Do Immunity Supplements Actually Work?
A dietitian breaks down what research says about vitamin C, oregano oil, zinc and elderberry.
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Between flu, cold, COVID and RSV, many Americans are looking for ways to help support their immune system especially through the winter season. According to the International Food Information Council’s 2025 Food and Nutrition Survey, 28 percent of Americans are seeking to improve their immune health through their diet. But in addition to diet, you may be looking to supplements to bolster your immunity. But do they really work? Here’s what research says about common immunity supplements.
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Vitamin C
Do you start taking tons of vitamin C supplements once you start feeling sick? Vitamin C does help support your immune system, and is an antioxidant that helps protects cells and fights inflammation. However, it doesn’t cure a cold — or the flu — or any other such ailment.
Studies show that if you don’t get the recommended amounts of vitamin C, you may see better immune function once you do take in enough (because your immune system will be fully armed and ready). Further, research shows that if you do have an infection, your body will need more than the recommended amount of the vitamin to support your body’s defense system, which is working harder than usual. The maximum amount of vitamin C that is safe to take daily is 2,000 milligrams. Taking too much is linked to diarrhea, stomach upset and some data suggests that taking too much for too long is linked to kidney stones in those with kidney issues.
Oregano Oil
Oregano oil is derived from the leaves of the oregano plant, and is known to have an unpleasant, bitter taste. The oil has been used for hundreds of years in the Mediterranean region primarily amongst the ancient Greeks and Romans for various ailments, including fighting infection and the common cold. Today, many people still use it to fight infections and the common cold despite its unpleasant taste. There is initial research that suggests that oregano oil may have antimicrobial, antioxidant and anti-inflammatory properties, though more research is needed. There is one small study conducted with 60 participants with upper respiratory viruses. Participants used a botanical spray that contained oregano oil and other herbal ingredients and felt better 20 minutes later. However, research is needed with oregano oil on its own to make a stronger association.
Zinc
If you think that mega-dosing on trendy products, probiotics or vitamins will help ward off colds, the flu or other such illnesses, think again. There are products that contain ingredients like zinc or elderberry, which have been touted to help cure colds, flu and the like. However, often time the ingredient added is in a sub-optimal dose that isn’t effective or proven.
For zinc, research shows mixed results for its effectiveness in staving off colds. Some studies show it does help shorten the duration of a cold, while others don’t. Researchers don’t know why the results are mixed. As such, zinc can’t be recommended to shorten a cold because there is no clear treatment plan or dosage.
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Elderberry
Small studies have also shown positive results for elderberry. A published study in the journal Nutrients found that taking elderberry extract before, during and after long-distance air travel may reduce the severity and duration of cold-like symptoms. However, the National Institute of Health’s National Center for Complementary and Integrative Health says that only preliminary research suggests that elderberry may relieve symptoms of flu, colds or other upper respiratory infections.
In addition, the U.S. Food and Drug Administration (FDA) and Federal Trade Commission (FTC) have taken action against companies that market elderberry products with unsubstantiated claims of effectiveness for COVID-19. Further, the FDA and FTC also warn, “Dietary supplements are not approved by the FDA before they are sold to the public. When public health concerns arise about the safety of a dietary supplement or an ingredient including an herb, the FDA can take action to protect the public. Manufacturers and distributors of supplements are responsible for evaluating the safety and labeling of their products before marketing to ensure that they meet all regulatory requirements.” It’s recommended to speak to a healthcare professional before taking any supplements.
Bottom Line: There is no magic cure for cold season ailments. Your best bet is to eat a well-balanced, varied diet to keep your immune system in tip-top shape before that cold or flu strikes. In addition to a good diet, having an overall healthy lifestyle with the proper amount of sleep, regular exercise and minimal stress can also play a role in keeping your immune system working at its best.
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