Like everything else in our bodies, the immune system depends on nutrients to function properly. Mounting evidence from Friedman School of Nutrition Science and Policy researchers suggests that getting adequate amounts of certain nutrients may help optimize immune function, including improving resistance to infection. Here is what we know so far:

Vitamin E is an antioxidant that protects cells, including immune cells, from oxidative damage. Evidence suggests vitamin E supports optimal immune function. While vitamin E supplementation can increase risk for bleeding and stroke, dietary intake is perfectly safe.

Vitamin E is found naturally in foods like plant oils (especially sunflower, safflower, and wheat germ oil), nuts, and seeds. This vitamin is sometimes added to processed foods like breakfast cereals (check Nutrition Facts labels). Green vegetables, such as spinach and broccoli, also provide some vitamin E.

Vitamin D receptors are found in most immune cells. Adequate vitamin D levels may help maintain the body’s defense against infection.

The human body synthesizes vitamin D when the skin is exposed to sunlight. Milk provides most of the dietary vitamin D in the U.S. We also get vitamin D from other fortified foods (like some breakfast cereals and plant-based milk alternatives) and fatty fish (such as salmon, tuna, and mackerel).

Results of studies examining the effects of vitamin D supplementation on infectious disease vary significantly, and we cannot state equivocally whether vitamin D supplementation is helpful in fighting infection. Overall, studies of vitamin D supplements and health outcomes have been disappointingly negative. It is best to rely on your healthcare provider to tell you if vitamin D supplements are right for you.

Zinc deficiency and zinc overload can both impair immune function. Studies in humans testing zinc supplementation to enhance immune response have not shown any clear benefit. Additionally, supplement use increases risk of overdoing it. But it’s extremely difficult to overload on this micronutrient through diet. Oysters are the best dietary source of zinc, but poultry, crab, lobster, red meat, and fortified breakfast cereals are good sources. We also get some zinc from beans, nuts, whole grains, and dairy products.

Probiotics support a healthy gut microbiome, which plays an important role in the body’s immune response. Several randomized, controlled trials found that older adult participants receiving milk fermented with live bacteria didn’t get fewer gastrointestinal or respiratory infections, but they recovered more quickly compared to those in the control group.

Although research on probiotics and the immune system has yielded some promising results, there are many types of probiotics and the potential value of each with respect to health outcomes has yet to be sorted out. While scientists work to gain a better understanding of probiotics and immunity, consider including yogurt with live cultures, kefir, kombucha, tempeh, and some cheeses in your diet. Sauerkraut, pickles, miso, and kimchi also contain probiotics, but they are very high in sodium.

The study of nutritional immunology is helping scientists identify the role specific nutrients and bioactive compounds play in supporting a strong immune system. While some nutrients and probiotics play a role in immune function, current data do not support recommendations for supplementation. Increasing dietary intake of these food components, however, can certainly do no harm. Food sources for these nutrients (such as plant oils, nuts, seeds, seafood, milk, yogurt, poultry, beans, and whole grains) are part of a high-quality dietary pattern. The best way to support a healthy immune system, therefore, is to eat a healthy diet.

Take Charge

Try these tips to support a healthy immune system:

• Shift to plant fats: Use plant oils, nuts, and seeds in place of animal fats to assure an adequate vitamin E intake.
• Do dairy: Fluid milk is the number one source of dietary vitamin D in the U.S., and yogurt provides probiotics along with some zinc. If using milk substitutes, choose vitamin D-fortified products.
• Go fish: Fatty fish provide vitamins D and E, and oysters, crab, and lobster are among the best sources of zinc.
• Consider cereal: Breakfast cereals are often fortified with vitamins E and D and zinc. Choose low sugar, high-fiber, whole grain options, and check that the product is indeed fortified with these nutrients.
• Put food first: Foods are the best way to keep the body stocked with immune system- supporting nutrients. Supplements may be medically necessary in cases of malabsorption or deficiency, but only if advised by your healthcare provider.

This article originally appeared in the Tufts Health & Nutrition Letter, published each month by the Friedman School of Nutrition Science and Policy.