Dietary Supplements in the Time of COVID-19

Fact Sheet for Consumers

What is COVID-19?

COVID-19 (coronavirus disease 2019) was first identified in late 2019. This disease is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus.

Common symptoms of COVID-19 include cough, fever, headaches, muscle aches and pain, diarrhea, and extreme tiredness. The signs and symptoms can be very different from person to person. Some people with COVID-19 become very sick about a week after symptoms start. They might have trouble breathing and develop pneumonia. Their kidneys, liver, or lungs might stop working, and this could lead to death.

Some people also get a chronic (long-term) condition called long COVID. The symptoms of long COVID include shortness of breath, extreme tiredness, muscle aches and weakness, sleep difficulties, and trouble thinking clearly and remembering. These symptoms can last for weeks, months, or years. Your risk of severe disease and long COVID is lower if you have been vaccinated against COVID-19.

How does your immune system respond to COVID-19?

Your immune system is made up of cells, tissues, and organs that protect you against harmful bacteria, viruses, and other germs that cause diseases. For example, white blood cells attack substances they recognize as foreign to your body. Some white blood cells also recognize germs that they have been exposed to before and develop antibodies to defend against them in the future. If you come into contact with the SARS-CoV-2 virus, your body’s immune system will try to fight it off.

Your immune system also responds to germs by causing inflammation—redness, swelling, and heat—that helps kill the germs so your body can heal. However, inflammation can also cause damage, and this can sometimes occur in the lungs of people with COVID-19. Other people experience a severe immune response (known as a cytokine storm) that is very serious and increases the risk of death.

Vaccines teach your immune system how to fight off germs that cause disease. When you get vaccinated for a germ, your white blood cells make antibodies for that germ. If you’re exposed to it again, your antibodies will recognize the germ and destroy it. COVID-19 vaccines are available for anyone age 6 months or older.

What do we know about specific dietary supplement ingredients and COVID-19?

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. Eating a variety of nutritious foods can give you enough vitamins, minerals, and other nutrients for a healthy immune system.

Scientists are investigating how some dietary supplement ingredients might affect the body’s ability to fight infections and other diseases. This research has not clearly shown that any dietary supplement helps prevent or treat COVID-19. This fact sheet summarizes the results of this research and lists dietary supplement ingredients in alphabetical order. We also include information about how these ingredients might interact with common medications.

The health professional version of this fact sheet includes more details and references to the scientific literature.

Andrographis

Andrographis is an herb that is 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 mild to moderate symptoms of COVID-19, but other studies do not. For example, in one study of people with mild to moderate COVID-19, half the patients took andrographis combined with an antiviral medication and the other half took the antiviral alone to see whether adding andrographis could help prevent the disease from progressing to severe COVID-19. However, patients in both groups developed severe disease at about the same rate.

In another study of people who were hospitalized with mild to moderate COVID-19, those who took andrographis plus another herb called Eleutherococcus senticosus had a lower risk of becoming severely ill. Also, some of their symptoms, including sore throat and muscle pain, were milder, but other symptoms, including cough and fever, were not. In another study, people who were hospitalized with mild COVID-19 and who took andrographis did not have a lower risk of pneumonia.

Is it safe?

Side effects of andrographis include nausea, vomiting, dizziness, skin rashes, diarrhea, and extreme tiredness.

Andrographis might interact with blood thinners and blood pressure medications because it might disrupt blood clotting and decrease blood pressure. Andrographis might also decrease the effectiveness of medications that suppress the immune system.

Scientists recommend not taking andrographis if you are pregnant or planning to have a baby because it might affect fertility.

Echinacea

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 stimulate 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 the common cold, but it’s not clear whether it reduces the risk of COVID-19 or the severity of disease. In one study, healthy people who took echinacea were less likely to test positive for COVID-19, but echinacea did not affect their chances of becoming ill with symptoms from COVID-19.

Is it safe?

Side effects of echinacea can include sleeplessness, skin rashes, an upset stomach, and diarrhea.

Echinacea might reduce the effectiveness of some medications, including those that suppress the immune system.

Scientists recommend not taking echinacea if you are pregnant because they do not know if it is safe to use during pregnancy.

Elderberry

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 the symptoms of the common cold and flu and help people recover more quickly. However, it has not been studied for COVID-19, so whether it affects the risk of COVID-19 or the severity of disease is not known.

Is it safe?

Elderberry flowers and ripe fruit appear to be safe to eat. However, the bark, leaves, seeds, and raw or unripe elderberry fruit can be poisonous and can cause nausea, vomiting, diarrhea, and dehydration. Cooked elderberry fruit and properly manufactured supplements do not have this safety concern.

Elderberry might reduce the effectiveness of medications that suppress the immune system.

Scientists recommend not taking elderberry if you are pregnant because they do not know if it is safe to use during pregnancy. Elderberry might also be unsafe for people with diabetes because it might affect insulin and blood sugar levels.

Ginseng

Ginseng (Panax ginseng or Panax quinquefolius) is a plant that is 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 protect against the common cold, flu, or other upper respiratory tract infections. Ginseng has not been studied for COVID-19, so whether it affects the risk of COVID-19 or the severity of disease is not known.

Is it safe?

