In addition, research has shown that supplementing with certain vitamins, minerals, herbs, and other substances can improve immune response and potentially protect against illness.

However, it's important to note that no supplement will cure or prevent disease.

With the 2019 coronavirus COVID-19 pandemic, it's especially important to understand that no supplement, diet, or other lifestyle modification other than social distancing and proper hygiene practices can protect you from COVID-19.

Currently, no research supports the use of any supplement to protect against COVID-19 specifically.

Instead, this article provides information on well-researched supplements that may bolster immune system defenses in general.

Note that there are many types of coronaviruses, some of which, like the common cold, cause only minor symptoms — unlike COVID-19, which often results in serious, sometimes fatal symptoms.

Here are 15 supplements that are known for their immune-boosting potential.

1. Vitamin D

Vitamin D is a fat soluble nutrient essential to the health and functioning of your immune system.

Vitamin D enhances the pathogen fighting effects of monocytes and macrophages — white blood cells that are important parts of your immune defense — and decreases inflammation, which helps promote immune response.

Many people are deficient in this important vitamin, which may negatively affect immune function. In fact, low vitamin D levels are associated with an increased risk of upper respiratory tract infections, including influenza and allergic asthma.

Some studies show that supplementing with vitamin D may improve immune response. In fact, recent research suggests that taking this vitamin may protect against respiratory tract infections.

In a 2019 review of randomized control studies in 11,321 people, supplementing with vitamin D significantly decreased the risk of respiratory infections in people deficient in this vitamin and lowered infection risk in those with adequate vitamin D levels.

This suggests an overall protective effect.

Other studies note that vitamin D supplements may improve response to antiviral treatments in people with certain infections, including hepatitis C and HIV.

Depending on blood levels, anywhere between 1,000 and 4,000 IU of supplemental vitamin D per day is sufficient for most people, though those with more serious deficiencies often require much higher doses.

Summary

Vitamin D is essential for immune function. Healthy levels of this vitamin may help lower your risk of respiratory infections.

2. Zinc 

Zinc is a mineral that's commonly added to supplements and other healthcare products like lozenges that are meant to boost your immune system. This is because zinc is essential for immune system function.

Zinc is needed for immune cell development and communication and plays an important role in inflammatory response.

A deficiency in this nutrient significantly affects your immune system's ability to function properly, resulting in an increased risk of infection and disease, including pneumonia.

Zinc deficiency affects around 2 billion people worldwide and is very common in older adults. In fact, up to 30% of older adults are considered deficient in this nutrient.

Numerous studies reveal that zinc supplements may protect against respiratory tract infections like the common cold.

What's more, supplementing with zinc may be beneficial for those who are already sick.

In a 2019 study in 64 hospitalized children with acute lower respiratory tract infections (ALRIs), taking 30 mg of zinc per day decreased the total duration of infection and the duration of the hospital stay by an average of 2 days, compared with a placebo group.

Supplemental zinc may also help reduce the duration of the common cold.

Taking zinc long term is typically safe for healthy adults, as long as the daily dose is under the set upper limit of 40 mg of elemental zinc.

Excessive doses may interfere with copper absorption, which could increase your infection risk.

Summary

Supplementing with zinc may help protect against respiratory tract infections and reduce the duration of these infections.

3. Vitamin C 

Vitamin C is perhaps the most popular supplement taken to protect against infection due to its important role in immune health.

This vitamin supports the function of various immune cells and enhances their ability to protect against infection. It's also necessary for cellular death, which helps keep your immune system healthy by clearing out old cells and replacing them with new ones.

Vitamin C also functions as a powerful antioxidant, protecting against damage induced by oxidative stress, which occurs with the accumulation of reactive molecules known as free radicals.

Oxidative stress can negatively affect immune health and is linked to numerous diseases.

Supplementing with vitamin C has been shown to reduce the duration and severity of upper respiratory tract infections, including the common cold.

A large review of 29 studies in 11,306 people demonstrated that regularly supplementing with vitamin C at an average dose of 1–2 grams per day reduced the duration of colds by 8% in adults and 14% in children.

Interestingly, the review also demonstrated that regularly taking vitamin C supplements reduced common cold occurrence in individuals under high physical stress, including marathon runners and soldiers, by up to 50%.

Additionally, high dose intravenous vitamin C treatment has been shown to significantly improve symptoms in people with severe infections, including sepsis and acute respiratory distress syndrome (ARDS) resulting from viral infections.

These results confirm that vitamin C supplements may significantly affect immune health, especially in those who don't get enough of the vitamin through their diet.

The upper limit for vitamin C is 2,000 mg. Supplemental daily doses typically range between 250 and 1,000 mg.

Summary

Vitamin C is vital for immune health. Supplementing with this nutrient may reduce the duration and severity of upper respiratory tract infections, including the common cold.

4. Elderberry 

Black elderberry (Sambucus nigra), which has long been used to treat infections, is being researched for its effects on immune health.

In test-tube studies, elderberry extract demonstrates potent antibacterial and antiviral potential against bacterial pathogens responsible for upper respiratory tract infections and strains of influenza virus,

What's more, it has been shown to enhance immune system response and may help shorten the duration and severity of colds, as well as reduce symptoms related to viral infections.

