying and tolerating non-threatening sources of antigens (such as food)
- Maintaining a memory of immunological encounters (this is how vaccines work)
OK, first of all, we have to understand that the immune system is made up of cells, tissues, and organs that work together to protect your body from illness and infection. Therefore, the immune system is not just one single “thing”, and so it follows that there isn’t a single food or certain foods that you can eat or add to your diet to “boost” immunity.
This particular article summarizes it the following way: “The notion that the immune system is something that we can easily influence is cast into doubt when you realize how complicated it really is. There are hundreds of different types of cells in the immune system doing a variety of jobs whether it’s identifying invaders, carrying messages, devouring known bacteria or learning how to fight new enemies”.
However, you can eat to support your immune function by making sure you have all the energy, vitamins, minerals and macronutrients you need, as we’re about to see later on. We’ll also see the distinction between “supporting” and “boosting” when it comes to protection against infections.
Relationship between nutrition and immunity
OK, so we can agree that adequate and balanced nutrition is necessary for our cells to function optimally, including immune cells, right? We need sufficient energy in the form of calories and the right amount of nutrients so our cells can do their thing.
Adequate nutrition is essential for proper immune function. For example, this paper from Nutrients states that when the immune system is “activated” (when you get sick, for example), it “increases the demand for energy during periods of infection…Thus, optimal nutrition for the best immunological outcomes would be nutrition, which supports the functions of immune cells allowing them to initiate effective responses against pathogens but also to resolve the response rapidly when necessary and to avoid any underlying chronic inflammation. The immune system’s demands for energy and nutrients can be met from exogenous sources i.e., the diet, or if dietary sources are inadequate, from endogenous sources such as body stores”.
In other words, we have to eat enough energy (calories) and nutrients in order to help the immune system do its job efficiently, and even more so when there is an illness present.
We can also see the relationship between the immune system and the lack of good nutrition. Malnutrition can, in fact, weaken immune function. The relationship between malnutrition and immune dysfunction “may be a bit ‘chicken and egg’, with both causing and being the consequence of the other, as this article very well puts it. In fact, this review from Trends in Immunology states that immune dysfunction can directly drive disease processes when there’s malnutrition, including:
- Nutrient malabsorption
- Increased metabolic (caloric) demands
- Dysregulation of growth hormone axes (when there is an imbalance between hormones that work together to make you grow)
- Greater susceptibility to infection
In other words, when we’re not adequately nourished, the immune system can become out of whack, requiring more calories and affecting the absorption of nutrients, which in turn worsens malnutrition, and…you get the point. Chicken and egg indeed.
Although it’s not fully clear how exactly malnutrition and immune function are related, it seems that the following factors are involved:
- Reduced numbers of white blood cells, the ones involved in fighting infections and foreign invaders
- Weaker skin and gut membranes, which makes it easier for germs to enter the body
- Faulty lymph nodes, which function as filters that trap germs
It’s also important to note that the severity of, shall we say, a “weakened” immune system will depend upon the severity of the nutritional deficiency, whether there are nutrient interactions to consider, if an infection is present, and the age of the person. So, as with all things health related, there is not really a “one size fits all” approach.
And although there’s still much more research to be done, the evidence for the impact of the immune dysfunction in malnutrition continues to grow.
Immune system booster foods: do they really work?
So now on to what you probably really came here for. Are there any foods you can regularly eat to boost your immune system and avoid getting sick? Well, the answer is: it’s complicated.
As we saw above, the immune system is very complex, so it’s not really as simple as gargling lemon water or taking Echinacea and suddenly I’m able to fight germs more powerfully.
For example, I spoke to Dr. Heidi Morales, Immunologist at Abbvie Pharmaceuticals, who states that: “There is little evidence to support the notion that specific diets and supplements effectively boost your immune system. Fruits and vegetables provide the necessary vitamins and minerals that help maintain cellular health. Managing your stress with activities like moderate exercise can help keep your cortisone levels down, leveling immune system function. Proper hydration improves circulation and helps your body get rid of toxins that may inadvertently trigger an immune reaction and inflammation”. We just don’t have enough evidence to conclude that “x” food, diet or supplement directly improves immune function.
