What Are Vitamins? The 13 Types, Supplement Label Units and Upper Limits
supmane Editorial Team · Published
Vitamins are substances the body needs for normal cell function, growth and development, and there are 13 essential vitamins. In the United States, the National Academies of Sciences, Engineering, and Medicine sets the Dietary Reference Intakes (DRIs), which include how much of each vitamin to get and the most you can take without likely harm.
1. Fat-soluble vs. water-soluble vitamins
The 13 vitamins split into 4 fat-soluble vitamins and 9 water-soluble vitamins. Fat-soluble vitamins are stored in the body, so too much can build up, while extra amounts of water-soluble vitamins mostly leave the body in urine.
| Group | Vitamins | Dissolves in | Extra amounts | Has a US upper limit |
|---|---|---|---|---|
| Fat-soluble (4) | Vitamins A, D, E and K | Fat | Stored in the liver, fatty tissue and muscles, so they can build up | Vitamins A, D and E |
| Water-soluble (9) | The B vitamins (8) and vitamin C | Water | Not stored (except vitamin B12, which the liver can store); extra amounts leave in urine | Niacin (B3), vitamin B6, folate (B9) and vitamin C |
Storage and excretion follow MedlinePlus (US National Library of Medicine). Upper limits are the Tolerable Upper Intake Levels (ULs) of the National Academies. Some water-soluble vitamins also have a UL.
2. The 13 vitamins
The 8 water-soluble vitamins other than vitamin C are called the B vitamins. B3, B5, B7 and B9 usually go by their names niacin, pantothenic acid, biotin and folate, and the DRIs use those names.
| Vitamin | Group | Other names (chemical names) | Ingredients table |
|---|---|---|---|
| Vitamin A | Fat-soluble | Retinol | Open |
| Vitamin D | Fat-soluble | Cholecalciferol (D3), ergocalciferol (D2) | Open |
| Vitamin E | Fat-soluble | Tocopherol | Open |
| Vitamin K | Fat-soluble | Phylloquinone (K1), menaquinones (K2) | Open |
| Vitamin B1 | Water-soluble (B vitamin) | Thiamin | Open |
| Vitamin B2 | Water-soluble (B vitamin) | Riboflavin | Open |
| Vitamin B3 | Water-soluble (B vitamin) | Niacin (nicotinic acid, nicotinamide) | Open |
| Vitamin B5 | Water-soluble (B vitamin) | Pantothenic acid | Open |
| Vitamin B6 | Water-soluble (B vitamin) | Pyridoxine, pyridoxal, pyridoxamine | Open |
| Vitamin B7 | Water-soluble (B vitamin) | Biotin | Open |
| Vitamin B9 | Water-soluble (B vitamin) | Folate (folic acid) | Open |
| Vitamin B12 | Water-soluble (B vitamin) | Cobalamin | Open |
| Vitamin C | Water-soluble | Ascorbic acid | Open |
“Open” takes you to the row of the ingredients table that lists the ingredients labels use for that vitamin. Our ingredients table also lists NMN and NR, NAD precursors related to niacin, under vitamins (Open).
3. Label units and conversions
For some vitamins, how the amount is counted depends on the form. US labels list vitamin A in mcg RAE, vitamin E in mg (alpha-tocopherol) and folate in mcg DFE, so amounts from different forms can be compared.
