Get more of these nutrients in your diet to help support a healthy immune system.

Vanessa Rissetto, M.S., R.D., C.D.E.
December 09, 2020
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It's already hard to stay motivated, active and productive—but add being sick on top of that and you can really be thrown way off your game. Thankfully, there are tons of simple changes you can make to your diet to keep your immune system healthy and support your body in fighting off unwanted infections (which is especially important in the age of COVID-19). Nutrition is important for all aspects of health, including immune health. In general, eating a well-balanced diet, staying hydrated, getting enough sleep and reducing stress in your life all help support your immune system. Some nutrients are especially important for your immune system. Here, we're highlighting five critical nutrients you need in your diet for optimal immune health. Plus, learn foods to include to get these vitamins and minerals in your diet.

1. Vitamin A

One of the earliest signs of a mild vitamin A deficiency is a decreased ability to fight off infections, especially respiratory infections like COVID-19. Vitamin A also supports and strengthens vision, reproduction, bone growth and immunity. By the way: vitamin A is an essential vitamin, which means that our bodies cannot make it on their own. For this reason, it's super important to make sure your diet is full of this immune-boosting nutrient.

The science behind vitamin A and immunity

Vitamin A strengthens both the innate and adaptive immune systems of the body. The innate immune response protects the skin, eyes, respiratory tract, gastrointestinal tract and reproductive organs. The adaptive immune system produces antibodies that attack foreign invaders (like the flu virus). Carotenoids (a type of vitamin A found in plant foods) are also powerful antioxidants that help the body fight inflammation. Like most nutrients for immune health, the best way to get your vitamin A is from food, rather than supplements.

Vitamin A supplementation is especially prone to causing toxicity, and over-supplementation can actually weaken the immune system. The good news? Food sources of vitamin A are safe and effective for meeting your daily needs. Plus, they're colorful and delicious!

The best food sources of vitamin A

There are two main dietary sources of vitamin A: carotenoids (found in plant foods) and retinoids (found in animal foods).

Retinoids

  • Beef liver
  • Herring
  • Cow's milk (fortified with vitamin A)
  • Shrimp
  • Eggs
  • Salmon

Carotenoids

  • Sweet potatoes
  • Carrots
  • Spinach
  • Kale
  • Greens: mustard greens, collard greens, turnip greens, beet greens
  • Swiss chard
  • Winter squash

2. Vitamin D

Did you know this "vitamin" is technically not a vitamin at all? Instead, vitamin D actually functions more like a hormone in your body.

Though perhaps best known for its bone health benefits, vitamin D also plays a critical role in strengthening our innate and adaptive immune responses. The powerful vitamin signals the body to create immune-boosting compounds, like antimicrobial proteins responsible for protecting the body from getting sick.

The nutrient has gained extra attention lately due to its potential association with COVID-19 risk. More research is needed before we can say that low vitamin D levels definitively raise one's risk of COVID-19 (or cause worse symptoms if one's infected). That said, current studies suggest there seems to at least be an association between vitamin D deficiency and more severe COVID-19 outcomes (learn more about vitamin D and coronavirus).

How to get enough vitamin D

Our bodies create vitamin D when we soak up UV rays from the sun. Unfortunately, there are very few food sources of vitamin D, and most people don't get enough vitamin D from the sun to meet their needs, especially in the winter. Vitamin D deficiency is very common among breastfed infants, older adults, people with limited sun exposure, people with dark skin (melanin blocks vitamin D activation), people with fat malabsorption, and people who have a BMI greater than 30 (classified as obese) or who have undergone gastric bypass surgery.

If you have access to regular sunlight, the recommendation is to get 5 to 15 minutes of sun exposure 3 to 4 days per week. Exposure in the morning or late afternoon provides a good source of vitamin D and is less damaging to the skin.

If you fall into one of the categories of people at greater risk for vitamin D deficiency or if you've been diagnosed with a deficiency, you're a good candidate for a supplement. Vitamin D is among the very few nutrients that we recommend getting from supplements, especially if you don't get much sun exposure. Most adults need 15 mcg or 600 IUs daily, although some experts recommend more than that.

