9 Foods That Strengthen Immunity — And 3 That Can Weaken It

Your immune system acts as your body's primary defense, fending off viruses and bacteria, aiding in recovery after illness, and even minimizing the impact of sickness. That’s why it's crucial to give your immune system extra attention, especially when illnesses are circulating in your home or community.

Nourishing your immune system with the right foods is one of the most effective ways to bolster its strength. Foods rich in essential nutrients play a pivotal role in maintaining immune health. While it’s important to eat these foods when you're feeling unwell, it's equally beneficial, if not more so, when you're healthy to ensure your immune system stays strong and ready for battle.

Discover these nine immune-boosting foods that provide vital nutrients, along with three foods you should avoid to keep your immune system performing at its best.

Foods That Can Help Strengthen the Immune System

1. Broccoli

Packed with vitamin C and beta-carotene, broccoli also contains sulfur compounds that research suggests may enhance the production of glutathione, a powerful antioxidant. In terms of immune support, glutathione helps neutralize free radicals, reducing potential harm and allowing the immune system to focus on staying strong rather than repairing damage. Other cruciferous vegetables, like cauliflower, bok choy, and kale, also contain these beneficial sulfur compounds and emit a slight odor when cooked.

2. Fortified Orange Juice

I'm generally not a fan of drinking fruit instead of eating it, but fortified orange juice is hard to beat when it comes to boosting immunity. Just one cup provides 100% of your daily recommended vitamin C, an antioxidant vital for immune health, plus 25% of your daily vitamin D. This is crucial, as many people have lower-than-optimal vitamin D levels, which can make them more vulnerable to illness. A 2017 study even indicates that supplementing with vitamin D may help prevent respiratory infections.

3. Eggs

Getting enough protein is essential for immune function, and eggs are an excellent source. They also provide important nutrients such as vitamin D, zinc, selenium, and vitamin E, all of which are crucial for proper immune support. If possible, choose eggs from chickens fed a vegetarian diet for slightly higher levels of omega-3s and vitamins D and E. There's no need to opt for organic or cage-free eggs, as these don’t impact nutrient content significantly.

Read More: All About Eggs: Grades, Safety, Nutrition & More

4. Bell Peppers

Citrus fruits are great sources of vitamin C, but if you're looking to get an even bigger boost, go for a red or yellow bell pepper. A medium red bell pepper contains more than twice the vitamin C of a medium orange. In addition, bell peppers are rich in the antioxidant beta-carotene and also provide a small amount of vitamin E. Add slices to a salad, stir-fry with other veggies, or dip them in hummus instead of pita bread.

5. Lean Beef

You might be surprised to see beef on this list, but here's why it's a great choice for immune health: a 4-ounce serving of flank steak offers more than half of the Recommended Dietary Allowance (RDA) for zinc, selenium, and vitamin B6. These nutrients are essential, and even a mild deficiency can hinder immune function, making you more prone to illness. Incorporate lean beef cuts like sirloin, round steak, or flank steak into your meals up to three times a week.

6. Spinach

Vitamin A plays a key role in supporting immune function, and leafy greens like spinach are packed with beta-carotene, a form of vitamin A that also acts as an antioxidant. Furthermore, leafy greens are rich in folate, and some studies suggest that a lack of folate can weaken the immune response. If spinach isn’t your favorite, other dark-green and orange vegetables are good sources of beta-carotene, and folate can also be found in fruits, beans, nuts, and whole or fortified grains.

7. Salmon

Salmon may not immediately come to mind when you think of immune-boosting foods, but it's packed with omega-3 fatty acids, especially DHA and EPA, which are critical for reducing inflammation. By controlling inflammation, omega-3s allow the immune system to concentrate on defending the body from harmful pathogens and fighting off illness. Looking for a convenient option? Keep canned salmon or light tuna in your pantry. Both are also rich in vitamin D and selenium, which further support immune health.

8. Yogurt

Opting for yogurt with minimal added sugar and live, active cultures is an excellent way to bolster your immune system. The benefits come from the probiotics, or beneficial bacteria, as research shows that the microbiome and immune system collaborate to combat pathogens and regulate immune responses. An imbalance in good bacteria could impair immune function. Include yogurt and other probiotic-rich foods in your diet to support your microbiome, improve gut health, and enhance immune defense.

9. Chicken Soup

It might seem unlikely that chicken soup has much of an impact on your health, but perhaps our grandmothers were onto something. Research suggests that chicken soup can have a mild anti-inflammatory effect on white blood cells, which may reduce the risk of respiratory infections. Some studies even propose that a compound found in chicken may help block viral infections. While the immune-boosting effects of chicken soup are still debated, there's no harm in enjoying a bowl. In fact, it may provide more benefits than other hot liquids thanks to its protein, garlic, and onions. Plus, making a big batch is a time-saver and great for when you're working from home.

Foods That Can Weaken Your Immune System

Certain foods can hinder your immune system's ability to function at its best. Here are three foods to limit or avoid in order to minimize their negative effects on your health.

1. Caffeinated Beverages

Not getting enough high-quality sleep can weaken your immune system, making you more prone to illness and reducing your ability to fight off infections. Even if caffeine doesn’t keep you awake, consuming more than three caffeinated drinks a day can prevent your body from entering the deeper, restorative phases of sleep. To minimize this, limit caffeine intake to two or three drinks per day, and try to consume them earlier in the day.

2. Processed Foods With Added Sugars

Many packaged, ready-to-cook foods are loaded with chemicals and additives such as artificial colors, flavors, preservatives, and added sugars, which help extend shelf life and improve taste. These ingredients can irritate the body and exacerbate inflammation, which in turn disrupts immune function and weakens the body’s ability to fight off illness. Stick with whole, minimally processed foods whenever possible, and aim to avoid foods with excess added sugars.

3. Alcohol

Research shows that drinking alcohol beyond moderate levels (more than one drink per day for women, more than two for men) can significantly impair the body's immune response, increasing the risk of illnesses like pneumonia and other respiratory infections. While moderate drinking may offer some heart and anti-inflammatory benefits, the key to enjoying alcohol while protecting your immune system is to stay within the moderation guidelines—or avoid it altogether.

Carolyn Williams, PhD, RD, is the author of the cookbook 'Meals That Heal: 100+ Everyday Anti-Inflammatory Recipes in 30 Minutes or Less' and a culinary nutrition expert known for her ability to simplify food and nutrition information. A recipient of the 2017 James Beard Journalism Award, her work is featured on various websites including Cooking Light, Real Simple, Parents, Health, EatingWell, Dinogo, MyFitnessPal, eMeals, Rally Health, and the American Heart Association. You can follow her on Instagram @realfoodreallife_rd or visit carolynwilliamsrd.com.