Science or Sales

Sarah Boothman, Ph.D.
February 2026
(12 minutes)

It’s winter. It’s dark and cold outside, you’re burnt out from the holidays, and it seems that everyone around you is getting sick. You open your social media app of choice and are met with ads for supplements that can help you fight off those pesky post-holiday illnesses. You see influencers taking immunity juice shots as part of their aesthetically-pleasing morning routines, and your local CVS is running a huge sale for vitamins and supplements. There are a lot of choices out there to help you stay healthy, but how do we know what will actually work? When it comes to these “immune-boosting” supplements, what is backed by science and what is just good marketing?

To understand how these vitamins and supplements work in our bodies, we first need a general idea of how the immune system works. The immune system is a network of cells in the body that identify and kill invading microbes. There are two branches of the immune system: the innate and the adaptive systems. Innate immunity is the first line of defense against an infection. Cells within this branch are constantly circulating the body looking out for signs of pathogens. When one is identified, these cells will send out cytokines (molecular “alert signals”) to call other immune cells to the site of infection. At this point, specialized cells called phagocytes (Greek; phago = to eat, cyto = cell) engulf the pathogens and destroy them. This process is quick, but it is not specific to any one type of pathogen. By contrast, the adaptive (sometimes called acquired) immune system works slower but is targeted to specific pathogens. This branch contains cells that learn specialized patterns on pathogens and build up “memory” against them so that a quicker response can be mounted when/if these pathogens return to the body. These cells can either create antibodies against the pathogens (B cells) or they can create special receptors on their surfaces that bind only to the pathogen of interest (T cells). These antibodies and receptors then serve as tags on the surface of microbes, which lets phagocytes know that they need to be destroyed. It is important that both of the branches of the immune system work together to mount an efficient and complete response to infection in the body.

It is also important that the immune system stays balanced. A crucial part of immune responses is the ability for these cells to recognize invading pathogens, but equally critical is the ability of these cells to avoid harming healthy tissues in the body. Sometimes the cells of the adaptive immune system are flawed and end up tagging perfectly healthy cells for destruction. This is what is referred to as an autoimmune condition. There are many causes of autoimmune diseases, such as genetics, environmental triggers, and hormonal factors, and research into these conditions is still ongoing. In addition, the over-recruitment of immune cells into an area is what leads to inflammation in an area. Some level of inflammation is necessary in order to clear infection, but when it is left unchecked, damage can occur to healthy tissues. Thus, it is vital to have a healthy immune system, but it can be dangerous when over-activated. 

Most labels on immune supplements have vague claims like, “supports immune function” or “boosts immune defense,” but how do these products actually help the immune system do its job? The active ingredients in these supplements fall into three general categories: immunostimulants, antioxidants, and anti-inflammatories. 

Immunostimulants are compounds that activate the immune system, increasing the response to pathogens. Commonly used substances that fall into this category include zinc, echinacea, and ginseng. 

Zinc is a metal that has roles throughout the body and within all cells. Specifically within the immune system, zinc has been shown to be necessary for the development and specialization of immune cells (i.e. creating all the different types of cells that need to be present in a healthy immune system). Zinc also plays a role in the sending and receiving of “alert signals” by immune cells. For example, when an innate immune cell recognizes a bacterial pathogen, the cell must process this information and then send out a signal to recruit more immune cells to the infection site. Inside of this cell, zinc works with other molecules to efficiently produce that alert signal, and studies have shown that not having enough zinc breaks this process. 

Echinacea also assists in the activation of the innate immune system, but the mechanism of how this happens is largely unknown. This herbal treatment has been used for centuries among indigenous peoples, and some evidence suggests that it can help shorten the length of illnesses. Laboratory studies in mice models have shown that echinacea extracts can increase the mobility of phagocytes, meaning that immune cells can get to the site of an infection faster. 

Ginseng works in a different way to activate immune cells. Different molecules found within the ginseng root have been shown to activate cells of both the innate and adaptive immune system in laboratory settings. Additionally, when mice were fed ginseng, they produced a higher amount of antibodies. Clinical studies have revealed that adding ginseng to standard medical treatments for viral or bacterial infection can shorten the duration of illness compared to just those treatments alone. Evidence from other clinical studies in Korea suggests that ginseng can improve immune responses of patients undergoing chemotherapy. These results are encouraging, but differences in the way studies are set up and the interpretation of results have been debated in the field.

“Antioxidant” is a chemical term, but it has also become a buzzword for supplement marketing and health influencers. On a basic level, an antioxidant is a chemical compound that is able to scavenge for unstable molecules called free radicals. Within cells, free radicals are harmful, and antioxidants help reduce the amount of them, thereby protecting cells from damage. The innate immune system naturally creates free radicals as a side effect of killing microbes, so antioxidants are needed to protect normal, healthy cells (and even the immune cells themselves) from being damaged by these molecules. 

One of the most famous supplements marketed as an antioxidant for the immune system is vitamin C. Anecdotal evidence suggests that vitamin C can reduce the severity of cold and flu symptoms and may even prevent individuals from getting sick in the first place. However, it is generally accepted that vitamin C will not protect you from getting sick, and its effect on severity/longevity of infections is heavily disputed by medical studies. 

Elderberry is another popular substance used in immune support supplements that has antioxidant properties. Similar to vitamin C, studies have shown that it is able to reduce the duration and severity of symptoms, but it is not effective as a preventative treatment. Some laboratory studies also suggest that elderberry also has some anti-inflammatory effects (see below), but the results were widely inconclusive. 

