Updated: Feb 1, 2022
Fact Sheet for Consumers
What is COVID-19?
COVID-19 (coronavirus disease of 2019) was first identified in late 2019. This disease is caused by the novel (new) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
People with COVID-19 commonly develop a cough, fever, fatigue (extreme tiredness), headache, muscle aches and pain, and diarrhea. The signs and symptoms vary widely from person to person. Some people with COVID-19 become very sick about a week after symptoms start. They could have trouble breathing and develop pneumonia. Their kidneys, liver, or lungs might stop functioning, and they might die. Some people also develop a chronic (long term) condition called long COVID. The symptoms of long COVID include fatigue, muscle weakness, sleep difficulties, and trouble thinking clearly and remembering.
COVID-19 spreads very easily from person to person, especially when people are closer than 6 feet apart. People who are infected but do not have symptoms can also spread the virus to others. When an infected person talks or coughs, tiny droplets spread COVID-19 in the air. These droplets can be breathed in by other people or land in their eyes, nose, or mouth.
How does your immune system respond to COVID-19?
If you’re exposed to COVID-19, your body’s immune system will try to fight off the disease. Your immune system is made up of cells, tissues, and organs that help fight germs that cause infections and other diseases. For example, your skin helps prevent germs from getting inside your body. Cells that line your digestive tract help protect against harmful bacteria, viruses, and other disease-causing germs. White blood cells try to destroy substances they recognize as foreign to your body. Some white blood cells also recognize germs they have encountered before and develop antibodies to defend against them in the future. If you had mumps as a child, for example, your immune system developed antibodies against the virus that caused it, and if you’re exposed to mumps again, you won’t get sick.
Your immune system also responds to germs by causing inflammation—redness, swelling, and heat—that helps kill the germs and enables your body to heal. But inflammation can also cause damage. Some people with COVID-19 have lung damage caused by inflammation. Other people experience a severe immune response (known as a cytokine storm) that is very serious and increases the risk of death. Medical treatment to reduce inflammation in patients with COVID-19 is important.
Vaccines teach your immune system how to fight off germs that cause disease. When you get vaccinated for a particular germ, your white blood cells develop antibodies to that germ. If you’re exposed to it again, your antibodies will recognize and destroy it. Common vaccines include those to prevent polio, whooping cough, and tetanus. Some vaccines need to be given more than once. You need a flu shot every year and a tetanus booster every 10 years, for example. COVID-19 vaccines are available for anyone aged 12 years or older.
What do we know about specific dietary supplement ingredients and COVID-19?
Research hasn’t clearly shown that any dietary supplement helps prevent COVID-19 or can decrease the severity of COVID-19 symptoms. Only vaccines and medications can prevent COVID-19 and treat its symptoms.
Your immune system needs certain vitamins and minerals to work properly. These include vitamin C, vitamin D, and zinc. Herbal supplements, probiotics, and other dietary supplement ingredients might also affect immunity and inflammation.
You might wonder whether taking certain dietary supplements can help your immune system work better or make you less likely to get sick or die of COVID-19. Scientists are looking at how some dietary supplement ingredients might affect the body’s ability to fight infections, viruses, and other diseases. The results so far do not show that any are useful for COVID-19.
This fact sheet summarizes what we know about the safety and effectiveness of some of these dietary supplement ingredients. They are listed in alphabetical order.
Andrographis is an herb native to Southeast Asia. It might help fight viruses, reduce inflammation, and stimulate the immune system.
Does it work? Andrographis might make respiratory tract infections less severe. A few small studies in Thailand suggest that andrographis might help relieve minor to moderate symptoms of COVID-19, such as cough, but more research is needed. One clinical trial is underway to see whether andrographis helps reduce symptoms in people who have COVID-19, but results are not yet available.
Is it safe? Side effects of andrographis include nausea, vomiting, dizziness, skin rashes, diarrhea, and fatigue. Do not take andrographis if you are pregnant or if you and your partner plan to have a baby.
Echinacea is an herb that grows in North America and Europe. It might act as an antioxidant and help stop the growth or spread of some types of viruses and other germs. It might also activate the immune system and reduce inflammation. Echinacea has been studied mainly for its effect on colds and other respiratory tract infections.
Does it work? Echinacea might slightly reduce the risk of getting the common cold, but it hasn’t been studied for COVID-19.