The best food sources of vitamin D

Although there are very few food sources of vitamin D, you can still optimize your vitamin D intake by adding some of these foods to your diet. (Get more information with our list of top foods with vitamin D to eat.)

  • Cod liver oil
  • Salmon
  • Mackerel
  • Sardines
  • Vitamin D-fortified milk, yogurt and nondairy milk
  • Beef liver
  • Egg yolks
  • Mushrooms with UV fortification

3. Zinc

Zinc is an essential mineral that must be consumed via the diet. It's actually critical to consume zinc daily, since the body lacks the ability to store the mineral. Zinc helps support brain function, maintain healthy hormone levels, synthesize DNA and proteins, and boost the immune system. It also serves as a cofactor for some 300 enzymes in the body. What's more, zinc deficiency is associated with delayed growth, sexual dysfunction, diarrhea and delayed wound healing.

The science behind zinc and immunity

Zinc supports the functioning of immune cells like neutrophils and macrophages. As a result, a zinc deficiency can lead to a higher risk of infections. You've probably seen zinc lozenges at your pharmacy. Though the research is conflicting, the nutrient is thought to potentially drive down the duration and severity of symptoms associated with the common cold by preventing the entry of the virus into cells and stopping it from multiplying in the body.

Zinc's antiviral properties may help the body fight viral species similar to those that cause COVID-19, per emerging research. However, studies on zinc and viruses like the coronavirus are still in their infancy, and a great deal of further research in humans is still needed before we can making any sweeping conclusions ⁠about the relationship between the two.

The best food sources of zinc

  • Oysters
  • Beef
  • Crab
  • Lobster
  • Chicken
  • Pumpkin seeds
  • Yogurt
  • Cashews
  • Chickpeas

4. Vitamin C

Vitamin C gets a lot of air time around immunity—and for good reason. The essential vitamin may help fight colds, ramps up antioxidant activity in the body, and aids in the absorption of other nutrients, like iron. Vitamin C is also needed for collagen synthesis. Quick refresher: collagen is a structural protein that keeps the skin looking plump and healthy. Sign us up.

The science behind vitamin C and immunity

Research shows that a high vitamin C intake is associated with decreased risk of common chronic diseases, including cardiovascular disease, cancer and certain neurological conditions. When it comes to fighting off infections, vitamin C's immune-boosting powers are likely linked to its antioxidant properties. That is, vitamin C (which is an antioxidant itself) helps regenerate other antioxidants—like vitamin E—in the body, thereby decreasing the number of harmful free radicals that can bolster infections.

The best food sources of vitamin C

  • Citrus fruits
  • Bell peppers
  • Strawberries
  • Cantaloupe
  • Brussels sprouts
  • Broccoli
  • Tomatoes

5. Probiotics

While they aren't exactly a nutrient per se, probiotics are incredibly important for pretty much every aspect of our health. Probiotics are defined as live microorganisms that benefit the overall health of their host. Yes, we are hosts to billions of little organisms that help us survive and thrive!

There's a ton of research currently being done in the area of probiotics, and scientists predict they may even be the future of medicine. While many functions and benefits of probiotics have yet to be discovered, we do know that these microscopic bugs play a big role in strengthening our immune system. (Learn more about your gut health and coronavirus.)

The science behind probiotics and immunity

The Lactobacilli and Bifidobacteria species of probiotics are among the most well-researched microorganisms to date. These little guys are found in fermented foods like yogurt and kimchi.

Once inside the body, probiotics interact with receptors on the intestinal cells and modulate both the innate and adaptive immune responses. Probiotics also strengthen the lining of the gut, which protects the GI tract from harm by bad bugs. These good bacteria also boost immunity by decreasing inflammation in the body.

Probiotics are so powerful that they may even prevent and help treat some inflammatory bowel disorders, gastrointestinal infections and allergic responses. Just remember: the benefits of probiotics to the immune system depend on the specific strain, dose, route, and frequency of delivery.

The best food sources of probiotics

  • Yogurt
  • Kefir
  • Unpasteurized sauerkraut
  • Kimchi
  • Tempeh
  • Miso

The vast majority of people benefit from adding probiotic-rich foods to their diet; however, they are not for everyone. If you are considering taking a probiotic supplement, talk with your doctor about the specific probiotic strain and dose that is right for you.