Side effects of ginseng can include headache, trouble sleeping, and an upset stomach. High doses (more than 2.5 grams [g]/day) of ginseng might cause insomnia, rapid heartbeat, high blood pressure, and nervousness.

Ginseng might interact with diabetes medications, stimulants, and medications that suppress the immune system.

Some scientists recommend not taking ginseng if you are pregnant because it might not be safe to use during pregnancy.

Magnesium

Magnesium is an essential mineral that is found mainly in beans, nuts, seeds, whole grains, and green leafy vegetables. Your body needs magnesium for making protein, bone, and DNA and to regulate muscle and nerve function, blood sugar levels, and blood pressure.

The Recommended Dietary Allowance (RDA) for magnesium ranges from 30 to 410 milligrams (mg) for infants and children, depending on age, and from 310 to 420 mg for adults.

Does it work?

People with low levels of magnesium might have high blood pressure, heart disease, type 2 diabetes, or other conditions that make it more difficult to recover from COVID-19. However, it’s unclear whether magnesium supplementation helps reduce the risk of COVID-19 or the severity of disease because it has not been well studied.

For example, one small study found that middle-aged patients who were hospitalized with COVID-19 were less likely to need oxygen therapy, intensive care support, or both when they received daily supplements of magnesium plus vitamins D and B12.

In another study, patients with moderate COVID-19 were given either 300 mg magnesium or a placebo each day they were in the hospital. Patients who received magnesium were less likely to need oxygen therapy, but their breathing rates were no better and their hospital stays were no shorter than patients who received a placebo.

Is it safe?

Magnesium from foods is safe in any amount. Magnesium from dietary supplements or medications that contain magnesium (such as some laxatives) is safe at daily intakes up to 65 to 350 mg for children, depending on age, and up to 350 mg for adults. Taking more can cause diarrhea, nausea, and stomach cramping. Extremely high doses can cause more serious problems, including irregular heartbeat and cardiac arrest.

Magnesium supplements can interact with some medications, including bisphosphonates (which are used to prevent bone loss), antibiotics, diuretics, and proton pump inhibitors (which are used to reduce stomach acid).

For more information, read the Office of Dietary Supplements (ODS) fact sheet on magnesium.

Melatonin

Melatonin is a hormone that helps regulate your sleep–wake cycle. It might also enhance the immune system, act as an antioxidant, and reduce inflammation.

Does it work?

A few studies have found that people with COVID-19 who received melatonin in addition to standard care for COVID-19 had milder symptoms than those who received just standard care. However, these studies were small and did not have a placebo group. For example, in one study in patients with mild to moderate COVID-19, patients who received 9 mg melatonin each day plus the standard care for COVID-19 were less likely to have extreme tiredness, cough, or difficulty breathing than the patients who received standard care without melatonin. They were also discharged from the hospital sooner.

Is it safe?

Melatonin appears to be safe for short-term use at typical doses of 1 to 10 mg/day, depending on age. High blood levels of melatonin might cause delayed puberty in children and teenagers and lower testosterone and sperm levels. It can also cause dizziness, headache, nausea, upset stomach, rash, and sleepiness.

Melatonin might increase the risk of bleeding if it is used with blood thinners, and it might also reduce the effectiveness of anticonvulsants and medications that suppress the immune system.

Some scientists recommend not taking melatonin if you are pregnant or breastfeeding because it might affect how the ovaries work.

N-acetylcysteine

N-acetylcysteine (NAC) acts as an antioxidant and helps reduce mucus in the respiratory tract (mouth, nose, throat, and lungs). NAC might also enhance the immune system, help fight viruses, and reduce inflammation.

Does it work?

NAC might help reduce the severity of the symptoms of bronchitis, chronic obstructive pulmonary disease, and similar disorders that affect breathing, but its effects on COVID-19 are unclear. One small study found that giving 600 mg NAC twice a day for 2 weeks to patients who were hospitalized with moderate or severe COVID-19 lowered the chance of needing a ventilator and of dying.

In another trial, patients who had COVID-19 or were suspected of having COVID-19 received intravenous NAC or a placebo. This form of NAC is considered a drug, not a supplement. NAC did not reduce the number of patients who were admitted to the intensive care unit (ICU) or the time patients spent in the ICU. It also did not reduce the likelihood of needing a ventilator or dying from the disease.

Is it safe?

Side effects of NAC can include nausea, vomiting, stomach pain, diarrhea, indigestion, and heartburn. NAC might disrupt blood clotting and lower blood pressure.

Taking NAC with nitroglycerine (which is used to treat chest pain) might cause low blood pressure and severe headaches.

Omega-3 fatty acids

Omega-3s are polyunsaturated fatty acids that are 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?

A few studies suggest that omega-3s might help reduce the risk of COVID-19 or the severity of disease, but other studies do not. For example, 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 and lung and kidney function in critically ill patients who were hospitalized with COVID-19. Other research found that taking cod liver oil daily did not lower the risk of COVID-19 or the severity of disease.

Are they safe?

Omega-3 supplements are safe at doses up to about 5 g/day for adults. Side effects include a bad taste in the mouth, bad breath, heartburn, nausea, digestive discomfort, diarrhea, headache, and smelly sweat.

Omega-3s might interact with blood thinners and blood pressure medications.