However, there are some nutrients that, when we don’t get enough of them, can negatively affect immunity. Let’s check out which nutrients, and food sources, are most associated with immune function and what effect they really have on it.
Nutrients most associated with immune function
There are many nutrients involved with immune function, but the micronutrients with the strongest evidence for immune support are vitamins C and D and zinc. There is also increasing interest in the role of non-nutritive substances such as probiotics and tea components, which I will also discuss.
Zinc is known to be an important micronutrient for the immune system. Even a mild zinc deficiency has been associated with defects in immune response. When the body is not getting enough zinc, per this review,the following may occur:
- Impaired formation, activation, and maturation of lymphocytes, one of the main types of immune cells
- Faulty communication between cells via cytokines, proteins involved in cell signals
- Weakened host defenses
Zinc is also required to ensure the structural and functional integrity of the skin and all mucus membranes, which form physical and chemical barriers that represent a first line of defense against germs.
However, as this article states: “the assumption that zinc supplementation would enhance immune response has been frustrating and full of controversy”. For example, it is thought that zinc supplementation, especially in the form of lozenges, helps reduce the duration of the common cold.
However, most of the evidence, such as this recent trial, have not proven this to be consistently effective. A zinc deficiency would best be addressed and treated by a health professional, instead of over the counter supplements.
A daily intake of zinc is required to maintain a steady state because the body doesn’t really have a way to store it. Recommended Dietary Allowance (RDA) quantities of zinc have been established for males age 14 and older as 11 mg/day, and females 19 and older at 8 mg/day. Here are the foods that provide zinc in your diet.
Food sources: Oysters, crab, lobster, red meat, poultry, beans, nuts, whole grains, fortified breakfast cereals, and dairy products
Vitamin C is the micronutrient most popularly associated with immune function. All you have to do is sneeze to get some well meaning advice to “make sure you stock up on vitamin C”. In fact, historically, the importance of micronutrients and the immune system was based on vitamin C deficiency and scurvy.
Some of the ways vitamin C contributes to immune defense is by supporting:
- Barrier functions at skin level, which also helps protect against environmental oxidative stress and promotes wound healing
- Microbial killing
- Decreasing potential tissue damage during infection
- Gene regulation
It is also a very powerful antioxidant, protecting important molecules in the body from damage by oxidants which show up during normal metabolic processes and through exposure to toxins and pollutants.
Vitamin C appears to be able to both prevent and treat respiratory and systemic infections by enhancing various immune cell functions. As this paper from Nutrients states, “prevention of infection requires dietary vitamin C intakes that provide at least adequate, if not saturating plasma levels (i.e., 100–200 mg/day), which optimize cell and tissue levels. In contrast, treatment of established infections requires significantly higher (gram) doses of the vitamin to compensate for the increased metabolic demand”. However, when using vitamin C for prevention, it’s important to have a healthcare professional determine how much your specific needs are.
The Recommended Dietary Allowance (RDA) for adults for vitamin C is set at 75 mg/day for females and 90 mg/day for males.
When you don’t get enough vitamin C, the immune system becomes impaired and there’s an increased chance of infection. Vitamin C is a water soluble vitamin (meaning it dissolves in water vs fat), so the body can’t really store it very well. It is therefore very important to ensure you get your necessary amounts on a daily basis.
Food sources: Fruits and vegetables such as citrus fruits and their juice (oranges, lemons, grapefruit), tomatoes and tomato juice, potatoes, red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, cantaloupe, and fortified cereals.
Epidemiological studies support the association between a healthy immune system and vitamin D. Deficiency of vitamin D has been associated with increased risk for Mycobacterium tuberculosis infection and other respiratory infections. This risk has been associated with compromised immune defense mechanisms. Cells of the immune system actually have vitamin D receptors, which highlights the importance of this nutrient.
In terms of infections, vitamin D seems to enhance:
- Attraction of immune cells towards the invader in order to destroy it
- The “eating” of microbes by immune cells, or phagocytosis
- Production of proteins that kill germs
Although the results of research on the potential benefits of administering vitamin D to decrease infection have not been consistent, this seems to be most likely due to methodology issues. However, there’s promise, such as this study which demonstrated that “a therapeutic dose of vitamin D showed that vitamin D administration resulted in a statistically significant (42%) decrease in the incidence of influenza infection”.
