The Best Foods to Keep Your Immune System Strong  

Cold and flu season is here, and we’re all trying to either avoid getting sick, or heal from that pesky bug that’s been going around! For many people, that means taking supplements or certain medicines. But there’s a difference between protection and overdoing it—in fact, over-supplementation can lead to nausea, and even kidney stones. So before you bundle up and run to the drug store for a vitamin and mineral cocktail, consider if supplements are the best remedy, or if you need to head to the grocery store instead. Read on to learn about immune-boosting supplements, and the best foods to keep your immune system strong.. Hint: They’re all delicious!

The Link Between Supplements and Immune Health

However, when it comes to supplements and immune health, here’s what we know:  Many vitamins and minerals, including vitamins C and D, zinc, and selenium, are key players in supporting a healthy immune system. In fact, adequate levels of these vitamins and minerals support immune function and are associated with reduced risk of illness and shortened illness duration. Read on to determine whether you want to add in a certain food to your diet to boost your immune system, or if supplementation is an additional route you may want to explore.

Top Vitamins and Minerals for Immune Health

There are a few heavy-hitter vitamins and minerals that make a big impact on our immune health—and even better, they’re found in many common foods! Learn about the most valuable nutrients for immune health, and what you can eat to ensure adequate levels.

Vitamin C 

With antioxidant, antimicrobial, and antiviral properties that support a strong immune system, vitamin C can help to reduce the intensity and duration of severe colds. Start by making foods high in Vitamin C staples of your wintertime diet, especially red pepper, kale, broccoli, kiwi, citrus fruits, and berries. A few things to note:

• Vitamin C content is similar in both fresh and frozen produce;  often frozen products may retain more vitamin C than fresh that has been stored for more than 1 week.  
• Vitamin C in foods can be reduced dramatically by heat, light, and cooking liquid. To preserve vitamin C while cooking, you can:
  • Use quick heating methods like stir-frying or blanching
  • Use as little water as possible when cooking
  • Eat raw fruits at peak ripeness 

When it comes to vitamin C supplementation, the research about reducing symptoms is mixed.  You might consider taking chewable or powder (like Emergen-C), not to exceed 1000 mg per day. Be mindful that vitamin C supplementation in excess of 2000 mg per day may cause loose bowels or diarrhea.  

Vitamin D

Adequate vitamin D levels also help keep winter woes at bay thanks to its role in lowering viral replication rates and inflammation. In fact, adequate vitamin D levels help reduce your risk of influenza and upper respiratory tract infections.  Best food sources of Vitamin D include:

• Fatty fish: Salmon (canned, smoked, cooked or sushi), trout,  sardines, halibut, swordfish, herring 
• Egg yolk
• Fortified dairy, plant-based milks and cereals. Look for at least 10% vitamin D on the nutrition label
• Mushrooms grown in light, some varieties with higher vitamin D levels are chanterelle, oyster and shiitake mushrooms. Team them with some eggs for a nutritious, vitamin D-filled meal!

If you feel that you are not eating sufficient vitamin D-rich foods, consider taking a multivitamin containing 75-100% your recommended daily intake for vitamin D. Your immune system, nervous system and emotional balance ( all connected!) require vitamin D to work best!  Note that taking high doses of  vitamin D is not recommended unless you are diagnosed with a deficiency. 

Zinc

Zinc is an essential mineral that is crucial for adequate innate immunity– your body’s first line of defense against infection. In particular, zinc supports the function of T and B immune cells, as well as phagocytes like macrophages—all immune cells involved in the body’s immune response. 

Best food sources of zinc are oysters, fortified cereals, oats, pumpkin seeds, turkey breast, shrimp, and lentils.  You may want to consider taking a multivitamin/mineral with 50-100% RDA of zinc if you do not eat these foods regularly. Be sure to always take any zinc supplement with food, otherwise it can cause nausea. There is also some evidence that zinc supplementation, especially in lozenge or syrup form, shortens cold duration (though not severity) when taken soon after symptoms start. However, results from these studies are mixed, and side effects are common. Overloading on zinc can also disrupt our metabolism of other minerals.

Selenium

Selenium is a potent antioxidant that supports the cells that destroy pathogens. Selenium deficiency is linked with increased bacterial infection risk, and more severe viral infections. Maintaining adequate levels through your diet greatly benefits immune system health. While studies have not shown a benefit of supplementation in absence of deficiency, it is rare that physicians run blood tests for selenium deficiency! Here again the recommendation is to focus on food sources, and if you do not eat selenium-rich foods, take a daily multivitamin/mineral to ensure you are getting the minimum daily requirements for this essential mineral. 

Quick tip: Eat 1 Brazil nut every day! Brazil nuts are one of the most selenium-dense foods in the world, with 6-8 nuts containing almost 1000% (yes, really!) of your daily need. Other foods high in selenium include seafood (especially yellowfin tuna), organ meats, beans, lentils, tofu, sunflower seeds, and fortified cereals.

What to Know About Supplements & Safety

There are diminishing returns when it comes to levels of these immune-boosting vitamins and minerals in the body. Taking a basic daily multivitamin/mineral may provide the minimum daily requirements and cover you if and when your food choices are lagging due to emotional stress, access to food, ability to prepare food and disruptions to your routine because of travel. Megadosing many of these vitamins and minerals may cause diarrhea, nausea, abdominal cramps, and vomiting. Some supplements may also have negative interactions with medications you’re already taking, which is why it’s important to chat with your primary care provider or RD before beginning a supplement regimen.

A few other things to be aware of:

• High vitamin C intake can cause false readings on some blood glucose monitors. 
• High vitamin D intake can lead to weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones.
• Chronic consumption of 150–450 mg/day zinc can cause reduced immune function and lower HDL levels.
• Excessive selenium intake can cause a metallic taste in the mouth, as well as hair and nail loss or brittleness.

The Bottom Line

If you can, it’s best to meet your necessary levels of immune-boosting vitamins and minerals through a balanced diet. Your registered dietitian can help you come up with strategies to make it feel easy, and to find foods that you enjoy while supporting your overall health. It not only will help you avoid negative side effects of over-supplementation, it’ll also save you money, as supplements can be pricey. 

While vitamin D deficiency is pretty common, especially during the winter, deficiency in vitamin C, zinc and selenium, are actually rare. Work with your provider to get labs done to see where you might be deficient in a certain nutrient, and whether or not supplementation may be a good option for you. 

Work with a Registered Dietitian

If you’re looking for ways to stick to a healthy eating pattern, live a more healthy lifestyle or deal with a deficiency without jumping to medication, the team of registered dietitians at Culina Health can help! We are in network with most major insurance companies, and work with you to create a plan of action on your health that fits in with your budget, lifestyle, and food preferences. Get matched with a Culina Health registered dietitian today.