For more information, read the ODS fact sheet on omega-3 fatty acids.

Probiotics

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 reduce inflammation, increase immune function, and help fight viruses. However, there are many different types and combinations of probiotics, and their health effects can differ.

Do they work?

Probiotics might help protect against some respiratory tract infections. Some studies suggest that probiotics might help reduce the severity of COVID-19, but it’s unclear whether probiotics affect the risk of COVID-19. For example, one study found that people who reported taking probiotic supplements were less likely to get COVID-19. In another study, patients who were given Lactobacillus rhamnosus were slower to develop symptoms, but they were just as likely to get COVID-19.

In one study of patients who were hospitalized with COVID-19, those who received a combination of Streptococcus, Lactobacillus, and Bifidobacterium probiotics were less likely to have diarrhea, fever, weakness, headaches, muscle pain, and breathing problems and were also less likely to need intensive care, experience respiratory failure, and die than patients who received the same treatment but without probiotics. In another study, adults with COVID-19 took either one probiotic capsule or one placebo each day. After 1 month, almost twice as many of the patients who took the probiotic were symptom-free and virus-free compared with those who took the placebo.

Are they safe?

Probiotics are considered safe for most people. Side effects can include gas and other digestive symptoms. In people who are very ill or who have immune system problems, probiotics might cause severe illness. Probiotics might also cause infections or even life-threatening illness in preterm infants.

Although probiotics don’t appear to interact with medications, taking antibiotics or antifungal medications might decrease the effectiveness of some probiotics.

For more information, read the ODS fact sheet on probiotics.

Quercetin

Quercetin is a flavonoid. Flavonoids are naturally present in many fruits, vegetables, spices, and beverages. Citrus fruits, apples, onions, berries, broccoli, cilantro, dill, tea, and red wine are all rich in flavonoids. Quercetin might enhance the immune system, act as an antioxidant, reduce inflammation, and protect against viruses.

Does it work?

Quercetin has been studied to see if it reduces the risk of upper respiratory tract infections or reduces the severity of symptoms, but it’s not clear whether it helps. It’s also unclear whether quercetin helps reduce the risk of COVID-19 or the severity of disease because it has not been well studied.

Is it safe?

No serious side effects have been reported in people who have used quercetin supplements.

Quercetin might interact with some medications, including medications that suppress the immune system, pravastatin (which is used to treat high cholesterol), fexofenadine (which is used to treat allergies and hives), and blood pressure medicines.

Selenium

Selenium is an essential mineral that is found in many foods, including Brazil nuts, seafood, meat, poultry, eggs, dairy products, and grain products. It acts as an antioxidant and helps reduce inflammation. It is also important for reproduction, thyroid gland function, making DNA, and healthy immune function.

The RDA for selenium ranges from 15 to 70 micrograms (mcg) for infants and children, depending on age, and from 55 to 70 mcg for adults.

Does it work?

It’s not known whether selenium helps reduce the risk of COVID-19 or the severity of disease because it has not been well studied.

Is it safe?

Selenium is safe at daily intakes up to 45 to 400 mcg for infants and children, depending on age, and up to 400 mcg for adults. Higher intakes can cause a garlic odor in the breath, a metallic taste in the mouth, hair and nail loss or brittleness, nausea, diarrhea, skin rashes, extreme tiredness, irritability, and nervous system problems.

Selenium might interact with cisplatin (a drug used in chemotherapy).

For more information, read the ODS fact sheet on selenium.

Vitamin C

Vitamin C is an essential nutrient that is found in citrus fruits and many other fruits and vegetables. Vitamin C is important for healthy immune function.

The RDA for vitamin C 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?

Results have been mixed from studies that examined whether vitamin C helps reduce the risk of COVID-19 or the severity of disease. In a study of patients who were receiving intensive care for COVID-19, some patients were given vitamin C (plus zinc), but these supplements did not lower the risk of dying from COVID-19. However, in another study, patients with COVID-19 who were on ventilators and who received vitamin C were less likely to die than patients who did not receive vitamin C.

In another study, people with COVID-19 who were not hospitalized were given 8,000 mg vitamin C, or 50 mg zinc, or both, for 10 days, along with the standard care for COVID-19. None of the supplements reduced the number of days people had symptoms.

Vitamin C can also be given intravenously, but this form is considered a drug, not a supplement. Several studies have examined whether intravenous vitamin C might help people with COVID-19. One large study found that intravenous vitamin C was not effective and did not reduce the risk of dying from COVID-19. Other studies reported similar results; however, for some patients who were receiving intravenous vitamin C, their symptoms did not last as long, and they were discharged from the hospital sooner.

The National Institutes of Health (NIH) COVID-19 Treatment Guidelines do not recommend vitamin C for hospitalized patients with COVID-19. For people who have COVID-19 but are not hospitalized, the NIH Treatment Guidelines state that there’s not enough evidence one way or the other to recommend vitamin C.

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 stomach cramps and might also cause false readings on blood sugar monitors. In people with hemochromatosis (an iron overload disorder), high amounts of vitamin C might cause iron build-up in the body, which can damage body tissues.

Vitamin C supplements might decrease the effectiveness of radiation therapy and chemotherapy.