Vitamin D is a fat-soluble vitamin that is naturally present in only very few foods. It’s also added to others, and available as a dietary supplement. This vitamin is also produced in the body when ultraviolet rays from sunlight reach the skin and trigger vitamin D synthesis. Since vitamin D deficiency is quite prevalent, it’s important to check with your doctor to see if you need supplementation.
The RDA for vitamin D is set at 600 IU (15 mcg) for males and females 14-70 years old.
Food sources: Fatty fish (such as salmon, tuna, and mackerel) and fish liver oils, beef liver, egg yolks, some mushrooms; fortified foods such as milk, ready-to-eat breakfast cereals, some brands of orange juice, yogurt, margarine, plant milk alternatives (soy, almond, or oat).
The majority of immune cells within the human body are found within the gut-associated lymphoid tissue (GALT), or the digestive system, which is why this immune tissue is especially important in maintaining your health.
Probiotics are getting a lot of attention lately, in large part due to their role in digestive and immune health and although still more research is needed, we do know that some of the ways probiotics support the immune system is by:
- Maintaining the balance and suppressing the growth of potential pathogenic bacteria in the gut
- Reinforcing the intestinal barrier
- Decreasing gut inflammatory responses
Probiotics also protect against germ invasion by:
- Direct killing
- Competing with nutrients
- Enhancing the gut-associated immune response
You can get probiotics in your digestive system by eating more fermented foods and by probiotic supplements. Fermented foods are the best source, since probiotic supplements are usually recommended to treat specific health conditions (by your doctor), and not really recommended for everyday use. Also, supplements aren’t regulated by the FDA.
During fermentation, natural bacteria feed on the sugar and starch in the food, creating lactic acid. This process in turns creates an environment that promotes beneficial enzymes, B complex vitamins, omega-3 fatty acids, and various species of “good” bacteria.
Currently, there are no specific recommendations as to how much probiotics to take daily, but the general guideline is to add as many fermented foods to your diet as possible. If you think you might benefit from a probiotic supplement, please consult with a healthcare professional first.
Food sources: Fermented foods such as yogurt, kefir, kombucha, sauerkraut, pickles, miso, tempeh, kimchi, sourdough bread and some cheeses
Tea is the most widely consumed beverage in the world, next to water. There is often a misconception, that herbal tea is also tea. However, herbal tea is not made from the plant Camellia sinensis, the green tea plant.
Some studies have reported that tea catechins (which are disease-fighting flavonoids and antioxidants in tea) inhibited replication of the influenza virus and were also effective against some cold viruses. In addition, tea catechins may also enhance immunity against viral infections. However, as this paper in Molecules states, “Although the antiviral activity of tea catechins has been demonstrated, the clinical evidence to support their utility remains inconclusive”. So we have to tread with some prudence.
Some of the ways tea catechins and polyphenols are thought to help impede influenza viral replication is by:
- Inhibiting the interaction of a virus with the cell membrane when it invades a cell
- Increasing in natural killer (NK) cell activity
- Suppressing viral genome replication and viral protein expression
Although the amount of tea intake required for health benefits varies greatly among studies, drinking a minimum of three to five (8 oz) cups of green tea per day seems to be the general recommendation. Green tea overall has the highest amounts of catechins, while oolong and black tea have significantly less amounts. It also has less caffeine than black tea.
Brewing seems to have an effect on green tea antioxidant content. For example, this study observed that the amount of certain catechins “increased rapidly for the first 3–5 min of brewing at 85 °C, and increased brewing time resulted in a decrease in the yield of epistructured catechins”. Most of the research I reviewed has found that milled leaves steeped between 2-5 minutes optimally boost the polyphenol content in green tea that’s been brewed with hot water.
Food sources: Commercial green tea bags, loose green tea leaves, milled green tea leaves
How about supplements to boost the immune system?
Chances are, when you step into any pharmacy or even supermarket there will be a myriad of over the counter (OTC) supplements, teas and extracts that tout that they can help “boost your immune system”, “ward off viruses” and “keep you healthy”.
Here’s a select list of some of the most common ingredients in OTC dietary supplements aimed at “boosting” the immune system:
- Vitamin C
- Ginger root
- Mushroom extracts
- Astragalus root
- Green tea extract
- Apple cider vinegar
Just to name a few! There are also blends with a wide variety of “natural” ingredients that also promise to ramp up your immune system.