In addition to activating immune cells and protecting healthy tissues, some ingredients in immune support supplements actually turn down cellular activity. While this may seem counterintuitive, it actually helps the immune system stay on track. By limiting the activation of these cells, they are more likely to focus on invading pathogens and less likely to turn on healthy tissues. Limiting the amount of active cells also decreases the risk of damaging inflammation. Thus, some immune boosters also include a few “immunosuppressive” and anti-inflammatory components. 

Vitamin D is a widely-used supplement, and it is primarily used for bone health but also has a role in immune function. Vitamin D deficiencies have been linked to autoimmune disorders for decades, indicating that a certain level of the vitamin is needed to keep the immune system in check. In line with this, there are some laboratory studies that show vitamin D decreases the activation of innate immune cells. There is also evidence showing the vitamin decreases the amount of “alert” signals released by cells, therefore decreasing cell migration and any resulting inflammation. Moreover, the current theory of how vitamin D supports the immune system has to do with balancing the amount of reactive cells and “helper” cells within both branches. For example, vitamin D has been shown to push macrophages (a type of phagocyte in the innate branch) from their activated “eating” state into their “M2” state, where they prevent inflammation and promote tissue repair. In this way, vitamin D helps balance the microbe-busting role of immunity with protection of healthy tissues in the body.

Similar to vitamin D, deficiencies of vitamin A have been linked to immune issues in humans and animal models. Vitamin A has a few documented actions within the immune system, but the most convincing evidence is for its role in “immune homeostasis” (the balance of cell types in the immune system). Like its vitamin D coworker, vitamin A has been shown to push macrophages into their anti-inflammatory M2 state. Vitamin A has also been shown to have a similar effect on cells throughout the innate and adaptive immune system, ensuring that enough pathogen-killing cells are present while keeping inflammation at bay. Some anecdotes suggest vitamin A can be therapeutic during infections such as tuberculosis, but more rigorous studies are needed to confirm this.

All in all, there is evidence that some components of immune supplements can help improve immune function. One overarching theme that can be found throughout these studies is that these treatments can help reduce the severity and duration of cold/flu symptoms, but they cannot prevent an individual from getting sick. This is a modest benefit, but what are the risks involved in using these supplements? First, as with any treatment, there is a risk of allergic reaction. Some of the ingredients in these supplements can also interact with other medications you are taking, leading to decreased efficiency and unwanted side effects. Because the FDA treats vitamins and supplements as food and not drugs, they do not monitor their quality and safety as closely as they do for pharmaceuticals. Thus, there may be low quality ingredients included in supplements that lead to undesirable side effects. For herbal and botanical treatments, the preparation of these substances can have harsh consequences. For example, elderberries contain cyanide-like compounds, and incorrect preparation of extracts and syrups can cause contamination that will make you sick. 

In addition to contaminants and low quality ingredients, there is a possibility of overdosing on certain vitamins and minerals while taking these supplements over extended periods. Some vitamins, like vitamin C, will clear out of your system safely, but others will build up in your tissues and cause damage. For instance, excess consumption of vitamin D can lead to kidney stones and heart problems. Prolonged intake of immune boosters is also cautioned for people who are already at risk for autoimmune disorders (either genetically or environmentally) as overactivating your immune cells could push you into an autoimmune state.

To help mitigate the risks associated with immune support supplements (or any supplement in general), there are steps you can take to inform yourself. In 1995, the NIH established the  Office of Dietary Supplements (ODS) to research dietary supplements and “foster knowledge” across the US. The ODS website contains helpful factsheets that outline the purpose, use, and associated risks of certain vitamins, minerals, and herbal treatments. In a similar vein, the Department of Defense has created a supplement scorecard as part of Operation Supplement Safety that helps consumers decide if a supplement is safe and beneficial to take. Finally, the best source of advice when it comes to any supplement or treatment is going to be your primary care physician.

So what are we to do when faced with winter’s impending plagues? Many experts agree that the best way to keep yourself and your immune system in fighting condition is to maintain healthy habits. Most people already get sufficient amounts of immune-supporting vitamins and compounds by eating well-balanced diets. Adequate sleep and exercise is also crucial to the proper function of the immune system. To help prevent infections, you can follow safety guidelines such as hand-washing and disinfection. Another very successful prevention tactic is to keep up-to-date with vaccinations, especially for seasonal illnesses such as the flu and COVID-19. (See the GGR article on vaccines by our fearless leader, Mary Cundiff, for more information.)

In an article by Harvard Health, Dr. JoAnn Manson puts it best by saying, “Supplements are never a substitute for a balanced, healthful diet, and they can be a distraction from healthy lifestyle practices that confer much greater benefits.” By taking the supplement shortcut to immune health, you may be missing out on other benefits that come with lifestyle changes. This is not to say that you should never take a supplement. I have been known to take an Airborne gummy when I start to feel sick, and I enjoy a nice cup of elderberry tea whenever I get a little sniffly. It is most important to be informed in your decisions about your health and be able to weigh the benefits of supplements against any risks they may have. Ask questions, wash your hands, get vaccinated, and stay safe!

*Disclaimer: This article is for informative purposes only. Individuals should always consult a physician before starting or stopping any treatment or supplement.

Sources and related readings are linked throughout the body of this article.