For more information, read the ODS fact sheet on vitamin C.

Vitamin D

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 when your skin is exposed to the sun. Vitamin D is important for healthy bones and immune function.

The RDA for vitamin D ranges from 10 to 15 mcg (400 to 600 International Units [IU]) for infants and children, depending on age, and from 15 to 20 mcg (600 to 800 IU) for adults.

Does it work?

Vitamin D might help protect against some respiratory tract infections, especially in people with low vitamin D levels. Some studies show that low vitamin D levels are linked to a higher risk of COVID-19, more severe disease, and a higher risk of death, but other studies do not. Some research suggests that people who regularly take vitamin D supplements might be less likely to develop COVID-19. However, the NIH COVID-19 Treatment Guidelines state that there’s not enough evidence one way or the other to recommend using vitamin D to prevent or treat COVID-19.

In one study, health care workers who were caring for patients with COVID-19 were given 100 mcg (4,000 IU) vitamin D or a placebo each day. This study took place before COVID-19 vaccines were available. Health care workers who received vitamin D were less likely to get COVID-19 than those who received a placebo.

In a study in people who were hospitalized with moderate to severe COVID-19, those who were given a single dose of 5,000 mcg (200,000 IU) vitamin D did not have a shorter hospital stay or a lower risk of death, and they were not less likely to need a ventilator. This was true even for patients whose vitamin D levels were low when they entered the hospital.

In another study, older adults who were hospitalized with COVID-19 were given either 10,000 mcg (400,000 IU) or 1,250 mcg (50,000 IU) vitamin D. After 2 weeks, fewer patients in the group that received the higher dose had died. However, the number of patients who were still alive after 4 weeks was similar between the groups. Another study gave patients who were hospitalized with COVID-19 either 12,500 mcg (500,000 IU) vitamin D or a placebo. The patients who received the single dose of vitamin D weren’t able to breathe easier, weren’t discharged from the hospital any sooner, weren’t less likely to be admitted to the ICU, and weren’t less likely to die in the hospital than the patients who received a placebo.

One study is underway to see whether vitamin D helps reduce the severity of COVID-19 and helps reduce the risk of spreading COVID-19 to people they live with.

Is it safe?

Vitamin D is safe at daily intakes up to 25 to 100 mcg (1,000 to 4,000 IU) for infants and 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.

Vitamin D supplements might interact with some medications, such as orlistat (which is used for weight loss), statins (which are used to lower cholesterol levels), thiazide diuretics (which are used to treat high blood pressure), and steroids.

For more information, read the ODS fact sheet on vitamin D.

Vitamin E

Vitamin E (also called alpha-tocopherol) is an essential nutrient that is found in nuts, seeds, vegetable oils, and green leafy vegetables. It acts as an antioxidant and helps your immune system function properly.

The RDA for vitamin E is 4 to 15 mg for infants and children, depending on age, and 15 to 19 mg for adults.

Does it work?

Some studies suggest that vitamin E supplements help reduce the risk of upper respiratory tract infections, but other studies do not.

It’s not known whether vitamin E reduces the risk of COVID-19 or the severity of disease because it has not been well studied.

Is it safe?

Vitamin E in food is safe at any level. In supplements, vitamin E is safe at daily intakes up to 200 to 800 mg for infants and children, depending on age, and up to 1,000 mg/day for adults. Higher intakes can increase the risk of bleeding and stroke.

Vitamin E supplements might interact with blood thinners and might reduce the effectiveness of radiation therapy and chemotherapy.

For more information, read the ODS fact sheet on vitamin E.

Zinc

Zinc is an essential nutrient that is present in the highest amounts in oysters, crab, lobster, beef, pork, and poultry. Beans, nuts, whole grains, and dairy products also contain zinc. Zinc is important for a healthy immune system, making proteins and DNA, healing wounds, and for the sense of taste.

The RDA for zinc ranges from 2 to 13 mg for infants and children, depending on age, and from 8 to 12 mg for adults.

Does it work?

Zinc lozenges might help reduce the number of days the common cold lasts. It’s unclear whether zinc helps reduce the risk of COVID-19 or the severity of disease. Some studies link low zinc levels to a higher risk of COVID-19 and more severe disease, but other studies do not.

In one study, people who had COVID-19 who were not hospitalized were given 50 mg zinc, or 8,000 mg vitamin C, or both, for 10 days, along with the standard care for COVID-19. None of the supplements reduced the number of days people had symptoms. In another study of patients with COVID-19, some of whom were hospitalized, patents were given either 25 mg zinc two times a day or a placebo. The patients who received zinc were less likely to be admitted to the ICU and were discharged from the hospital sooner than people who took the placebo. Among the outpatients who took zinc, symptoms lasted fewer days than in the people who took the placebo.

The NIH COVID-19 Treatment Guidelines recommend against using doses of zinc supplements that are above the RDA to prevent COVID-19, except for research purposes. They also state that there’s not enough evidence one way or the other to recommend zinc to treat COVID-19.

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, stomach cramps, diarrhea, and headaches. High intakes of zinc over a long period of time can reduce immune system function and levels of copper in the blood.

Zinc supplements might interact with antibiotics, penicillamine (which is used to treat rheumatoid arthritis), and thiazide diuretics (which are used to treat high blood pressure).

