What's in vitamin B complex, and what does each B do?

Vitamin B complex means the eight B vitamins: B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate) and B12 (cobalamin). Each contributes to different normal functions in the body, such as energy metabolism, the nervous system, red blood cell formation and the immune system. All eight are water-soluble.

Each also has its own chemical name, Thai Reference Daily Intake (Thai RDI) and food sources, and several come in more than one form, such as folic acid versus the folate in food, or cyanocobalamin versus methylcobalamin. This article puts all of that in one place. For more detail on particular topics, see How many B vitamins are there, and how do B1 and B2 differ?, What do vitamins B12 and B6 do, and where do they come from? and What Do B Vitamins Do for the Brain and Nerves?

Which vitamins make up vitamin B complex, and what does each one do?

This table brings together each B vitamin's other names, its roles in the body, the foods richest in it and its Thai RDI. The Thai RDI is a single value for the general population aged 3 and over. Food sources are summarised from the fact sheets of the NIH ODS (Office of Dietary Supplements, US National Institutes of Health).

NE stands for niacin equivalents and DFE for dietary folate equivalents; both are explained below.

Different names for the same vitamin

Some B vitamins are more often called by their chemical name than by their number. Biotin is sometimes called B7, and folate is sometimes called B9. The NIH ODS notes that folate was formerly known as folacin, and that niacinamide is another name for nicotinamide.

B12 comes from animal foods

The NIH ODS says vitamin B12 is found in foods of animal origin and is not naturally present in plant foods, but some plant foods are fortified with it, including many breakfast cereals and nutritional yeasts. If you eat a vegetarian or vegan diet, see What do vitamins B12 and B6 do, and where do they come from?

What does vitamin B complex do?

The B vitamins do not all do the same job. Grouping the roles in the table above shows that some functions involve many B vitamins and others only a few.

Energy metabolism

B1 contributes to normal energy metabolism from carbohydrate, and B2, B3, B5, B6, B12 and biotin contribute to normal energy metabolism. Folate is the only one whose roles lie elsewhere. This is covered in more depth in How many B vitamins are there, and how do B1 and B2 differ?

The nervous system and the brain

B1, B2, B3, B6, B12 and biotin contribute to the normal function of the nervous system. B12 is the only one whose role also covers the normal function of the brain. B5 contributes to the normal synthesis and metabolism of some neurotransmitters. For how this works in the body, see What Do B Vitamins Do for the Brain and Nerves?

Red blood cells

B6 and folate contribute to normal red blood cell formation, B12 contributes to the normal synthesis of substances needed for red blood cell formation, and B2 contributes to the maintenance of normal red blood cells.

The immune system

Among the B vitamins, three contribute to the normal function of the immune system: B6, B12 and folate.

Skin, mucous membranes and other roles

B2, B3 and biotin contribute to the maintenance of normal skin and mucous membranes. Biotin also covers hair, and B2 covers vision and iron metabolism. B6 contributes to normal protein and glycogen metabolism, folate to normal amino acid synthesis, and B5 to steroid hormones and vitamin D.

What does "normal" mean here?

It refers to the body's ordinary functioning. B vitamins are part of what the body uses to carry out these functions. It does not mean that getting more makes anything work better; getting more than you need adds no extra benefit.

Are there 8 or 10 B vitamins? Are choline and inositol B vitamins?

There are eight B vitamins. The Thai RDIs include all eight, and the UK's NHS gives information on the same eight: thiamin, riboflavin, niacin, pantothenic acid, vitamin B6, biotin, folate and folic acid, and vitamin B12.

Why some sources count 10

Some sources also count choline and inositol as B vitamins, which gives a total of 10. Neither is on the list of eight used by the Thai RDIs and the NHS. On that list the numbers skip: there is no B4, B8, B10 or B11.

Choline

The NIH ODS describes choline as an essential nutrient rather than a vitamin. It says the liver makes some choline, but not enough to meet the body's needs, so it also has to come from food. There is no Thai RDI for choline.

Inositol

Inositol is not on the list of B vitamins used by the Thai RDIs or the NHS, and there is no Thai RDI for it.

Some B vitamins depend on each other

One reason the B vitamins are often discussed together is that some rely on others in the body. The NIH ODS says turning the amino acid tryptophan into niacin requires FAD, an active form of B2, and that converting B6 into its coenzyme form needs FMN, another form of B2.

What should I eat to get all the B vitamins?

B vitamins are spread across many food groups, and no single food is rich in all of them, so eating a variety of foods brings in several at once.

Everyday foods that contain B vitamins

Grouping the food sources in the table above (NIH ODS):

• Brown rice and other whole grains contain B1, B3 and B5
• Pork, chicken, beef and fish contain B1, B3, B5, B6 and B12
• Eggs and milk contain B2 and B12, and eggs also contain biotin and folate
• Liver and other organ meats contain B2, B5, B6, biotin and folate
• Beans, seeds and dark green leafy vegetables: beans and nuts contain B3, biotin and folate, and dark leafy greens contain folate

Can most people get enough from food?

