In this guide
At a glance
- There are thirteen vitamins: fat-soluble A, D, E, K and water-soluble C and eight B vitamins.
- Deficiency diseases are specific to vitamins; biotin and pantothenic acid deficiency is extremely rare.
- An upper limit (UL) has not been set for every vitamin; US and EU values differ for vitamins B6, E, and C and for niacin.
- “Upper limit not established” does not mean “high doses are safe”; in most cases it describes insufficient data.
- The food sources in the table are the principal sources in the Merck Manual; Türkiye serving values and details are in each vitamin guide.
How many types of vitamins are there?
The Merck Manual divides vitamins into two groups: fat-soluble (A, D, E, and K) and water-soluble (B vitamins and vitamin C). The B vitamins consist of biotin, folate, niacin, pantothenic acid, riboflavin (B2), thiamin (B1), B6, and B12. [1] That makes thirteen vitamins in total; EFSA’s dietary reference values summary report also covers nutrient reference values for each of these vitamins. [4]
The solubility distinction in practice affects three things: absorption, storage, and the consequences of excess intake. The fat-soluble vitamins A, D, E, and K are absorbed in the intestine together with dietary fat and stored in the liver. [3] Water-soluble vitamins, in contrast, have limited storage in the body; the Merck Manual reports that for water-soluble vitamins (other than B12), deficiency can develop after weeks to months of inadequate nutrition, whereas for fat-soluble vitamins and B12, because the body stores them in relatively large amounts, deficiency develops over more than a year. [1] Vitamin K is the exception to this generalization: according to the NIH, compared with the other fat-soluble vitamins it is rapidly broken down and excreted and its tissue stores are relatively low; in newborns, deficiency can be seen in the first weeks. [6] The details of these differences and their exceptions are covered in a separate guide.
Detailed guideFat- and water-soluble vitamins: differences in storage, absorption, and safetyFunction, source, and deficiency disease of the 13 vitamins
The table is compiled from the Merck Manual’s “Sources, Functions, and Effects of Vitamins” table; the food sources are US-based. In the upper limit column, the US values are the National Academies (NASEM) upper limits as reported by the Merck Manual; the EU values are taken from EFSA’s 2025 upper limit summary. [1] [2]
| Vitamin | Main function | Principal food sources | Deficiency disease | Upper limit (UL) |
|---|---|---|---|---|
| Vitamin A (retinol) | Formation of rhodopsin in the retina (vision), epithelial integrity | Preformed A: fish liver oils, liver, egg yolk, butter, dairy products fortified with A. Provitamin carotenoids: dark green and yellow vegetables, carrots, yellow-orange fruits | Night blindness, xerophthalmia, keratomalacia; increase in illness and death in young children | Exists. US: 3,000 µg/day. EFSA: 3,000 µg RE/day (both for preformed A only) |
| Vitamin D (cholecalciferol, ergocalciferol) | Calcium and phosphate absorption, bone mineralization | Production in the skin with UVB light (main source); in the US, fortified dairy products, fish liver oils, fatty fish, liver | Rickets (sometimes with tetany), osteomalacia | Exists. US: 4,000 IU/day. EFSA: 100 µg/day (= 4,000 IU) |
| Vitamin E (tocopherols) | Antioxidant in cell membranes | Vegetable oils, nuts | Red blood cell hemolysis, neurological findings | Exists. US: 1,000 mg/day (supplemental α-tocopherol). EFSA: 300 mg/day |
| Vitamin K (phylloquinone, menaquinones) | Synthesis of clotting factors (prothrombin) and bone proteins | Green leafy vegetables, soy, vegetable oils; intestinal bacteria after the newborn period | Bleeding, osteopenia | Not established. US: could not be determined. EFSA: insufficient data |
| Vitamin B1 (thiamin) | Carbohydrate and amino acid metabolism, nerve and heart muscle function | Whole grains, meat (especially pork and liver), fortified grain products, nuts, legumes, potatoes | Beriberi (peripheral neuropathy, heart failure), Wernicke-Korsakoff syndrome | Not established. US: could not be determined. EFSA: insufficient data |