For more information, read the ODS fact sheet on zinc.

Do dietary supplements interact with medications or other supplements?

Yes, some supplements can interact or interfere with medicines you take.

Tell your doctor, pharmacist, and other health care providers about any dietary supplements and prescription or over-the-counter medicines you take. They can tell you if the dietary supplements might interact with your medicines or if the medicines might interfere with how your body absorbs, uses, or breaks down nutrients.

Disclaimer

This fact sheet by the National Institutes of Health (NIH) Office of Dietary Supplements (ODS) provides information that should not take the place of medical advice. We encourage you to talk to your health care 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.

Glossary

absorption: In nutrition, the process of moving protein, carbohydrates, fats, and other nutrients from the digestive system into the bloodstream. Most absorption occurs in the small intestine.
acute: Sudden, severe, and not long lasting.
adverse event: An unwanted medical problem that occurs during treatment. Adverse events may be unrelated to the treatment or they may be caused by the therapy or procedure. For example, an adverse event may be caused by the toxic effects of a particular drug or dietary supplement or by an interaction with another therapy. Also called adverse effect and side effect.
alpha-tocopherol: The form of vitamin E that is found in the largest amount in humans and is the most active form of vitamin E. It is an antioxidant.
antibiotic: A drug used to treat infections caused by bacteria and other microorganisms.
anticonvulsant: A drug that prevents, reduces, or stops convulsions or seizures.
antioxidant: A substance that protects cells from damage caused by free radicals (compounds formed during the metabolism of oxygen). It may help prevent the development of some chronic diseases such as cancer. Antioxidants include beta-carotene; lutein; lycopene; vitamins A, C, and E; selenium; and zinc.
bacteria: Single-celled organisms that are too small to be seen without a microscope. Bacteria are found everywhere and may be helpful or harmful.
blood sugar: The main source of energy used by the body's cells. Blood sugar comes from food and is made by the liver, and is carried to the cells through the bloodstream. Also called blood glucose.
blood vessel: A tube through which blood circulates in the body. Blood vessels include a network of arteries, arterioles, capillaries, venules, and veins.
capsule: A gelatin shell containing a dose of medicine, a vitamin, or other dietary supplement.
cardiac arrest: A condition in which the heart suddenly stops beating.
cell: The individual unit that makes up the tissues of the body. All living things are made up of one or more cells, which are the smallest units of living structure capable of independent existence.
cell membrane: An envelope that contains the contents of a cell and controls what passes into and out of the cell.
chemotherapy: A chemical that kills bacteria, viruses, fungi, or tumor cells. It usually refers to drugs used in cancer treatment.
cholesterol: A substance found throughout the body. It is made by the liver and is an important component of cells. Cholesterol is also used to make hormones, bile acid, and vitamin D. Foods that come from animals contain cholesterol, including eggs, dairy products, meat, poultry and fish. High blood levels of cholesterol increase a person's chance (risk) of developing atherosclerosis and heart disease.
chronic: Happening for a long time, persistently, or repeatedly.
common cold: A nose and throat infection caused by a virus. Symptoms include runny nose, sneezing, congestion, sore throat, and cough.
copper: In nutrition, a mineral the body needs (along with iron) to make red blood cells. Copper also helps keep the immune system, blood vessels, nerves, and bones healthy. Copper is found in some foods, including oysters and other shellfish, whole grains, beans, nuts, potatoes, organ meats, dark leafy greens, and dried fruits.
dairy food: Milk and products made with milk, such as buttermilk, yogurt, cheese, cottage cheese, and ice cream.
deoxyribonucleic acid: DNA. The molecules inside cells that carry genetic information and pass it from one generation to the next.
diabetes: A disease in which blood sugar (glucose) levels are high because the body is unable to use glucose properly. Diabetes occurs when the body does not make enough insulin, which helps the cells use glucose, or when the body no longer responds to insulin.
diarrhea: Loose, watery stools.
dietary supplement: A product that is intended to supplement the diet. A dietary supplement contains one or more dietary ingredients (including vitamins, minerals, herbs or other botanicals, amino acids, and other substances) or their components; is intended to be taken by mouth as a pill, capsule, tablet, or liquid; and is identified on the front label of the product as being a dietary supplement.
disorder: In medicine, a disturbance of normal functioning of the mind or body. Disorders may be caused by genetic factors, disease, or trauma.
diuretic: A drug or other substance that increases the amount of urine made by the body.
dose: The amount of medicine or other substance taken at one time or over a specific period of time.
drug: Any substance (other than food) that is used to prevent, diagnose, treat, or relieve symptoms of a disease or abnormal condition. Also, a substance that alters mood or body function or that can be habit-forming or addictive, especially a narcotic.
echinacea: A plant that is native to North America. Traditionally, it has been used for colds, flu, and other infections.
effectiveness: In medicine, the ability of an intervention (for example, a drug, surgery, or a dietary supplement) to produce the desired beneficial effect under the usual conditions of care by a health care provider.
endocrine system: Hormone-producing glands that affect growth and development, hunger, metabolism (chemical changes in the body), sleep, sexual function, and mood. The endocrine system includes the thyroid gland, pituitary gland, adrenal gland, parathyroid glands, adrenal glands, pancreas, ovaries, and testicles.