The UK's NHS says people should be able to get each of the B vitamins they need from a varied and balanced diet. It also notes that the bacteria that live naturally in the bowel can make vitamin B6 and biotin. For B12, the NIH ODS says it occurs naturally in animal foods and in plant foods fortified with it.

What other names do the B vitamins go by?

Many B vitamins are not a single compound but a family of related ones, and in the body they are turned into working forms with names of their own. The table summarises these names, according to the NIH ODS.

The working forms are explained in more detail in What Do B Vitamins Do for the Brain and Nerves?

B6 is a family of compounds

The NIH ODS says vitamin B6 is the general name for six compounds: pyridoxine, pyridoxal and pyridoxamine, and their phosphate forms.

The names of B12 (cobalamins)

The NIH ODS says compounds with vitamin B12 activity are called cobalamins because they contain the mineral cobalt. Hydroxocobalamin and cyanocobalamin have to be converted to methylcobalamin or 5-deoxyadenosylcobalamin before they become active.

B3 has several names

The NIH ODS says niacin is the general name for nicotinic acid, nicotinamide (also called niacinamide) and related compounds. The body can also make some niacin from the amino acid tryptophan, which is why daily amounts are given in niacin equivalents (NE).

What is the difference between folic acid and folate?

The NIH ODS says folate is the general name for vitamin B9, covering the folate found naturally in food and the folate in dietary supplements and fortified foods, including folic acid. Folic acid is the synthetic form added to foods and dietary supplements.

What DFE means

Dietary folate equivalents (DFE) are the unit the NIH ODS uses to count food folate and folic acid together on the same scale. So the Thai RDI for folate of 400 mcg DFE counts both food folate and folic acid. For more about folate itself, see What is folate, and what does it do in the body?

5-MTHF

The NIH ODS says folate in food is in the tetrahydrofolate (THF) form and that the main form of folate in plasma is 5-MTHF.

Is taking too much vitamin B harmful?

Under the US values published by the NIH ODS, three B vitamins have a tolerable upper intake level for adults.

Niacin and skin flushing

The NIH ODS says nicotinic acid in amounts beyond the body's needs can cause flushing in some people, with the skin on the face, arms and chest turning red, along with burning, tingling or itching. The niacin upper limit is based on this effect and applies to both forms of supplemental niacin.

Large amounts of B6 over a long time

The NIH ODS says B6 from food has not been reported to cause harm, but very large amounts of pyridoxine taken over a long period can affect the nerves. The NIH ODS also notes that in 2023 the European Food Safety Authority (EFSA) set a European upper limit for B6 of 12 mg a day for adults.

Biotin and blood tests

The NIH ODS says no upper limit has been set for biotin because there is no evidence in humans that it is toxic at high intakes, but taking large amounts of biotin can make some laboratory test results falsely high or falsely low. If you have been getting large amounts of biotin, tell your doctor before a blood test.

Why can B vitamins turn urine bright yellow?

The bright yellow colour comes from vitamin B2, riboflavin.

Riboflavin is yellow

The NIH ODS says riboflavin is yellow and glows under ultraviolet light. The body stores only small amounts of riboflavin; any excess is either not absorbed or leaves in urine.

Why can urine turn bright yellow?

The Harvard T.H. Chan School of Public Health says an excess of riboflavin, usually from supplements, can make urine bright yellow. No US upper limit has been set for riboflavin, because harmful effects from high intakes have not been reported (NIH ODS).

What does it mean that B vitamins are water-soluble?

All eight B vitamins dissolve in water, which matters both for the body and for food.

The body stores little, so you need them every day

The NIH ODS says the body excretes excess thiamin in urine and that thiamin does not stay in the body for long, so a continuous supply from food is needed; riboflavin is stored only in small amounts in the liver, heart and kidneys. The NHS likewise says thiamin, riboflavin, niacin and pantothenic acid cannot be stored in the body, so you need them in your diet every day.

B12 is the exception

The NIH ODS says the body stores about 1 to 5 mg of vitamin B12, or roughly 1,000 to 2,000 times the amount typically consumed in a day.

Cooking and processing reduce them

The NIH ODS describes these losses:

• B1 Thiamin dissolves into cooking water, so a lot is lost if the water is thrown away, and heat reduces it: bread, for example, has 20% to 30% less thiamin than its raw ingredients.
• B2 Boiling loses about twice as much riboflavin into the cooking water as steaming or microwaving does, and light breaks riboflavin down quickly.
• B5 Food processing can reduce pantothenic acid by 20% to almost 80%.

From this, steaming, or eating the broth along with a soup or curry, loses less B1 and B2 to water than boiling and pouring the water away.

Who should talk to a doctor or pharmacist?

People who take regular medication

Some medicines can affect certain B vitamins. If you take medication regularly, ask a doctor or pharmacist.

Pregnant and breastfeeding women

If you are pregnant, breastfeeding or take regular medication, speak to a doctor or pharmacist before taking dietary supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.