The immune system is the body's defense against illness and infection. But when someone has a poor immune system, due to a disease such as cancer, they're more likely to get sick easily.
Citrus fruits and green veggies are some of our top immune-boosting foods. Credit: Fascinadora/iStock/GettyImages
However — whether you have a naturally weaker or compromised immune system — you can help build it and protect your body by optimizing your eating plan. And the best way to strengthen your immune function may be to eat a nourishing diet that packs in immune-boosting foods .
Berries appear to have immune-boosting benefits due to their polyphenol content, a type of plant antioxidant that gives blueberries and other berries like blackberries, strawberries and cranberries their vibrant color.
Polyphenols are linked to countering cell damage and interacting with our gut bacteria to reduce inflammation and enhance immune response, which can play a role in the prevention and therapy of diseases with underlining inflammatory conditions, including cancer, according to a review in the November 2018 issue of Nutrients .
While the research supporting these specific immune benefits is largely based on laboratory or animal studies, the widely-prescribed, polyphenol-rich Mediterranean Diet has been associated with reducing inflammation and improving immune function in humans, according to December 2017 article in The Journals of Gerontology .
Read more: Fresh vs. Frozen Produce: Which Is Healthier?
2. Citrus Fruits
Oranges, limes, lemons and other citrus fruits are solid sources of polyphenols — and these fruits are also a great source of vitamin C. A medium orange has 70 milligrams of this vitamin, which nearly meets the daily Recommended Dietary Allowance (RDA) of 75 milligrams for women and 90 milligrams for men.
According to the Academy of Nutrition and Dietetics , a vitamin C deficiency can impair immunity, so adding more vitamin C-rich foods to your diet may foster better immune function. In addition to citrus fruits, other natural sources of vitamin C include red and green peppers, kiwi, broccoli and Brussels sprouts.
3. Green and Orange Vegetables
Orange and dark green vegetables such as sweet potatoes, peppers, carrots, spinach and broccoli are great sources of beta-carotene, which the body converts to vitamin A. Vitamin A is another nutrient that plays an important role in the development and regulation of the immune system, according to a September 2018 review in the Journal of Clinical Medicine .
Vitamin A also helps protects the integrity of the skin and other epithelial tissues that cover body organs, as well as the mucous membranes that line the mouth, nose, bladder and lungs. These tissues and membranes protect the body by acting as a barrier to bacteria and viruses and also by trapping and destroying disease-causing germs.
While vitamin A is also found in meat, liver and milk, animal-based products tend to be high in saturated fat and cholesterol, so you'll want to limit those.
4. Nuts and Seeds
Nuts and seeds are prime sources of vitamin E, zinc and plant-based protein — three nutrients that can keep your immune system healthy and strong. Vitamin E acts as a natural antioxidant, which neutralizes free radicals and is therefore linked to improve immune function while zinc and protein help keep your immune system chugging, according to the Academy of Nutrition and Dietetics.
To get more of all three of these immune-system-bolstering nutrients in your diet, reach for walnuts, sunflower seeds, almonds, hazelnuts and peanut butter.
5. Foods for Gut Health
There are many other foods presumed to help boost immunity, however, human research trials are lacking. For instance, any strategies that keep gut bacteria thriving can potentially help immune function. And a habitual diet that emphasizes plant foods — such as a vegetarian or Mediterranean diet — is linked to gut bacteria with more health-promoting properties, according to research published in the September 2015 issue of the journal Gut .
Other foods that may help the body's immune response, according to a February 2014 review in Today's Dietitian , include foods that are sources of prebiotics and probiotics. Both interact with our gut bacteria to reduce inflammation and prevent pathogens from getting past the gut lining.
Prebiotics are a type of fiber the body can't digest and act as a nourishing food for the gut bacteria. Food sources of prebiotics include insulin, a fiber additive, along with chicory, Jerusalem artichokes and onions. Probiotics are live microorganisms that can confer health benefits and food sources include yogurt with live active cultures, kombucha, kimchi, miso and fermented milk.
Read more: 5 Probiotic-Rich Recipes Your Gut Will Love
The Importance of a Healthy Diet
It's no secret that an important way to foster immunity is to keep your body well-nourished. A diet that lacks vital nutrients — whether due to dieting or from the effects of illness — can impair your immunity, according to a June 2016 review in Trends in Immunology . According to the study authors, malnutrition is associated with chronic inflammation and recurrent infections, which are both signs of impaired immune function.
Poor nutrition negatively affects the health of gut bacteria, which play an important role in immunity, and may lead to nutrient deficiencies that can weaken your body's defenses. Specifically, inadequate protein, zinc, and vitamins A, C and E impair immune function, according to the Academy of Nutrition and Dietetics. So, a first step in improving immune health is to center your diet around nutrient-dense foods that support a healthy weight and adequate muscle mass.
Other Ways to Boost the Immune System
While eating a healthy diet may provide some immune-boosting power, there are other things you can do to foster a healthy immune system. Your immune system will benefit from not smoking, exercising regularly, limiting your alcohol intake, getting enough sleep, maintaining a healthy weight and attempting to reduce stress in your life, according to Harvard Health Publishing .
Also, you can reduce your risk of infection by washing your hands frequently and taking precautions to prevent foodborne illness , like cooking food thoroughly and storing cold foods cold and hot foods hot. If you have a suppressed immune system due to medication or a medical condition, such as cancer, ask your doctor about additional steps you can take to reduce your risk of infections and boost immunity.