essential: In nutrition, essential nutrients are ones that we must consume for good health because our bodies cannot make them. Essential nutrients include vitamins and minerals.
evidence: Information used to support the use of a particular screening procedure, treatment, or preventive measure. In medicine, evidence needed to determine effectiveness is provided by laboratory research, clinical trials, and other studies.
flavonoids: Substances that naturally occur in many plants. Green tea, cocoa, coffee, red wine, berries, apples, citrus fruit, and cruciferous and colorful vegetables contain significant amounts of flavonoids. Plant foods contain more than 6,000 flavonoids, including flavanols, flavones, flavonols, flavanones, anthocyanidins, flavan-3-ols, and isoflavones.
fortified: When nutrients (such as vitamins and minerals) are added to a food product. For example, when calcium is added to orange juice, the orange juice is said to be "fortified with calcium". Similarly, many breakfast cereals are "fortified" with several vitamins and minerals.
gland: A small organ that makes and releases a substance such as sweat, tears, saliva, milk, a hormone, or substances that aid in digestion.
gram: g. A measure of weight. It is a metric unit of mass equal to 0.001 kilogram (it weighs 0.035 ounce).
health care provider: A person who supplies health care services. Health care providers include individuals with professional training (including doctors, nurses, technicians, and aides).
heart rhythm: The regular beating of the heart as it moves blood throughout the body.
hemochromatosis: A condition in which the body absorbs more iron than it needs and stores it in the liver, heart, and pancreas. Hemochromatosis causes liver disease, heart problems, and organ failure.
herb: A plant used in cooking, in tea, and for medicinal purposes.
herbal: Having to do with or made from medicinal or edible plants.
high blood pressure: A blood pressure measurement of 140/90 mmHg (millimeters of mercury) or higher is considered high blood pressure (hypertension). Blood pressure is the force of blood pushing against the walls of the arteries. Blood pressure measurements are written as two numbers, for example 120/80. The first number (the systolic pressure) measures the pressure when the heart beats and pumps out blood into the arteries. The second number (the diastolic pressure) measures the pressure when the heart is at rest between beats. High blood pressure is a condition that occurs when a person's blood pressure often measures above 140/90 or regularly stays at that level or higher. This condition usually has no symptoms but can be life-threatening. It damages the arteries and increases the chance of stroke, heart attack, kidney failure, and blindness. Also called hypertension.
hives: Raised red bumps or patches on the surface of the skin that come and go and itch, burn, or sting. They are usually caused by an allergic reaction to drugs, food, or insect bites. Also called urticaria.
hormone: A group of chemicals made by glands in the body. Hormones circulate in the bloodstream and control the actions of certain cells or organs. Some hormones can also be manufactured.
immune function: Substances made and action taken by cells that fight disease and infection.
immune system: A group of organs and cells that defends the body against infection, disease, and altered (mutated) cells. It includes the thymus, spleen, lymphatic system (lymph nodes and lymph vessels), bone marrow, tonsils, and white blood cells.
immunity: The condition of being protected against or resistant to an infectious disease.
infant: A child younger than 12 months old.
infection: The invasion and spread of germs in the body. The germs may be bacteria, viruses, yeast, or fungi.
inflammation: Redness, swelling, pain, and/or a feeling of heat in an area of the body. It is a protective reaction to injury, disease, or irritation of tissues.
ingredient: In a dietary supplement, an ingredient is a component of the product, such as the main nutrient (vitamin, mineral, herb, amino acid, or enzyme) or any binder, color, filler flavor, or sweetener. In herbal supplements, the common name and Latin name (the genus and species) of the plant is given in the ingredient list. On a dietary supplement label, the ingredients are listed by weight, with the ingredient used in the largest amount first on the list and the ingredient used in the least amount at the end of the list.
insomnia: Difficulty in going to sleep or in getting enough sleep.
interaction: A change in the way a dietary supplement acts in the body when taken with certain other supplements, medicines, or foods, or when taken with certain medical conditions. Interactions may cause the dietary supplement to be more or less effective, or cause effects on the body that are not expected.
International Unit: IU. A measurement used to measure the activity of some vitamins and other biological substances (such as enzymes and hormones).
intravenous: Into or within a vein, such as an intravenous injection.
iron: In nutrition, a mineral the body needs to make red blood cells, proteins, and enzymes; and for the control of cell growth and cell specialization. Iron is found in some foods, including red meats, fish, poultry, lentils, and beans.
IU: International Unit. A measurement used to measure the activity of some vitamins and other biological substances (such as enzymes and hormones).
kidney: One of two organs that remove waste from the blood (as urine). The kidneys also make erythropoietin (a substance that stimulates red blood cell production) and help regulate blood pressure. The kidneys are located near the back under the lower ribs.
kidney failure: Loss of kidney function. When kidney failure is caused by an acute (sudden and short-term) condition, such as a traumatic injury or poisoning, the kidneys may be able to recover. Usually, however, kidney failure is caused by chronic (long-term) conditions such as high blood pressure and diabetes. Chronic diseases permanently damage kidney tissue; treatments include dialysis and kidney transplantation.