However, although there is some truth to the idea that vitamin supplements can help immunity, this is only in people who have a severe deficiency.
For example, someone with iron deficiency anemia may be more susceptible to infections, and would benefit from an iron supplement. However, a healthy person who starts taking iron for the purpose of “boosting immunity” won’t really get any significant benefit. And it’s also worth noting that for some micronutrients, such as iron, excessive intake can also be associated with impaired immune responses, as well as mineral, vitamin, herb and supplement toxicity.
And although some of these vitamin and herbal supplements may have some research behind them, the evidence is still not conclusive. Yes, there is plenty of anecdotal evidence, and I’m not saying they never work on anyone, but the jury is still out on whether these supplements can provide real, consistent and reliable results in large populations.
It’s also important to note that the claims on these products are not approved by the Food and Drug Administration (FDA). These supplements are not only potentially ineffective, but they could also interfere with other medications or treatments. For more on the safety (or lack thereof) of dietary supplements, here’s a handy resource from the FDA.
Warning: Do Not start taking any new supplement or medications without talking to your health care provider first.
Another factor to consider when thinking in terms of “boosting” is that “a hyperactive immune system can cause such problems as allergies, diabetes, and other types of autoinflammatory and autoimmune disorders…it could trigger autoimmunity and other problems”, according to this Harvard Health Publishing article. That’s why it’s better to think in terms of supporting our immune system, by getting the necessary energy and nutrients it needs to do its job.
It’s best to get these nutrients from foods instead of supplements. Unless your healthcare provider recommends you take a vitamin or supplement, you likely do not need one. The best way to include these nutrients is by eating whole foods.
So be very wary of these dietary supplements. At the most they may cause allergic reactions, food-supplement interaction, supplement-drug interaction or other adverse effects. At the least, they’ll do…nothing. As the above mentioned Harvard publication very well puts it: “Your money might be better spent on something else”.
Can a bad diet affect your immune system?
As we’ve just seen, there are some nutrients that help support a healthy immune system. It needs to get enough energy and nutrients in order to do its job of defending us against infections and disease.
Therefore, if we’re not fueling up our body properly, immune function can be compromised, as we’ve also just seen. A diet that does not include sufficient calories, protein, vitamins, minerals and antioxidants can definitely affect the immune system in a negative way.
Need an idea of how many calories you need and how much of each food group to include daily? Check out the MyPlate Plan right here:
How to support your immune system through nutrition and healthy habits
So what can we do in order for our diet to help us maintain healthy immunity? Here are some tips:
- Make sure to include a wide variety of nutrient rich foods in your diet. Fruits, vegetables, whole grains, lean meats, fatty fish, beans and legumes, nuts, seeds and plant based oils are some great examples
- Try to include from 5-9 servings of fruits and vegetables daily. Don’t like their taste? Try them in a delicious smoothie!
- Avoid processed foods as much as possible. This includes pre-packaged, convenience items such as microwave meals, ready to eat meals, snack chips, sweet snacks, juice drinks, canned meat products, processed cheese products, etc.
- Try to cut back on added sugars as much as possible
- Incorporate more fermented foods daily. Yogurt is a great place to start
- Gradually switch from sweetened beverages to plain water, infused water or unsweetened tea more often
- Limit alcohol intake (no more than 2 drinks per day for men, no more than 1 drink per day for women), or avoid it completely if it’s a particular risk to your health
- Practice stress reduction techniques. Here’s a great resource I recently participated in
- Get regular physical activity, as recommended by your healthcare provider
- Make sure you get enough sleep
- If you think your diet is deficient in any way, please consult with a health professional such as a medical doctor or registered dietitian who can help tailor an eating plan based on your individual nutritional needs
And now on to you: which are some healthy habits you practice that help keep your immune system healthy? Are there any new ones you’d like to try? Sound off any questions or comments below in the comments section!
Hi! I’m Melissa, Registered Dietitian and mother of two dragons. When I’m not talking nutrition you can find me rolling around the floor with my kids, sewing, crafting, cooking or missing the 90s (seriously, music just isn’t the same). Read More…