| Vitamin | Forms (natural, synthetic, etc.) | Weight unit | IU | Equivalents (RAE, NE, DFE) |
|---|---|---|---|---|
| Vitamin A | Retinol (preformed) and beta-carotene (the body turns it into vitamin A) | mcg | 1 IU retinol = 0.3 mcg RAE | RAE (retinol activity equivalents): 1 mcg retinol = 1 mcg RAE. Beta-carotene: 2 mcg from supplements or 12 mcg from food = 1 mcg RAE |
| Vitamin D | — | mcg | 1 mcg = 40 IU | — |
| Vitamin E | Natural (d-alpha-tocopherol) and synthetic (dl-alpha-tocopherol) | mg | Natural: 1 IU = 0.67 mg. Synthetic: 1 IU = 0.45 mg | — |
| Vitamin K | — | mcg | — | — |
| Vitamin B1 | — | mg | — | — |
| Vitamin B2 | — | mg | — | — |
| Vitamin B3 (niacin) | Nicotinic acid and nicotinamide | mg | — | NE (niacin equivalents): 1 mg niacin = 1 mg NE (60 mg tryptophan = 1 mg NE) |
| Vitamin B5 (pantothenic acid) | — | mg | — | — |
| Vitamin B6 | — | mg | — | — |
| Vitamin B7 (biotin) | — | mcg | — | — |
| Vitamin B9 (folate) | Food folate and folic acid (in supplements) | mcg | — | DFE (dietary folate equivalents): 1 mcg folic acid = 1.7 mcg DFE (1 mcg food folate = 1 mcg DFE) |
| Vitamin B12 | — | mcg | — | — |
| Vitamin C | — | mg | — | — |
Conversions follow the US FDA guidance on unit conversions. IU means international units. US labels list vitamin D in mcg, and may also show the IU amount in parentheses. The “forms” column lists vitamins whose conversion depends on the form. The DRIs count vitamin A, niacin and folate in the same RAE, NE and DFE units.
4. Too little, too much and upper limits
Too little of a vitamin can cause deficiency, and too much of some vitamins can cause health problems. To help people avoid getting too much, the DRIs set Tolerable Upper Intake Levels (ULs) for 7 vitamins: A, D, E, C, niacin (B3), B6 and folate (B9).
| Vitamin | Too little | Too much | Upper limit (adults, per day) |
|---|---|---|---|
| Vitamin A | Night blindness and xerophthalmia (damage to the cornea); dry, scaly skin | Can build up in the body and cause serious health problems. Large doses during pregnancy can cause birth defects | 3,000 mcg RAE (preformed vitamin A only; not beta-carotene) |
| Vitamin D | Rickets (children) and osteomalacia (adults) | Too much calcium in the blood (nausea, vomiting, weakness, kidney stones, kidney damage and more) | 100 mcg (4,000 IU) |
| Vitamin E | Rare; in people who cannot absorb fat well, nerve damage (peripheral neuropathy), ataxia and more | High-dose supplements might increase the risk of bleeding in the brain (hemorrhagic stroke) | 1,000 mg (any form of supplemental alpha-tocopherol) |
| Vitamin K | Very rare; bruising and bleeding | Not enough data to set an upper limit | None |
| Vitamin B1 | Weakness, fatigue and nerve damage; beriberi. Severe deficiency can cause Wernicke disease and Korsakoff syndrome | No known poisoning from too much thiamin | None |
| Vitamin B2 | Severe deficiency: mouth or lip sores, sore throat, skin problems, anemia | Extra amounts leave the body in urine; no known poisoning | None |
| Vitamin B3 (niacin) | Pellagra (digestive problems, inflamed skin, poor mental function) | Flushing (warmth, redness, itching). Too much can also cause liver damage, peptic ulcers, high blood sugar and skin rashes | 35 mg (from supplements, fortified foods or both) |
| Vitamin B5 (pantothenic acid) | Very rare; tingling in the feet | Large doses: possibly diarrhea | None |
| Vitamin B6 | Uncommon in the US; confusion, depression, mouth and tongue sores, peripheral neuropathy | Large doses: numbness, sensory changes, difficulty coordinating movement | 100 mg |
| Vitamin B7 (biotin) | Dermatitis, glossitis, muscle pain, hair loss, brittle nails | No known toxic symptoms | None |
| Vitamin B9 (folate) | Megaloblastic anemia | High amounts of folic acid can hide a vitamin B12 deficiency | 1,000 mcg (from supplements, fortified foods or both) |
| Vitamin B12 | Anemia, numbness or tingling in the arms and legs, loss of balance, weakness | Low potential for toxicity | None |
| Vitamin C | Scurvy (bleeding gums, easy bruising, slow wound healing and more) | More than 2,000 mg a day can cause stomach upset and diarrhea, and rarely kidney stones | 2,000 mg |
Upper limits are the National Academies' Tolerable Upper Intake Levels for adults (19 and older): the highest daily intake likely to pose no risk of adverse health effects for almost everyone. Unless noted, they cover total intake from food, water and supplements. “None” means no UL was set because there was not enough data; extra caution may still be warranted above recommended intakes. Examples of too little and too much are from MedlinePlus and the NIH Office of Dietary Supplements.