kidney stone: A “pebble” that forms in a kidney from salts and minerals in the urine. A small kidney stone is able to pass out of the body; a large stone may block the urinary tract and require medical help.
laxative: A substance that moves the bowels and relieves constipation.
liver: A large organ located in the right upper abdomen. It stores nutrients that come from food, makes chemicals needed by the body, and breaks down some medicines and harmful substances so they can be removed from the body.
lozenge: A small, hard candy containing medicine that is dissolved in the mouth.
lung: An organ in the chest that supplies oxygen to the body and removes carbon dioxide. There are two lungs in the body.
magnesium: In nutrition, a mineral the body needs for normal muscles, nerves, and bones. It also helps keep a steady heart rhythm, a healthy immune system, normal blood sugar levels and blood pressure, and is involved in making energy and protein for the body. Magnesium is found in some foods, including green vegetables, beans and peas, nuts and seeds, and whole grains.
microgram: µg or mcg. A unit of weight in the metric system equal to one millionth of a gram. (A gram is approximately one-thirtieth of an ounce.)
microorganism: A living being that can be seen only through a microscope. Microorganisms include helpful and harmful bacteria, protozoa, algae, and fungi. Although viruses are not considered living organisms, they are sometimes classified as microorganisms.
milligram: mg. A measure of weight. It is a metric unit of mass equal to 0.001 gram (it weighs 28,000 times less than an ounce).
mineral: In nutrition, an inorganic substance found in the earth that is required to maintain health.
National Institutes of Health: NIH. The main organization in the federal government responsible for conducting and supporting medical research. It is composed of 27 Institutes and Centers that provide financial support to researchers in the United States and throughout the world to investigate ways to prevent, treat, and cure common and rare diseases. NIH is part of the US Department of Health and Human Services.
nausea: The uneasy feeling of having an urge to throw up (vomit).
nervous system: The brain and spinal cord, including the network of nerves that carry messages back and forth between the brain and all parts of the body. The nervous system controls what the body does.
neuron: A nerve cell. Neurons send chemical and electrical messages throughout the nervous system that direct the body to function, move, think, and have emotions.
nutrient: A chemical compound in food that is used by the body to function and maintain health. Examples of nutrients include proteins, fats, carbohydrates, vitamins, and minerals.
Office of Dietary Supplements: ODS, Office of Disease Prevention, Office of Director, National Institutes of Health, Department of Health and Human Services. ODS strengthens knowledge and understanding of dietary supplements by evaluating scientific information, stimulating and supporting research, disseminating research results, and educating the public to foster an enhanced quality of life and health for the US population.
ovary: One of a pair of female reproductive glands in which the eggs (ova) are formed and stored. The ovaries are located in the pelvis, one on each side of the uterus.
pharmacist: A person licensed to make and dispense (give out) prescription drugs and who has been taught how they work, how to use them, and their side effects.
placebo: An inactive substance or treatment that has no effect on the body and that ideally looks, smells, and tastes the same as, and is given the same way as, the active drug or treatment being tested. The effects of the active substance or treatment are compared to the effects of the placebo.
pneumonia: Inflammation of one or both lungs. Bacteria, viruses, fungi, parasites, other germs, and injury can cause the lungs to become inflamed and fill with fluid. Symptoms can appear suddenly, range from mild to severe, and may include fever, chills, chest pain, cough, shortness of breath, and difficult breathing. Anyone can develop pneumonia, but it is especially dangerous in babies, older people, and people with weakened immune systems, lung disease, heart disease, or diabetes.
poultry: Birds that are raised for eggs or meat, including chickens, turkeys, ducks, and geese.
prescription: A written order from a health care provider for medicine, therapy, or tests.
prevent: To stop from happening.
protein: A molecule made up of amino acids that the body needs for good health. Proteins are the basis of body structures such as skin and muscle, and substances such as enzymes and antibodies.
proton pump inhibitor: PPI. A drug that reduces the amount of acid made by the stomach. It is used to treat peptic ulcer and gastroesophageal reflux disease.
radiation therapy: The use of high-energy radiation from x-rays and other sources to kill cancer cells, shrink tumors, and treat other conditions.
Recommended Dietary Allowance: RDA. The average amount of a nutrient a healthy person should get each day. RDAs vary by age, gender and whether a woman is pregnant or breastfeeding. For example, the RDA for vitamin C is 80 mg a day for a pregnant teenager and 90 mg a day for men. RDAs are developed by the Food and Nutrition Board at the Institute of Medicine of the National Academies.
regulate: To govern, make uniform, and bring under the control of a rule, principle, or legal system. In the United States, the FDA has the authority to regulate dietary supplements.
respiratory: Having to do with breathing. The organs that are involved with breathing include the mouth, nose, throat (pharynx), voicebox (larynx), windpipe (trachea), air passages between the windpipe and lungs (bronchial tubes), and lungs.
respiratory tract: The organs that are involved in breathing. These include the mouth, nose, throat (pharynx), voicebox (larynx), windpipe (trachea), air passages between the windpipe and lungs (bronchial tubes), and lungs. Also called the respiratory system.
