Vitamin & Supplement Glossary

Last updated: November 10, 2026

A · B · C · D · E · F · G · H · I · K · L · M · N · O · P · R · S · T · U · V · W

A

Adaptogen

A traditional term for herbs and mushrooms, such as ashwagandha, rhodiola and ginseng, that have been used to help the body handle everyday stress. It is a marketing and traditional-use label rather than a scientific category, and research varies widely by plant. Browse Herbs & Botanicals.

Adequate Intake (AI)

A daily intake level used when there is not enough evidence to set an RDA. It is the amount assumed to be adequate for a group, based on what healthy people typically consume. Examples include the AI for ALA omega-3 and for infants' vitamin D. See also RDA.

ALA (alpha-linolenic acid)

The plant omega-3 fatty acid found in flaxseed, chia seeds, walnuts, and canola and soybean oils. It is an essential fat, so it must come from food. The body converts only small amounts of ALA into EPA and DHA. Flaxseed oil supplements provide ALA, not EPA or DHA.

Algae oil

An oil made from cultivated microalgae that supplies DHA, and in some products EPA. Fish get their omega-3s by eating algae, so algae oil is the plant-based way to get these fats. If a vegan or vegetarian source matters to you, look for that statement on the label. Browse Omega-3 & Fish Oil.

Ashwagandha

A root used in Ayurvedic tradition and sold as powders, capsules and standardized extracts. It is often grouped with adaptogens. Rare cases of liver injury have been reported, and it may not be suitable during pregnancy or with thyroid conditions. Talk to your doctor or pharmacist before using it, especially if you take medication.

B

BCAA (branched-chain amino acids)

Three essential amino acids, leucine, isoleucine and valine, sold as powders and capsules for training days. They are also naturally present in protein foods and in complete protein powders such as whey, so check how much you already get. Browse Protein & Sports Nutrition.

B-complex

A supplement that combines several or all eight B vitamins: thiamin, riboflavin, niacin, pantothenic acid, B6, biotin, folate and B12. B vitamins play a role in energy metabolism.† Amounts vary widely between products, so compare each one against the Daily Value and the Upper Intake Level. Browse Vitamins.

Best by date

A date, sometimes written as an expiration date, showing how long the manufacturer expects the product to meet its label claims when stored as directed. The FDA does not require supplements to carry one, but a company that uses one should have data to support it. Use products before the date.

Beta-carotene and retinyl palmitate

Two sources of vitamin A on supplement labels. Beta-carotene is a plant pigment the body converts to vitamin A as needed. Retinyl palmitate is preformed vitamin A, which counts toward the adult Upper Intake Level of 3,000 mcg RAE a day; beta-carotene does not. See RAE.

Bioavailability

The share of a nutrient that is absorbed and available for the body to use. It depends on the form of the nutrient, the rest of the meal, the dose and the person. Higher bioavailability on paper doesn't automatically make one product better than another; the right form is one you can take consistently.

Biotin

A B vitamin, also called vitamin B7, that plays a role in energy metabolism.† The Daily Value is 30 mcg, but many hair, skin and nails products contain far more. The FDA has warned that high biotin intake can interfere with some lab tests, so tell your doctor before blood work. Browse Collagen & Beauty Nutrition.

C

Capsule

A shell, usually made of gelatin or a plant material such as hypromellose, that holds a powder or oil. Capsules are often easier to swallow than large tablets and can be opened in some cases, but check the label first. The capsule material is listed under other ingredients. See vegetarian capsule.

CFU (colony forming unit)

An estimate of the number of live, viable microorganisms in a serving of a probiotic. According to the NIH Office of Dietary Supplements, many products provide 1 to 10 billion CFU per dose, and a higher number isn't necessarily better. Look for a count stated through the expiration date. Browse Probiotics & Digestive Health.

cGMP (current good manufacturing practice)

The FDA rules, found in 21 CFR Part 111, that supplement makers must follow. They require written procedures and checks for the identity, purity, strength and composition of each product. cGMP covers how a product is made; it doesn't mean the FDA approved the product. See How we choose products.

Chelated minerals

Minerals bound to amino acids or other carrier molecules, such as magnesium glycinate, zinc bisglycinate or iron bisglycinate. Chelated forms are often chosen for how they sit with the stomach. The amount on the label is still the elemental mineral, so compare products by that number. Browse Minerals.