| Vitamin B2 (riboflavin) | Carbohydrate and protein metabolism, oral mucosa health | Milk, cheese, liver, meat, fish, eggs, fortified grains | Cracked lips (cheilosis), inflammation of the mouth corners, corneal vascularization | Not established. US: could not be determined. EFSA: insufficient data |
| Vitamin B3 (niacin) | Oxidation-reduction reactions, cellular metabolism | Liver, red meat, fish, chicken, legumes, whole or fortified grains | Pellagra (dermatitis, glossitis, digestive and central nervous system disorders) | Exists. US: 35 mg/day (for supplemental niacin only; based on facial flushing). EFSA: separate by form; in adults nicotinamide 900 mg/day, nicotinic acid 10 mg/day (insufficient data in pregnancy and lactation) |
| Vitamin B5 (pantothenic acid) | Coenzyme A synthesis; carbohydrate, protein, and fat metabolism | Animal products, many fruits and vegetables, fortified grains | Extremely rare | Not established. EFSA: insufficient data |
| Vitamin B6 (pyridoxine and related compounds) | Nitrogen (amino acid) metabolism, heme synthesis | Organ meats (liver), whole grains, fish, legumes | Seizures, anemia, neuropathy, seborrheic dermatitis | Exists. US: 100 mg/day. EFSA: 12 mg/day |
| Vitamin B7 (biotin) | Carbohydrate and fatty acid metabolism | Liver, kidney, meat, eggs, milk, fish, dried yeast, sweet potatoes, seeds and nuts | Extremely rare | Not established. EFSA: insufficient data |
| Vitamin B9 (folate, folic acid) | Red blood cell maturation, DNA synthesis, fetal nervous system development | Raw green leafy vegetables, fruits, organ meats, fortified grains and bread | Megaloblastic anemia, neural tube defect, confusion | Exists. US: 1,000 µg/day (folic acid in supplements and fortified foods). EFSA (2023): 1,000 µg/day (sum of folic acid added to food or used in supplements and approved 5-MTHF salts; excluding natural folate in food) |
| Vitamin B12 (cobalamins) | Red blood cell maturation, nerve function, DNA and myelin synthesis | Meat (especially beef, pork, organ meats), chicken, eggs, dairy products, fortified grains, clams, oysters, mackerel, salmon | Megaloblastic anemia, neurological findings (confusion, paresthesia, ataxia) | Not established. US: could not be determined. EFSA: no adverse effect identified |
| Vitamin C (ascorbic acid) | Collagen synthesis, bone and vascular health, wound healing | Citrus fruits, tomatoes, potatoes, broccoli, strawberries, sweet peppers | Scurvy (bleeding, gum inflammation, loose teeth, bone defects) | Exists. US: 2,000 mg/day. EFSA: insufficient data |
Vitamins B2, B3, and B5 do not have a separate guide page; the relationship among these three vitamins and the other B vitamins is covered in the B complex guide.
Detailed guideB complex: eight B vitamins, blend supplements, and high-dose risksConclusions from the table
What does it mean that an upper limit has not been set?
In the Merck Manual’s table, “ND” indicates an upper limit that could not be determined because of insufficient data, and it adds that in this case intake should be limited to food. [1] EFSA also says “insufficient data to derive an upper limit” for vitamins B1, B2, biotin, pantothenic acid, C, and K; for B12 it uses the statement “no adverse effect has been defined.” [2] So there are two different situations: for some vitamins there are no data showing harm from high intake, and for others the scarcity of data prevents setting a limit. Neither means “unlimited safe.”
Why do US and EU upper limits differ?
For vitamin B6, the US limit is 100 mg/day and the EFSA limit is 12 mg/day; for vitamin E, 1,000 mg versus 300 mg; for vitamin C, the US sets 2,000 mg while EFSA reports that there are insufficient data; for niacin, the US gives a single value (35 mg) while EFSA sets separate limits for nicotinic acid (10 mg) and nicotinamide (900 mg). [1] [2] EFSA’s summary states that the B6 and folate upper limits were updated in 2023, the vitamin D limit in 2023, and the vitamin A limit in 2024; and that review of the vitamin E limit is ongoing. [2] On this site, the name of the organization is given next to each value.
