There may be no more important part of our body than our immune system. Through its nonstop work to prevent and limit the effects of harmful pathogens like bacteria and viruses, we’re able to maintain our health and recover from illnesses caused by these invaders. Our immune cells make up one of the most sophisticated, coordinated systems in the body—one that is essential for our survival.
With the recent outbreak of the novel coronavirus, also known as COVID-19, there has been an increased focus on the importance of keeping our immune systems running strong. As a result, there’s a lot of information being shared about the effect that food and dietary supplements might have on immune health. Some of this information is based in strong science, while some is…not so much.
In this article, we’ll address how the food we eat can support immune health, why many trendy supplements and “superfoods” don’t make the cut, and whether or not you can really “boost” your immune system through food. (Hint: the answer is no.) We want to be clear that the information provided here relates to healthy adults; the same conclusions may not apply to children, the elderly or those who are immunocompromised.
Is diet connected to immune health?
Yes! Many nutrients we get through the food we eat are essential for immune function, so eating a well-balanced, healthy diet allows your immune system to be the best version of itself. When we get sick and our immune system becomes more active, the demand for both energy and nutrients goes up, making adequate nutrition even more vital.
At the same time, for most healthy people, consuming more energy (as in, calories) or nutrients than we need won’t necessarily give any added immune benefits. Almost everything that we consume above and beyond what we need will pass through us unused. In the case of fat-soluble vitamins, it will be stored for later use, which can be harmful above a certain level. This is why dietary supplements aren’t a “magic bullet” to health promotion—just because we’re able to take in high amounts of vitamins and minerals doesn’t mean they’ll benefit us.
However, it’s a different story if a person’s diet is deficient in key immune-related nutrients. In this case, altering the diet to get more of those missing nutrients can improve immune function. A common example is vitamin D: It can be hard to get sufficient amounts through our diet because it isn’t naturally found in many foods and many people don’t have enough sun exposure to generate it. Therefore, many people don’t get enough. In this case, seeking out a supplement or foods fortified with vitamin D may be beneficial.
Here’s a quick list of nutrients known to be beneficial in supporting immune health, brief summaries of some of their roles in the immune system, and the foods in which you can find them:
Immune System Roles
Involved in immune system development; regulates immune cell production and responses to pathogens
Beef liver, sweet potato, boiled spinach, carrots, dairy products, cantaloupe
Stimulates production and function of immune cells; antioxidant capabilities
Citrus fruits and their juices, red and green peppers, broccoli, cabbage, cauliflower
Tones down the inflammatory response; assists in producing proteins important for immune cell activation
Cod liver oil, fish (rainbow trout, sockeye salmon, sardines), mushrooms, fortified milk and milk alternatives, fortified cereals
Antioxidant capabilities; involved in immune cell signaling and production of immune cells
Cooking oils, almonds, hazelnuts, peanuts and peanut butter, sunflower seeds
Omega-3 fatty acids
Component of immune cell membranes; involved in enhancing immune cell functions
Chia seeds, flaxseed and walnuts, cooking oils like flaxseed, canola and soybean, salmon, herring, sardines, mackerel, fortified foods
Involved in development and function of immune cells
Oysters, beef, crab, lobster, pork, legumes, fortified cereals, chicken, nuts, seeds, dairy
Involved in regulating inflammation and immunity; deficiency is associated with impaired production and activation of immune cells
Brazil nuts, fish (tuna, halibut, sardines), ham, shrimp, beef, poultry, grains (enriched and whole), eggs, dairy
Table source: National Institutes of Health, Office of Dietary Supplements
Supplements and “superfoods”: Can they give my immune system a “boost”?
The extremely blunt answer is: No. Nor would you necessarily want them to. Our immune systems are tightly regulated, and for good reason. When we’re attempting to fight off harmful bacteria or viruses, our bodies respond by mass-producing immune cells to overwhelm the foreign invader, which causes inflammation. While inflammation is necessary for recovery from infection, it’s also important that it resolves quickly to avoid causing unnecessary damage to the affected part of the body. If there’s no immediate infection, having an increased number of active immune cells is not a good thing. An overactive or hypersensitive immune system leads to excessive inflammation and is responsible for conditions like allergies and autoimmune diseases.
Instead, a strong immune system is prepared to respond rapidly when an infection hits. Eating a varied, healthy diet rich in nutrients is known to play a role in optimal immune function. Products being touted as “superfoods” don’t do this any better than regular old fruits, vegetables, nuts, legumes and other sources of healthy fats and protein—which are often more accessible and affordable.
But what about…
No, the elderberry syrup and protein powders that you’re seeing ads for do not have strong evidence—or often, any evidence at all—to back up their claims related to immune health. In fact, foods and dietary supplements that make claims about treating, preventing or curing illnesses should be avoided at all costs. At best, these claims are not backed by science and should not be made on supplement packaging. At worst, they could be dangerously harmful to health. It’s important to know that no food or nutrient has been shown to reduce risk for COVID-19 infection.
What can I do to support my immune system?
We know that overall good nutrition is important for maintaining optimal immune health, but there is no clear evidence that a specific food or nutrient provides a quick immune fix. Instead, eating a variety of foods, with a focus on fruits, vegetables, nuts and seafood, can provide us with many of the vitamins and minerals that play key roles in supporting the immune system. And let’s not forget the importance of non–food behaviors for maintaining a strong immune system: behaviors like frequent hand washing, maintaining a healthy weight, regular exercise, not smoking, practicing techniques for stress reduction and getting adequate sleep are all vital for ensuring that our body is properly equipped to stay as healthy as possible.
This article includes contributions from Kris Sollid, RD, and Ali Webster, PhD, RD.