Chlorella

A single-celled green alga sold as powders and tablets. It has a tough cell wall, so products are often labeled "broken cell wall." Because algae can absorb contaminants from where they grow, look for brands that describe their contaminant testing. Chlorella can contain vitamin K. Browse Greens & Superfoods.

Coenzyme Q10 (CoQ10)

A compound the body makes and uses in energy production inside cells. Supplements come as ubiquinone or ubiquinol, usually in softgels with oil. CoQ10 may affect how warfarin works, and statin medicines can lower the body's own levels. Talk to your doctor or pharmacist before taking it with any medication.

Collagen peptides (hydrolyzed collagen)

Collagen broken down into small protein fragments that dissolve easily in hot or cold drinks. They come from bovine, marine or chicken sources and provide protein, though collagen lacks the essential amino acid tryptophan, so it is not a complete protein. Browse Collagen & Beauty Nutrition.

Collagen types I, II and III

Labels that describe which kinds of collagen a product contains. Type I is the most common in skin, tendons and bone, type II is found mainly in cartilage, and type III often appears alongside type I. Peptide powders are usually types I and III; type II products are often sold separately.

Creatine monohydrate

The most common form of creatine, a compound made in the body and found in meat and fish. It is sold as an unflavored powder or capsules, usually in gram amounts. People with kidney disease should talk to their doctor before using it. Browse Protein & Sports Nutrition.

Cyanocobalamin

The most common form of vitamin B12 in supplements and fortified foods. It is stable and well studied, and the body converts it into the active forms it uses. People who eat no animal foods generally need B12 from fortified foods or supplements. See also methylcobalamin.

D

Daily Value (DV)

A reference amount of a nutrient set by the FDA for food and supplement labels. Daily Values let you compare products on a common scale, but they are not personal recommendations; your needs depend on age, sex, pregnancy and health. See % Daily Value and How to read a supplement label.

Daily Value not established (†)

A symbol, often a dagger (†), placed in the % Daily Value column for ingredients that have no Daily Value, such as most herbs, omega-3s and probiotics. It doesn't mean the amount is high or low. The same symbol may also link a claim to the FDA disclaimer, so read the footnote.

Delayed release

A capsule or tablet designed to pass through the stomach before it opens, usually in the small intestine. It is often used for fish oil, to reduce aftertaste, and for some probiotics. Don't crush or open delayed-release products unless the label says you can. See also enteric coated.

DFE (dietary folate equivalents)

The unit used for folate on Supplement Facts labels. It accounts for the fact that folic acid from supplements is absorbed better than folate from food. The label may also show the amount of folic acid in parentheses. See folic acid and methylfolate.

DHA (docosahexaenoic acid)

A long-chain omega-3 fatty acid found mainly in fatty fish and algae. DHA is a building block of cell membranes in the brain and eyes.† Labels list DHA in milligrams per serving, and many prenatal formulas add it. Add EPA and DHA together when comparing products. Browse Omega-3 & Fish Oil.

Dietary supplement

A product taken by mouth that contains a dietary ingredient, such as a vitamin, mineral, herb, amino acid or probiotic, and is labeled as a supplement. In the U.S., supplements are regulated as a category of food, and the FDA doesn't approve them before they're sold. See Supplement safety.

Digestive enzymes

Supplements containing enzymes such as amylase, protease and lipase, which help break down carbohydrates, proteins and fats, or lactase, which breaks down the milk sugar lactose. Activity is often listed in special units rather than milligrams. Browse Probiotics & Digestive Health.

E

Echinacea

A group of flowering plants in the daisy family, sold as teas, tinctures and capsules. Products vary by species and plant part. People allergic to ragweed, chrysanthemums, marigolds or daisies may react to echinacea. Talk to your doctor or pharmacist if you take medication that affects the immune system. Browse Immune Support.

Elderberry

The dark berry of the elder plant, sold as syrups, gummies and lozenges. Supplements use cooked or processed berries, because raw or unripe berries, leaves and stems can cause nausea and vomiting. Check the extract strength and sugar per serving. Browse Immune Support.