rheumatoid arthritis: An autoimmune disease that causes pain, swelling, and stiffness in the joints. It may cause severe joint damage, loss of function, and disability. The disease may last from months to a lifetime, and symptoms may improve and worsen over time.
risk: The chance or probability that a harmful event will occur. In health, for example, the chance that someone will develop a disease or condition.
scientific literature: Published peer-reviewed original research in the sciences and social sciences.
selenium: A mineral required in very small amounts to make important enzymes that are essential for good health. Selenium is found in some foods, including plant foods grown in selenium-rich soil, and some meats and seafood.
sign: An indication of disease that can be seen and/or measured. Examples include high fever, high blood pressure, infection, and coughing up blood.
soy: A plant that produces beans used in many food products. Soy products contain isoflavones (estrogen-like substances) that are being studied in the prevention of cancer, hot flashes that occur with menopause, and osteoporosis (loss of bone density). Also called soya and soybean. Latin name: Glycine max.
statin: A drug used to treat high cholesterol. Statins lower the amount of cholesterol and certain fats in the blood.
stimulant: A substance that increases brain activity, alertness, attention, blood pressure, heart rate, breathing, and energy.
stroke: A loss of blood flow to part of the brain. Strokes are caused by blood clots or broken blood vessels in the brain, and result in damage to a section of brain tissue. Symptoms include dizziness, numbness, weakness on one side of the body, and problems with talking or understanding language. The chance (risk) of stroke is increased by high blood pressure, older age, smoking, diabetes, high cholesterol, heart disease, a family history of stroke, and a build-up of fatty material inside the coronary arteries (atherosclerosis). See also NIH publication: Know Stroke. Know the Signs. Act in Time. http://www.ninds.nih.gov/disorders/stroke/knowstroke.htm
supplement: A nutrient that may be added to the diet to increase the intake of that nutrient. Sometimes used to mean dietary supplement.
symptom: A feeling of sickness that an individual can sense, but that cannot be measured by a healthcare professional. Examples include headache, tiredness, stomach ache, depression, and pain.
tea: A drink made by adding boiling water to fresh or dried herbs and steeping (soaking) them. It may be drunk either hot or cold. Also called an infusion.
thiazide diuretic: A drug used in the treatment of high blood pressure and swelling caused by excess fluid in body tissues (edema). It increases the amount of urine made by the body.
thyroid: A gland located in the front of the neck, below the larynx (Adam’s apple). The thyroid makes hormones that circulate in the bloodstream and affect brain development, metabolism, weight, breathing, heart rate, blood pressure, nervous system functions, body temperature, muscle strength, skin dryness, menstrual cycles, and cholesterol levels.
tissue: A group or layer of cells in a living organism that work together to perform a specific function.
treat: To care for a patient with a disease by using medicine, surgery, or other approaches.
Ventilator: In medicine, a machine used to help a patient breathe. Also called respirator.
virus: An organism that can grow and multiply only inside the cells of living humans, plants, or animals. It is able to change (mutate) as it multiplies, which makes viral illnesses difficult to treat. Viruses cause many infections and diseases such as the common cold, AIDS (acquired immunodeficiency syndrome), herpes, and hepatitis.
vitamin: A nutrient that the body needs in small amounts to function and maintain health. Examples are vitamins A, C, and E.
vitamin C: A nutrient needed by the body to make collagen (a protein found in cartilage, tendons, ligaments, bone, and blood vessels), to absorb iron from food, and for wound healing. It is an antioxidant and protects cells from free radical damage. Vitamin C is found in some foods including citrus fruits, strawberries, peppers, dark green vegetables, tomatoes, and potatoes. Also called ascorbic acid.
vitamin D: A nutrient that is obtained from the diet and can be made in the skin after exposure to sunlight. Vitamin D acts as a hormone. It helps to form and maintain strong bones, maintain normal blood levels of calcium and phosphorus, and increase calcium absorption; it also helps to maintain a healthy immune system and control cell growth. Vitamin D is found in some foods, including some types of fatty fish, and milk and breakfast cereals that are fortified with vitamin D.
vitamin E: A nutrient needed by the body to help keep the immune system healthy and to repair damage to DNA. It is an antioxidant that protects cells from free radical damage. Vitamin E is found in some foods, including vegetable oils, nuts and seeds, fortified breakfast cereals, and spinach, broccoli, kiwi, and mangos.
white blood cell: WBC. A cell made by the bone marrow that helps the body fight infection and disease. WBCs include lymphocytes, neutrophils, eosinophils, macrophages, and mast cells.
whole grain: Unprocessed seeds of edible grasses, including brown rice, buckwheat, bulgur, millet, popcorn, oats, quinoa, whole-grain barley, whole rye, whole wheat, and wild rice. Grains that are ground, cracked, or flaked can be labeled whole grain if they have the same amount of bran, germ, and endosperm (the inner part of the seed kernel) as the intact grain. Whole grains are sources of iron, magnesium, selenium, B vitamins, and dietary fiber. Eating whole grains may help lower the risk of heart disease, obesity, and type 2 diabetes.
zinc: A mineral found in most cells of the body. It helps enzymes work properly, helps maintain a healthy immune system, helps maintain the senses of taste and smell, and is needed for wound healing, making DNA, and normal growth and development during pregnancy, childhood, and adolescence. Zinc is found in some foods, including oysters, red meat, poultry, beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products.

Updated: May 20, 2025 History of changes to this fact sheet