The B Vitamins: What the Eight Do, How They Work Together and What "B-Complex" Means
What the eight B vitamins do, how they work together, official UK and US amounts, which have safety limits, and what "B-complex" on a label means.
Content last updated . This page has not been medically reviewed.
"B-complex" is a product term, not a nutrient. We did not find a definition of it from the NHS or MedlinePlus pages read for this page, so the Supplement Facts panel is the only reliable way to know which B vitamins a product contains and how much. See B-complex and calcium-plus-D products.
Choline is often grouped with the B vitamins but is not one of the eight. MedlinePlus lists it as a vitamin-like nutrient. [2] See choline.
Evidence labels used on this page: established nutritional role / deficiency treatment, insufficient evidence.
What each one does
| B vitamin | What the NHS says it helps with | Profile |
|---|---|---|
| Thiamin (B1) | Releasing energy from food; keeping the nervous system healthy. [3] | More about Thiamin (B1) → |
| Riboflavin (B2) | Keeping skin, eyes and the nervous system healthy; releasing energy. [3] | More about Riboflavin (B2) → |
| Niacin (B3) | Releasing energy; keeping the nervous system and skin healthy. [3] | More about Niacin (B3) → |
| Pantothenic acid (B5) | Helping the body release energy from food, among other functions. [3] | More about Pantothenic acid (B5) → |
| Vitamin B6 | Using and storing energy from protein and carbohydrate; forming hemoglobin. [3] | More about Vitamin B6 → |
| Biotin (B7) | Making fatty acids, needed in very small amounts. [3] | More about Biotin (B7) → |
| Folate (B9) | Forming healthy red blood cells; lowering the risk of neural tube defects in pregnancy. [3] | More about Folate (B9) → |
| Vitamin B12 | Making red blood cells, keeping the nervous system healthy, releasing energy and using folate. [3] | More about Vitamin B12 → |
How they work together
The B vitamins are separate nutrients with separate deficiency problems, but some depend on each other. The NHS says B12 helps the body use folate. [3] MedlinePlus says folate works with B12 and vitamin C to help the body break down, use and create new proteins. [4] A lack of B12 or B6 can cause anemia. [1]This link has a practical side. The NHS says folic acid above 1 mg a day can mask the symptoms of B12 deficiency, which can eventually damage the nervous system if it is not spotted. [3]
Most are not stored, and one is
MedlinePlus says all the B vitamins are water-soluble and not stored in the body, with the exception of B12, which can be stored in the liver for many years. [2] The NHS gives the same message for thiamin, riboflavin and niacin: you need them in your diet every day. [3] Water-soluble does not mean harmless, as the safety table below shows.Official amounts at a glance
These are adult figures from two bodies that set them differently, so the numbers are not identical. They are published reference levels, not personal advice.| Vitamin | NHS, UK (2020): adults 19 to 64 | US RDA (or Adequate Intake) via MedlinePlus, reviewed 2025 |
|---|---|---|
| Thiamin | 0.8 mg women, 1 mg men a day [3] | Women 19 and over 1.1 mg, men 14 and over 1.2 mg a day [5] |
| Riboflavin | 1.1 mg women, 1.3 mg men a day [3] | Women 19 and over 1.1 mg, men 14 and over 1.3 mg a day [6] |
| Niacin | 13.2 mg women, 16.5 mg men a day [3] | Women 14 and over 14 mg, men 14 and over 16 mg a day [7] |
| Pantothenic acid | No UK amount set [3] | 5 mg a day, an Adequate Intake (ages 14 and older) [8] |
| Vitamin B6 | 1.2 mg women, 1.4 mg men a day [3] | Ages 19 to 50: 1.3 mg; over 50: women 1.5 mg, men 1.7 mg a day [9] |
| Biotin | Not clear any is needed from diet [3] | 30 mcg a day, an Adequate Intake (ages 19 and older) [8] |
| Folate | 200 micrograms (mcg) a day [3] | 400 mcg a day (ages 14 and over) [4] |
| Vitamin B12 | About 1.5 mcg a day [3] | 2.4 mcg a day (ages 14 and over) [10] |
The NIH Office of Dietary Supplements pages blocked our download, so US figures here come from MedlinePlus, which reports the same US reference intakes. See RDA, AI, DV and UL for what these terms mean.
Who may need assessment
- People who eat no animal foods: B12 is not found naturally in plant foods. [3] See vegetarian and vegan supplements.
- People who drink heavily: MedlinePlus says thiamin deficiency in the US is most often seen in people who consume too much alcohol. [5]
- Anyone who is or could become pregnant: the NHS recommends a 400 mcg folic acid supplement daily until 12 weeks of pregnancy (UK advice; your own midwife or doctor decides what is right for you). [3] See folic acid in pregnancy.
- Older adults and people with gut conditions: MedlinePlus lists age over 50 and stomach or intestinal conditions as common reasons for low B12. [10]
Please do not decide you are deficient from tiredness alone. Tiredness has many causes; see deficiency testing and its limits. Claims that a B vitamin will "boost energy" in people who are not deficient are covered in B12 and energy claims.
Frequently asked questions
How many B vitamins are there?
MedlinePlus lists eight: thiamine, riboflavin, niacin, pantothenic acid, B6, biotin, B12 and folic acid. [1]
What does B-complex mean?
It is a product description rather than a defined nutrient. We found no definition from the NHS or MedlinePlus pages we read, so check the Supplement Facts panel to see which B vitamins are inside and in what amounts.
Do I need to take all the B vitamins together?
Proper evidence not found. The sources read describe each vitamin's role and a few links between them, such as B12 and folate, but none says that taking them together is better for people who are not deficient. [3]
Is choline a B vitamin?
No. MedlinePlus lists choline as a vitamin-like nutrient, not one of the 13 essential vitamins. [2]
Which B vitamin can cause harm at high amounts?
The NHS names B6 (nerve damage), niacin as nicotinic acid (flushing, liver damage over time) and folic acid (can mask B12 deficiency). [3]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Which B vitamins have safety notes
| Vitamin | What the NHS says about high supplement amounts |
|---|---|
| Thiamin, riboflavin, B12, biotin, pantothenic acid | Not enough evidence to know the effects of high doses. Lack of evidence is not proof of safety. [3] |
| Niacin | High doses of nicotinic acid can cause skin flushes and, over a long time, liver damage. [3] See niacin flush and safety. |
| Vitamin B6 | 200 mg or more a day can cause nerve damage in the arms and legs; it is sometimes permanent. [3] See B6 toxicity. |
| Folic acid | Doses above 1 mg can mask B12 deficiency. [3] |
Safety and talking to a clinician
References
- MedlinePlus (US National Library of Medicine). B Vitamins. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Vitamins. Review date 1/21/2025. Read 2026-10-23.
- NHS (UK). Vitamins and minerals: B vitamins and folic acid. Page last reviewed 3 August 2020. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Folic acid in diet. Review date 2/3/2025. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Thiamin. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Riboflavin. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Niacin. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Pantothenic acid and biotin. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Vitamin B6. Review date 1/21/2025. Read 2026-10-23.
- MedlinePlus Medical Encyclopedia (US National Library of Medicine). Vitamin B12. Review date 1/21/2025. Read 2026-10-23.
- NHS (UK). PMS (premenstrual syndrome). Page last reviewed 18 June 2024. Read 2026-10-23.