Electrolytes

Minerals that carry an electric charge in body fluids, mainly sodium, potassium, chloride and magnesium. Electrolyte mixes are often used for long or hot workouts. Check the sodium and sugar per serving, and ask your doctor if you limit sodium or take medication. Browse Protein & Sports Nutrition.

Elemental magnesium

The amount of magnesium itself in a supplement, not the weight of the whole compound. A label reading "Magnesium (as magnesium glycinate) 120 mg" provides 120 mg of magnesium. The same idea applies to calcium, zinc and iron. Use elemental amounts when comparing products and counting toward the 350 mg daily limit for supplemental magnesium.

Enteric coated

A coating that resists stomach acid so the tablet or capsule dissolves later, in the small intestine. It is used to protect sensitive ingredients or reduce stomach upset and aftertaste. Swallow enteric-coated products whole. See also delayed release.

EPA (eicosapentaenoic acid)

A long-chain omega-3 fatty acid found mainly in fatty fish and some algae oils. Labels list EPA in milligrams per serving. A typical 1,000 mg fish oil softgel provides about 180 mg EPA and 120 mg DHA, so read the panel, not the front of the bottle. Browse Omega-3 & Fish Oil.

Extract (standardized extract)

A concentrated form of an herb made by drawing compounds out of the plant with water, alcohol or other solvents. A standardized extract is adjusted to contain a set percentage of a marker compound, such as curcuminoids in turmeric. It keeps batches consistent; it doesn't by itself show that a product works.

F

Fat-soluble vitamins

Vitamins A, D, E and K, which dissolve in fat and are absorbed along with dietary fat. They are stored in the body's fat and liver, so they can build up over time. Take them with a meal that contains some fat and stay within the Upper Intake Level. See water-soluble vitamins.

FDA disclaimer

The statement required on any supplement label that makes a structure/function claim: "These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease." It means the FDA has not reviewed the claim.

Fiber and psyllium

Fiber is the part of plant foods the body doesn't digest. Psyllium husk is a soluble fiber sold as powders and capsules. Start with a small amount, drink plenty of water, and ask your pharmacist about timing, since fiber can change how some medications are absorbed. Browse Probiotics & Digestive Health.

Fish oil

Oil from fatty fish such as anchovies, sardines and mackerel, the most common source of EPA and DHA in supplements. Compare products by EPA plus DHA per serving rather than total oil. Ask your doctor first if you take a blood thinner or have a fish allergy. Browse Omega-3 & Fish Oil.

Folic acid

The synthetic form of folate used in most supplements and fortified foods such as bread and cereal. It is listed in mcg DFE, often with the folic acid amount in parentheses. The adult Upper Intake Level for folic acid from supplements and fortified foods is 1,000 mcg a day. See methylfolate.

G

Greens powder

A blend of dried vegetables, grasses, algae and other plants that you mix into water or smoothies. It can add variety, but it doesn't replace whole vegetables and fruit. Look for amounts of each ingredient rather than a proprietary blend, and check for added vitamins. Browse Greens & Superfoods.

Gummy

A chewable supplement made with gelatin or pectin, sweeteners and flavors. Gummies are easy to take but often contain added sugar, may hold smaller amounts of nutrients, and can soften in heat. Because they look like candy, store them out of children's reach. See Supplement safety.

H

Hyaluronic acid

A substance found naturally in skin, joints and the fluid around the eyes. It is sold in capsules and in hair, skin and nails formulas, usually in milligram amounts, and is also common in topical skin care. Browse Collagen & Beauty Nutrition.

I

Informed Choice and Informed Sport

Programs run by LGC that screen product samples or batches for substances banned in sport. They are used mainly by athletes and sports nutrition buyers. A logo applies only to the specific product that carries it; check the program's online directory. Read our guide to third-party seals.

IU (International Unit)

An older unit based on biological activity rather than weight. Labels now list vitamins A, D and E by weight, but many still show IU in parentheses. For vitamin D, 1 mcg equals 40 IU, so 25 mcg is 1,000 IU. See our vitamin D in winter guide.

K

Krill oil

Oil from small crustaceans called krill, with omega-3s partly in phospholipid form. Capsules often contain less EPA and DHA than fish oil, so compare the amounts per serving. Krill is a shellfish, so people with shellfish allergies should ask their doctor first. Browse Omega-3 & Fish Oil.