Is it safe? Side effects of echinacea can include gastrointestinal (digestive or stomach) upset and skin rashes. Do not take echinacea if you are pregnant.
Elderberry is the fruit of a tree that grows in North America, Europe, and parts of Africa and Asia. Elderberry might act as an antioxidant, reduce inflammation, and help fight viruses and other germs. It might also stimulate the immune system.
Does it work? Elderberry might help relieve symptoms of the common cold and flu, but it hasn’t been studied for COVID-19.
Is it safe? Elderberry flowers and ripe fruit appear to be safe to eat. However, the bark, leaves, seeds, raw fruit, and unripe elderberry fruit can be poisonous and can cause nausea, vomiting, diarrhea, and dehydration. Elderberry might also affect insulin and blood sugar levels. Do not use elderberry supplements if you are pregnant.
Ginseng (Panax ginseng or Panax quinquefolius) is a plant used in traditional Chinese medicine. It might stimulate the immune system, reduce inflammation, and help the body fight viruses.
Does it work?
It’s not clear whether ginseng helps to protect against the common cold, flu, or other upper respiratory tract infections. Ginseng has not been studied for COVID-19. One clinical trial is looking at ginseng as part of traditional Chinese medicine in people with COVID-19, but results are not yet available.
Is it safe? Side effects of ginseng can include headache, trouble sleeping, and digestive upset. High doses (more than 2.5 g/day) of ginseng might cause insomnia, rapid heartbeat, high blood pressure, and nervousness.
Melatonin is a hormone that helps regulate your sleep–wake cycle. It might also increase immune function, act as an antioxidant, and reduce inflammation.
Does it work? One study found that people who reported taking melatonin supplements were less likely than others to get COVID-19. Several clinical trials are underway to see whether melatonin helps reduce symptoms in people who have COVID-19, but results are not yet available.
Is it safe? Melatonin appears to be safe for short-term use at doses up to 10 mg/day. High blood levels of melatonin might cause delayed puberty and lower testosterone and sperm levels. Do not take melatonin if you are pregnant or breastfeeding.
N-acetylcysteine (NAC) acts as an antioxidant and helps reduce mucus in the respiratory tract (mouth, nose, throat, and lungs). NAC might also increase immune function, help fight viruses, and reduce inflammation.
Does it work? NAC might help reduce the symptoms of bronchitis, chronic obstructive pulmonary disease, and similar disorders that affect breathing. Several clinical trials are looking at whether NAC supplements help reduce symptoms in people who have COVID-19, but results are not yet available.
Is it safe? Side effects of NAC can include nausea, vomiting, abdominal pain, diarrhea, indigestion, and heartburn.
Omega-3 fatty acids
Omega-3s are polyunsaturated fatty acids found in fatty fish and fish oils. They’re also found in plant oils, such as flaxseed, soybean, and canola oils. Omega-3s are important for healthy cell membranes and proper function of the heart, lungs, immune system, and endocrine system.
Do they work? One study found that people who reported taking omega-3 supplements were less likely than others to get COVID-19. Another study found that omega-3 supplements improved survival rates in patients in the hospital with COVID-19, but more research is needed.
Several other clinical trials are underway to see whether omega-3s help reduce the risk of COVID-19 or help reduce symptoms in people who have COVID-19, but results are not yet available.
Are they safe? Omega-3 supplements are safe at doses up to about 5 g/day. Side effects include a bad taste in the mouth, bad breath, heartburn, nausea, digestive discomfort, diarrhea, headache, and smelly sweat.
For more information, read our fact sheet on omega-3 fatty acids.
Probiotics are live microorganisms (bacteria and yeasts) that provide health benefits. They are naturally present in some fermented foods, added to some food products, and available as dietary supplements. Probiotics might increase immune function and might help fight viruses.
Do they work? Probiotics might help protect against some respiratory tract infections. One study found that people who reported taking probiotic supplements were less likely to get COVID-19. Another study found that a probiotic containing the bacteria Streptococcus, Lactobacillus, and Bifidobacterium (combined with medications) reduced symptoms in patients with COVID-19, but more research is needed.
Several other clinical trials are underway to see whether probiotics help reduce the risk of COVID-19 or help reduce symptoms in people who have COVID-19, but results are not yet available.