Does a deficiency disease show that a supplement is necessary?
No. Deficiency diseases show that a vitamin is necessary for the body; the benefit of an extra supplement in a healthy person who is getting enough is a separate question. The US Preventive Services Task Force reports that, in nonpregnant community-dwelling adults, for the purpose of preventing cardiovascular disease and cancer, the harms of beta-carotene supplementation outweigh the benefits, vitamin E supplementation provides no net benefit, and for multivitamins and other single or paired nutrient supplements, there is insufficient evidence to determine the balance of benefits and harms. [5] The Merck Manual states that vitamin toxicity mostly results from “megadoses” of A, D, C, B6, or niacin. [1]
Details not included in the table
The table is deliberately brief. The same vitamin exists in more than one chemical form (for example, retinol and provitamin carotenoids for A, folate in foods and folic acid in supplements for folate, K1 and K2 for K), and the absorption, unit, and side effects of these forms differ. Upper limits also sometimes apply only to the amount taken from supplements: EFSA notes that for folate and preformed vitamin A the upper limit applies only to specific forms (folic acid added to food or used in supplements and approved 5-MTHF salts; preformed vitamin A). [2] These details are given with their sources in the relevant vitamin guides.
Which vitamin page should be visited?
Starting points by topic are as follows:
- General concepts and reference values: What are vitamins?
- Differences in storage, absorption, and safety: Fat- and water-soluble vitamins
- Which vitamin complaints such as fatigue, hair loss, and numbness are related to: Vitamin deficiency symptoms
- Individual vitamins: D, B12, C, K2, folic acid, A, E, B6, B1, biotin, B complex
- Minerals: magnesium, zinc, iron, calcium, selenium, iodine, potassium
This guide does not recommend personal doses; the reference values and risks of each vitamin are given with their sources in the relevant guide.
Frequently asked questions
What are the types of vitamins?
There are four fat-soluble vitamins (A, D, E, K) and nine water-soluble vitamins: vitamin C and eight B vitamins (B1, B2, niacin, pantothenic acid, B6, biotin, folate, B12). That makes thirteen vitamins in total.
How many B vitamins are there?
The Merck Manual counts eight B vitamins: biotin, folate, niacin, pantothenic acid, riboflavin (B2), thiamin (B1), B6, and B12. A mixture of these eight is sold in supplements under the name "B complex."
Deficiency of which vitamins causes disease?
Deficiency diseases are specific to vitamins: scurvy in vitamin C, beriberi in B1, pellagra in niacin, rickets and osteomalacia in D, night blindness in A, megaloblastic anemia in B12 and folate. Biotin and pantothenic acid deficiency is extremely rare.
Does every vitamin have an upper limit?
No. In the US values reported by Merck, an upper limit has been set for A, C, D, E, B6, niacin, and folate; it has not been set for B1, B2, B12, and K. EFSA's upper limits differ in part; for example, for vitamin C EFSA reports that there are insufficient data.
Sources
- Guideline / review Merck Manual Professional Edition — Overview of Vitamins (Johnson LE; tablo: Sources, Functions, and Effects of Vitamins; Recommended Daily Intakes for Vitamins) (2026)Back to text ↑
- Institution EFSA — Overview on Tolerable Upper Intake Levels as derived by the SCF and the EFSA NDA Panel (sürüm 11, Ağustos 2025; Tablo 3: vitaminler) (2025)Back to text ↑
- Guideline / review Fat-Soluble Vitamins A, D, E, and K: Review of the Literature and Points of Interest for the Clinician (J Clin Med) (2024)Back to text ↑
- Institution EFSA — Dietary Reference Values for nutrients: Summary report (EFSA Supporting Publications) (2017)Back to text ↑
- Institution Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: US Preventive Services Task Force Recommendation Statement. (2022)Back to text ↑
- Guideline / review NIH Office of Dietary Supplements — Vitamin K: Health Professional Fact Sheet (2021)Back to text ↑
Method: Institutional clinical guidance and relevant studies were compared. Each finding is presented with its population, outcome, sources and limitations. Independent medical review has not yet been completed.
This content is for information only and is not medical advice. It does not recommend doses, products or vendors. Talk to your clinician before making any health decision.