L

Lot number

A code on the label that identifies the production batch a product came from. It helps the manufacturer trace quality questions and recalls. If a product arrives damaged or expired, include the lot number and the date when you contact the store. See Returns & refunds.

L-theanine

An amino acid found naturally in tea leaves, sold on its own or in calming blends for relaxation. It is often combined with magnesium or chamomile in evening products. As with any supplement, talk to your doctor or pharmacist if you take medication. Browse Sleep & Stress Support.

M

Magnesium citrate

Magnesium bound to citric acid, one of the most widely used forms. Small studies suggest it is absorbed more completely than magnesium oxide. At higher amounts it can loosen stools. Compare the elemental magnesium per serving. Browse Minerals.

Magnesium glycinate

Magnesium bound to the amino acid glycine, also called magnesium bisglycinate. It is popular in evening routines and often chosen by people with sensitive digestion, though research comparing forms is limited. Capsules hold relatively little magnesium, so a serving may be several capsules. Browse Sleep & Stress Support.

Magnesium L-threonate

A newer, more expensive form of magnesium bound to threonic acid. It provides relatively little elemental magnesium per serving, and human research is still limited. Count it toward the 350 mg daily limit for supplemental magnesium like any other form. Browse Minerals.

Magnesium oxide

A compact form of magnesium with a high share of magnesium by weight, so tablets can be small. It is less soluble than citrate or chloride, and it is among the forms most often linked to loose stools. Taking it with food or splitting the amount may help. Browse Minerals.

mcg and mg

Units of weight on supplement labels. A milligram (mg) is one-thousandth of a gram, and a microgram (mcg) is one-thousandth of a milligram. Vitamins such as D, B12 and folate are listed in mcg; minerals such as magnesium and calcium in mg. Always compare like units. See How to read a supplement label.

Melatonin

A hormone the body makes in the evening as part of the sleep-wake cycle. Supplements range from under 1 mg to 10 mg or more and are commonly used for jet lag and schedule changes. It can cause drowsiness; ask a pediatrician before giving it to a child. Browse Sleep & Stress Support.

Methylcobalamin

A form of vitamin B12 that is one of the active forms the body uses. Some people prefer it to cyanocobalamin, though both raise B12 levels. Labels list the form in parentheses, such as "Vitamin B12 (as methylcobalamin)." See cyanocobalamin and browse Vitamins.

Methylfolate

A form of folate, also listed as L-methylfolate or 5-MTHF, that is the main form of folate circulating in the body. It is found in some prenatal and B-complex formulas as an alternative to folic acid. Labels list it in mcg DFE. Browse Women's, Men's & Kids' Health.

Mixed tocopherols

A blend of the vitamin E family members alpha-, beta-, gamma- and delta-tocopherol, as found in foods. The label lists vitamin E in mg of alpha-tocopherol. Mixed tocopherols are also added to oils in small amounts to help keep them fresh. Browse Vitamins.

Multivitamin

A supplement that combines many vitamins and usually minerals in one product. Formulas differ by age and sex, and some leave out iron. A multivitamin can help fill gaps but doesn't replace a varied diet. Add up its nutrients with any single supplements you take. Browse Vitamins.

N

NE (niacin equivalents)

The unit used for niacin (vitamin B3) on Supplement Facts labels. It accounts for niacin the body can make from the amino acid tryptophan. The adult Upper Intake Level for niacin from supplements and fortified foods is 35 mg a day, and high amounts can cause skin flushing.

NSF certification

Programs from NSF that test supplements against a public standard. NSF contents certification checks that label contents match the product and that there are no unsafe levels of specified contaminants. NSF Certified for Sport adds screening for substances banned in sport. Seals apply to specific products. Read our guide to third-party seals.

O

Omega-3 fatty acids

A family of fats the body uses to build cell membranes. The three main ones are ALA from plants and EPA and DHA from fish and algae. There is an Adequate Intake for ALA but no established amount for EPA and DHA. Browse Omega-3 & Fish Oil.