A review of 4 randomized control studies in 180 people found that elderberry supplements significantly reduced upper respiratory symptoms caused by viral infections.

An older, 5-day study from 2004 demonstrated that people with the flu who supplemented with 1 tablespoon (15 mL) of elderberry syrup 4 times a day experienced symptom relief 4 days earlier than those who didn't take the syrup — and were also less reliant on medication.

However, this study is outdated and was sponsored by the elderberry syrup manufacturer, which may have skewed results.

Elderberry supplements are most often sold in liquid or capsule form.

Summary

Taking elderberry supplements may reduce upper respiratory symptoms caused by viral infections and help alleviate flu symptoms. However, more research is needed.

5. Medicinal Mushrooms 

Medicinal mushrooms have been used since ancient times to prevent and treat infection and disease. Many types of medicinal mushrooms have been studied for their immune-boosting potential.

Over 270 recognized species of medicinal mushrooms are known to have immune-enhancing properties.

Cordyceps, lion's mane, maitake, shitake, reishi, and turkey tail are all types that have been shown to benefit immune health.

Some research demonstrates that supplementing with specific types of medicinal mushrooms may enhance immune health in several ways and reduce symptoms of certain conditions, including asthma and lung infections.

For example, a study in mice with tuberculosis, a serious bacterial disease, found that treatment with cordyceps significantly reduced bacterial load in the lungs, enhanced immune response, and reduced inflammation, compared with a placebo group.

In a randomized, 8-week study in 79 adults, supplementing with 1.68 grams of cordyceps mycelium culture extract led to a significant 38% increase in the activity of natural killer (NK) cells, a type of white blood cell that protects against infection.

Turkey tail is another medicinal mushroom that has powerful effects on immune health. Research in humans indicates that turkey tail may enhance immune response, especially in people with certain types of cancer.

Many other medicinal mushrooms have been studied for their beneficial effects on immune health as well. Medicinal mushroom products can be found in the form of tinctures, teas, and supplements.

Summary

Many types of medicinal mushrooms, including cordyceps and turkey tail, may offer immune-enhancing and antibacterial effects.

6–15. Other Supplements With Immune-Boosting Potential 

Aside from the items listed above, there are many supplements that may help improve immune response:

1. Astragalus. Astragalus is an herb commonly used in Traditional Chinese Medicine (TCM). Animal research suggests that its extract may significantly improve immune-related responses.
2. Selenium. Selenium is a mineral that's essential for immune health. Animal research demonstrates that selenium supplements may enhance antiviral defense against influenza strains, including H1N.
3. Garlic. Garlic has powerful anti-inflammatory and antiviral properties. It has been shown to enhance immune health by stimulating protective white blood cells like NK cells and macrophages. However, human research is limited.
4. Andrographis. This herb contains andrographolide, a terpenoid compound found to have antiviral effects against respiratory disease-causing viruses, including enterovirus D68 and influenza A.
5. Licorice. Licorice contains many substances, including glycyrrhizin, that may help protect against viral infections. According to test-tube research, glycyrrhizin exhibits antiviral activity against severe acute respiratory syndrome-related coronavirus (SARS-CoV).
6. Pelargonium sidoides. Some human research supports the use of this plant's extract for alleviating symptoms of acute viral respiratory infections, including the common cold and bronchitis. Still, results are mixed and more research is needed.
7. B complex vitamins. B vitamins, including B12 and B6, are important for healthy immune response. Yet, many adults are deficient in them, which may negatively affect immune health.
8. Curcumin. Curcumin is the main active compound in turmeric. It has powerful anti-inflammatory properties, and animal studies indicate that it may help improve immune function.
9. Echinacea. Echinacea is a genus of plants in the daisy family. Certain species have been shown to improve immune health and may have antiviral effects against several respiratory viruses, including respiratory syncytial virus and rhinoviruses.
10. Propolis. Propolis is a resin-like material produced by honeybees for use as a sealant in hives. Though it has impressive immune-enhancing effects and may have antiviral properties as well, more human research is needed.

According to results from scientific research, the supplements listed above may offer immune-boosting properties.

However, keep in mind that many of these supplements' potential effects on immune health have not been thoroughly tested in humans, highlighting the need for future studies.

Summary

Astragalus, garlic, curcumin, and echinacea are just some of the supplements that may offer immune-boosting properties. Still, they have not been thoroughly tested in humans, and more research is needed.

The Bottom Line

Many supplements on the market may help improve immune health. Zinc, elderberry, and vitamins C and D are just some of the substances that have been researched for their immune-enhancing potential.

However, although these supplements may offer a small benefit for immune health, they should not and cannot be used as a replacement for a healthy lifestyle.

Maintaining a balanced diet, getting enough sleep, engaging in regular physical activity, and not smoking are some of the most important ways to help keep your immune system healthy and reduce your chances of infection and disease.

Moreover, remember that there is no scientific evidence to suggest that any of them can protect against COVID-19 — even though some of them may have antiviral properties.