5. What to check before using a supplement
Before using a supplement, check that you are not getting the same vitamin twice, and that it suits any medicines you take and your health.
| Situation | What to check |
|---|---|
| Using a multivitamin with single-vitamin supplements | The same vitamin can be in more than one product. Add up the amounts on the labels and compare the total with the upper limit |
| Getting a vitamin from both food and supplements | Count what you get from food too. The upper limits for vitamin E, niacin and folate cover only the forms in supplements and fortified foods |
| Taking medicines | Some vitamins interact with medicines. For example, high doses of vitamin E taken with anticoagulants such as warfarin or with antiplatelet drugs might increase the risk of bleeding (NIH). If you take warfarin, keep your vitamin K intake about the same every day (MedlinePlus) |
| Pregnant, possibly pregnant or breastfeeding | Don't take high doses of vitamin A supplements (3,000 mcg RAE [10,000 IU] or more a day) (NIH) |
| Health concerns or upcoming surgery | Tell your health care provider about any supplements you use, and don't take more than the label recommends (MedlinePlus) |
6. Primary sources
We checked the facts and numbers in this article against these sources.
| Document | Publisher / what we used |
|---|---|
| Summary Tables: Dietary Reference Intakes | National Academies (Institute of Medicine, 2011). Tolerable Upper Intake Levels for vitamins and their footnotes |
| Vitamins | MedlinePlus (US National Library of Medicine). Fat-soluble and water-soluble vitamins |
| Dietary Supplements | MedlinePlus. How to take a supplement as safely as possible |
| Vitamin A | MedlinePlus Medical Encyclopedia. Too little and too much |
| Thiamin | MedlinePlus Medical Encyclopedia. Too little and too much |
| Riboflavin | MedlinePlus Medical Encyclopedia. Too little and too much |
| Niacin | MedlinePlus Medical Encyclopedia. Too little and too much |
| Pantothenic acid and biotin | MedlinePlus Medical Encyclopedia. Too little and too much |
| Vitamin B6 | MedlinePlus Medical Encyclopedia. Too little and too much |
| Folic acid in diet | MedlinePlus Medical Encyclopedia. Too little and too much |
| Vitamin B12 | MedlinePlus Medical Encyclopedia. Too little and too much |
| Vitamin C | MedlinePlus Medical Encyclopedia. Too little and too much |
| Vitamin D | MedlinePlus Medical Encyclopedia. Too little and too much |
| Vitamin E | MedlinePlus Medical Encyclopedia. Too little and too much |
| Vitamin K | MedlinePlus Medical Encyclopedia. Too little and too much |
| Vitamin A and Carotenoids: Fact Sheet for Health Professionals | NIH Office of Dietary Supplements |
| Vitamin D: Fact Sheet for Health Professionals | NIH Office of Dietary Supplements |
| Vitamin E: Fact Sheet for Health Professionals | NIH Office of Dietary Supplements |
| Folate: Fact Sheet for Health Professionals | NIH Office of Dietary Supplements |
| Vitamin B12: Fact Sheet for Health Professionals | NIH Office of Dietary Supplements |
| Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels | US FDA (PDF) |