Other ingredients

The list below the Supplement Facts panel showing everything that isn't a dietary ingredient, such as the capsule shell, fillers, flow agents, sweeteners, flavors and colors, in descending order by weight. Check it for gelatin, sugar alcohols and allergens. See How to read a supplement label.

P

Percent Daily Value (%DV)

The share of the Daily Value that one serving provides. More than 100% is common in supplements and isn't automatically a problem, but it is a reason to check the Upper Intake Level and add up other sources. A dagger (†) means no Daily Value has been established. See How to read a supplement label.

Piperine (black pepper extract)

A compound from black pepper often added to turmeric and curcumin supplements because it increases how much curcumin is absorbed. It can also change how the body processes some medications. Talk to your doctor or pharmacist before using piperine-containing products with any medication. See turmeric and curcumin.

Plant protein

Protein powders made from pea, soy, rice, hemp or a blend. They suit people who avoid dairy. Single-plant proteins can be lower in some essential amino acids, which is why many products blend sources. Check grams of protein per scoop and the allergen statement. Browse Protein & Sports Nutrition.

Postbiotic

A preparation of inactivated microorganisms or their components, rather than live bacteria. Postbiotics are a newer and still-developing category, so labels and research vary. Because the organisms are not alive, CFU counts don't apply. See probiotic and prebiotic.

Prebiotic

A fiber or other compound, such as inulin, that feeds the beneficial bacteria already living in your gut. Prebiotics are found in onions, garlic, asparagus, bananas and whole grains, and in some supplements. Increase them gradually, since they can cause gas. Browse Probiotics & Digestive Health.

Probiotic

Live microorganisms, mostly bacteria and some yeasts, found in some fermented foods and supplements. Labels should name each strain in full and state the CFU count. People with a weakened immune system should talk to their doctor before using probiotics. Browse Probiotics & Digestive Health.

Proprietary blend

A named mix of ingredients for which the label must show only the total weight of the blend, not the amount of each ingredient. Ingredients are listed in descending order by weight. Blends make it harder to compare products or know how much of one ingredient you get. See How to read a supplement label.

R

RAE (retinol activity equivalents)

The unit used for vitamin A on Supplement Facts labels. It accounts for the different activity of preformed vitamin A and beta-carotene. The adult Upper Intake Level of 3,000 mcg RAE a day applies to preformed vitamin A only. See beta-carotene and retinyl palmitate.

Recommended Dietary Allowance (RDA)

The average daily amount of a nutrient that meets the needs of nearly all healthy people in a given age and sex group. RDAs are published by the National Academies and summarized by the NIH Office of Dietary Supplements. For example, the adult RDA for vitamin D is 600 IU (15 mcg), or 800 IU after age 70.

S

Serving size

The amount of a product that all numbers on the Supplement Facts panel refer to, such as two capsules or one scoop. If you take less or more than one serving, the amounts change accordingly. Always check it before comparing products. See How to read a supplement label.

Softgel

A soft, sealed gelatin or plant-based shell that holds oils, such as fish oil, vitamin D or CoQ10. Softgels protect oils from air and make fat-soluble nutrients easy to take. Store them away from heat, which can make them stick together or leak.

Spirulina

A blue-green alga (a cyanobacterium) sold as powders and tablets. Because algae can pick up contaminants from where they grow, look for brands that describe their contaminant testing. Spirulina is a food-based source of protein and pigments. Browse Greens & Superfoods.

Strain

A specific, identifiable line within a microbial species, shown as a code after the genus and species, such as GG in Lacticaseibacillus rhamnosus GG. Research is done on specific strains, and results for one strain don't automatically apply to another. Browse Probiotics & Digestive Health.

Structure/function claim

A statement describing how a nutrient or ingredient affects the normal structure or function of the body, such as "calcium helps support healthy bones." Supplements may make these statements with the FDA disclaimer, and the company must notify the FDA. Disease claims are not allowed. See FDA disclaimer.

Supplement Facts panel

The required label on every dietary supplement, set out in FDA rules at 21 CFR 101.36. It shows the serving size, the amount and % Daily Value of each dietary ingredient, and any proprietary blends, with other ingredients listed below. Read our How to read a supplement label guide.