Are they safe? Probiotics are safe for most people. Side effects can include gas and other digestive symptoms. In people who are very ill or have immune system problems, probiotics might cause severe illness.
For more information, read our fact sheet on probiotics.
The Recommended Dietary Allowance (RDA) ranges from 15 to 115 mg for infants and children (depending on age) and from 75 to 120 mg for nonsmoking adults. People who smoke need 35 mg more than the RDA per day.
Does it work? Vitamin C might help reduce the number of days the common cold lasts and lessen symptoms. It might also help reduce the risk of getting a cold in people who undergo extreme physical stress, such as marathon runners.
It’s not clear whether vitamin C helps fight COVID-19. In a clinical trial, daily supplementation with 8,000 mg vitamin C, 50 mg zinc, or both for 10 days in people with COVID-19 did not shorten the number of days people had symptoms.
Several other clinical trials are underway to see whether vitamin C helps reduce the risk of COVID-19 or helps reduce symptoms in people who have COVID-19, but results are not yet available.
Is it safe? Vitamin C is safe at intakes up to 400 to 1,800 mg/day for children (depending on age) and up to 2,000 mg/day for adults. Higher intakes can cause diarrhea, nausea, and abdominal cramps, and might also cause false readings on blood sugar monitors. In people with hemochromatosis (an iron overload disorder), high vitamin C intakes might cause iron build-up in the body, which can damage body tissues.
For more information, read our fact sheet on vitamin C.
Vitamin D is an essential nutrient that is naturally present in fatty fish and fish liver oils, and in small amounts in beef liver, egg yolks, and cheese. It’s also added to some foods, such as fortified milk. Your body can also make vitamin D from sun exposure. Vitamin D is important for healthy bones and immune function.
Does it work? Vitamin D might help protect against some respiratory tract infections, especially in people with low vitamin D levels. It’s not clear whether vitamin D helps fight COVID-19. Some studies link low vitamin D levels with a higher risk of COVID-19 and more severe disease, but others do not.
In a clinical trial, hospitalized patients with moderate to severe COVID-19 who were given a single oral dose of 5,000 mcg (200,000 IU) vitamin D did not have a shorter hospital stay or lower risk of death, even those who were vitamin D deficient when they were admitted.
Several other clinical trials are underway to see whether vitamin D helps reduce the risk of COVID-19 or helps reduce symptoms in people who have COVID-19, but results are not yet available.
Is it safe? Vitamin D is safe at daily intakes up to 25 to 100 mcg (1,000 to 4,000 IU) for children (depending on age) and up to 100 mcg (4,000 IU) for adults. Higher intakes can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones. Extremely high doses can cause kidney failure, damaged blood vessels and heart valves, heart rhythm problems, and death.
For more information, read our fact sheet on vitamin D.
Zinc is an essential nutrient found in seafood, meat, beans, nuts, whole grains, and dairy products. It’s important for a healthy immune system, making proteins and DNA, healing wounds, and the senses of taste and smell.
The RDA ranges from 2 to 3 mg for infants and children (depending on age) and from 8 to 12 mg for adults.
Does it work? Zinc lozenges might help shorten the number of days the common cold lasts. It’s not clear whether zinc helps protect against COVID-19. In a clinical trial, people who had COVID-19 but were not in the hospital took 50 mg zinc, 8,000 mg vitamin C, or both for 10 days. The supplements did not shorten the number of days people had symptoms.
Fact Sheet for Consumers----ffrials are underw ay to see whether zinc helps reduce the risk of COVID-19 or helps reduce symptoms in people who have COVID-19, but results are not yet available.
Is it safe? Zinc is safe at daily intakes up to 4 to 34 mg for infants and children (depending on age) and up to 40 mg for adults. Higher intakes can cause nausea, vomiting, loss of appetite, abdominal cramps, diarrhea, and headaches. High intakes of zinc over a long time can cause decreased immune function and low blood levels of copper.
For more information, read our fact sheet on zinc.
This fact sheet by the Office of Dietary Supplements (ODS) provides information that should not take the place of medical advice. We encourage you to talk to your healthcare providers (doctor, registered dietitian, pharmacist, etc.) about your interest in, questions about, or use of dietary supplements and what may be best for your overall health. Any mention in this publication of a specific product or service, or recommendation from an organization or professional society, does not represent an endorsement by ODS of that product, service, or expert advice.