Sustained release

A tablet or capsule designed to release its contents gradually over several hours, also called extended or time release. It is common for vitamin C, niacin and melatonin. Swallow it whole, and don't crush or split it unless the label says you can.

T

Tamper-evident seal

A seal, such as a foil inner seal or a shrink band around the cap, that shows whether the package has been opened. Check it before use, and don't use a product with a broken or missing seal. Unopened products with intact seals are eligible for free 30-day returns. See Returns & refunds.

Third-party testing

Testing or auditing by an organization independent of the manufacturer, such as USP, NSF or LGC. Programs usually check that a product contains what the label says and isn't contaminated with specified substances. A seal doesn't show that a product works or suits you. Read our guide to third-party seals.

Triglyceride and ethyl ester forms

Two chemical forms of omega-3 in fish oil. Natural fish oil is mostly triglycerides. Concentrated oils are often made as ethyl esters, and some are converted back into re-esterified triglycerides. Either form is usually taken with a meal that contains fat. See fish oil.

Turmeric and curcumin

Turmeric is a root used as a spice; curcumin is the main group of compounds in it, called curcuminoids. Extracts are often standardized to a percentage of curcuminoids, and some add piperine. Talk to your doctor or pharmacist if you take blood thinners or other medications. Browse Herbs & Botanicals.

U

Upper Intake Level (UL)

The highest daily intake of a nutrient that is unlikely to cause harm for most people. Examples for adults include 4,000 IU (100 mcg) of vitamin D, 2,000 mg of vitamin C, 40 mg of zinc and 350 mg of supplemental magnesium. Count every source. See Supplement safety.

USP Verified Mark

A seal from U.S. Pharmacopeia showing that a specific product contains the listed ingredients in the declared amounts, doesn't contain harmful levels of specified contaminants, breaks down properly and was made under cGMP. It doesn't show that a product works. Read our guide to third-party seals.

V

Vegetarian capsule

A capsule shell made from plant material, usually hypromellose (HPMC) or pullulan, instead of gelatin. The shell type is listed under other ingredients. A plant-based shell doesn't make the whole product vegetarian, so check the full label if that matters to you. See capsule.

Vitamin D2 and D3

The two forms of vitamin D in supplements. D2 (ergocalciferol) comes from plant or yeast sources; D3 (cholecalciferol) is the form the skin makes and usually comes from lanolin or lichen. Both raise blood levels of vitamin D, and D3 tends to raise them more and for longer. See our vitamin D in winter guide.

Vitamin K1 and K2 (MK-4, MK-7)

Vitamin K1 (phylloquinone) comes mainly from leafy greens. Vitamin K2 (menaquinones) is found in fermented foods and some animal foods; MK-4 and MK-7 are the forms most used in supplements. Vitamin K can affect how warfarin works, so talk to your doctor or pharmacist first. Browse Vitamins.

W

Water-soluble vitamins

Vitamin C and the eight B vitamins, which dissolve in water. The body stores less of them than fat-soluble vitamins, but very high intakes can still cause problems; several have Upper Intake Levels, such as vitamin B6 and niacin. See fat-soluble vitamins and browse Vitamins.

Whey protein concentrate and isolate

Two forms of protein from milk. Concentrate contains some lactose and fat; isolate is filtered further for a higher share of protein and less lactose. Both are complete proteins and contain milk allergens, so check the allergen statement. Browse Protein & Sports Nutrition.

Sources

• NIH Office of Dietary Supplements: Dietary Supplements, What You Need to Know
• NIH Office of Dietary Supplements: Nutrient Recommendations and Databases
• FDA: Dietary Supplement Labeling Guide
• FDA: Daily Value on the Nutrition and Supplement Facts Labels
• FDA: Dietary Supplements
• eCFR: 21 CFR 101.36, Nutrition labeling of dietary supplements
• eCFR: 21 CFR Part 111, Current Good Manufacturing Practice for Dietary Supplements
• MedlinePlus: Dietary Supplements
• NCCIH: Using Dietary Supplements Wisely
• USP: Verified Mark
• NSF Certified for Sport

This glossary is for general education and isn't a substitute for advice from your doctor, pharmacist or registered dietitian. Talk to your doctor or pharmacist before starting a supplement, especially if you're pregnant or nursing, take medication, or have a medical condition.

†These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.