Most people know that B vitamins are important, particularly for energy. But what do they actually do, where do they come from, and can you still develop low levels even if you eat a varied diet?
B vitamins help the body turn food into usable energy, maintain the nervous system, produce healthy blood cells and make new DNA. Although they are grouped together, each one performs its own distinct functions.
What are B vitamins?
The B-vitamin family consists of eight vitamins. You may recognise some by their common names, such as folate, biotin or niacin, while others are better known by their vitamin numbers.
| Common name | Also known as |
|---|---|
| Vitamin B1 | Thiamin (formerly thiamine) |
| Vitamin B2 | Riboflavin |
| Vitamin B3 | Niacin (nicotinic acid and nicotinamide) |
| Vitamin B5 | Pantothenic acid |
| Vitamin B6 | Pyridoxine, pyridoxal and pyridoxamine |
| Vitamin B7 | Biotin (sometimes called vitamin H) |
| Vitamin B9 | Folate (natural forms) and folic acid (synthetic form) |
| Vitamin B12 | Cobalamin (including methylcobalamin, adenosylcobalamin, hydroxocobalamin and cyanocobalamin) |
What do B vitamins actually do?
Several B vitamins act as coenzymes, or are used to make coenzymes. These are small helper molecules that allow enzymes to carry out essential chemical reactions. Their roles are different but closely connected, particularly in energy metabolism, brain function, blood formation and DNA production.1
They help release energy from food
B vitamins are often described as “energy vitamins”, but they do not contain calories and do not stimulate the body in the way caffeine does.
Instead, vitamins B1, B2, B3, B5, B6, biotin and B12 help the body process carbohydrates, fats and proteins. This allows the energy stored in food to be converted into forms that cells can use.1,2
Correcting a genuine deficiency may help with associated tiredness or weakness. However, taking more B vitamins than the body needs does not necessarily make it produce more energy.
They support the brain and nervous system
The brain uses a substantial amount of energy and depends on a continuous supply of nutrients. Several B vitamins also help produce or process the chemical messengers used by nerve cells.
Vitamins B1, B2, B3, B6, biotin and B12 all contribute in different ways to normal nervous system function. Vitamin B6 is involved in the metabolism of amino acids used to make neurotransmitters, while vitamin B12 is particularly important for the development and maintenance of the nervous system.1,2
This does not mean that a B complex acts as an instant cognitive stimulant. Rather, an adequate supply helps support the underlying biological processes on which the brain and nerves depend.
They help make healthy blood cells
Red blood cells transport oxygen around the body and must be continually replaced.
Vitamin B6 helps the body produce haemoglobin, the oxygen-carrying protein inside red blood cells. Folate and vitamin B12 are needed for normal blood formation and the production of new cells.2
A significant deficiency of folate or vitamin B12 can interfere with red blood cell development and may cause megaloblastic anaemia.
They support DNA synthesis and cell division
Before a cell divides, it must make an accurate copy of its DNA. Folate is needed to produce some of DNA’s essential building blocks, while vitamin B12 helps the body use folate normally.
These functions are particularly important in tissues that regularly produce new cells, including the bone marrow. Folate is also especially important before and during early pregnancy because of its role in normal tissue growth and the development of the neural tube.2
Where do B vitamins come from?
B vitamins are found across a broad range of foods. Different foods supply different members of the family, which is one reason dietary variety matters.
| Common food sources | |
|---|---|
| B1 | Sunflower seeds, peas, beans, nuts, wholegrains and pork |
| B2 | Mushrooms, almonds, dairy products, eggs and spinach |
| B3 | Peanuts, mushrooms, wholegrains, poultry, meat and fish |
| B5 | Mushrooms, avocado, sunflower seeds, lentils, eggs and chicken |
| B6 | Chickpeas, potatoes, bananas, oats, peanuts, poultry and fish |
| B7 | Nuts, seeds, mushrooms, sweet potatoes, legumes and eggs |
| B9 | Leafy green vegetables, broccoli, peas, beans, chickpeas, citrus fruits and liver |
| B12 | Fish, shellfish, meat, eggs and dairy products |
Frequently asked questions
Can you have low vitamin B12 levels even if you eat meat?
Yes. Eating meat, fish, eggs or dairy products can provide vitamin B12, but intake is only one part of the picture. The body must also be able to release B12 from food and absorb it through the digestive system.
Autoimmune gastritis, historically often associated with the term pernicious anaemia, can reduce the production of intrinsic factor, a protein needed for normal B12 absorption. Crohn’s disease, coeliac disease, gastrointestinal surgery and other digestive problems may also interfere with absorption.5
Certain medicines can affect B12 status too. The Medicines and Healthcare products Regulatory Agency considers reduced B12 levels a common side effect of metformin, with risk increasing at higher doses and with longer treatment. Medicines that reduce stomach acid may also be a risk factor.5,6
Someone can therefore consume enough B12 on paper but still develop low levels because their body cannot absorb it effectively.
Who may be at greater risk of low B-vitamin levels?
The risk factors depend on the particular vitamin. They may include:
- People following restrictive or very low-variety diets
- Vegans and some vegetarians, particularly in relation to vitamin B12
- Older adults, who may absorb B12 less efficiently
- People with gastrointestinal conditions or previous digestive surgery
- People taking metformin or certain medicines that reduce stomach acid
- People with prolonged heavy alcohol consumption, particularly in relation to thiamin
- People with low overall food intake
- Women who are pregnant, planning pregnancy or could become pregnant, particularly in relation to folate
Being in one of these groups does not mean that someone is deficient. It simply means that diet, absorption or individual requirements may deserve closer attention.
In the UK National Diet and Nutrition Survey for 2019 to 2023, low red-blood-cell folate was found in 4% of adults aged 19 to 64 and 7% of women of childbearing age.7
What are the possible signs of a B-vitamin deficiency?
Possible symptoms vary according to the vitamin and the severity and duration of the deficiency. They may include:
- Persistent tiredness or weakness
- Shortness of breath
- A sore or red tongue
- Mouth ulcers
- Poor concentration or memory changes
- Pins and needles or numbness
- Problems with balance or coordination
These symptoms are not specific to B-vitamin deficiencies and can have many other causes. Vitamin B12 deficiency can also occur without obvious anaemia, so symptoms and a standard blood count alone cannot always rule it out.5,6
Persistent, unexplained or neurological symptoms should be assessed by an appropriately qualified healthcare professional.
Why choose a food-sourced B Complex?
The eight B vitamins have separate functions, but many work within connected pathways. For example, several are involved in releasing energy from food, while folate, B6 and B12 interact in processes involving blood formation, amino acid metabolism and homocysteine.
This is why many people choose a complete B complex rather than selecting individual B vitamins. A well-designed complex offers a convenient and consistent way to obtain the full family, without having to manage several separate products.
Some people prefer food-source or wholefood-derived complexes because the nutrients come from recognisable food ingredients and may be supplied alongside naturally occurring plant compounds and other co-nutrients from those ingredients. A number of studies suggest these natural complexes may offer distinct physiological advantages over synthetic alternatives.
For instance, research published in the Journal of Healthcare Engineering9 noted that while short-term cellular uptake was similar, participants taking natural food-source B vitamins appeared to maintain more sustained serum levels of cobalamin (B12) and prolonged antioxidant activity after supplementation stopped. This has led some researchers to suggest that natural structures might be retained by tissue for longer periods.
Nutrition researchers are continuing to study the food matrix: the physical and chemical environment surrounding nutrients in a food or food-derived ingredient. The food matrix can influence how nutrients are released during digestion and subsequently absorbed and utilised by the body.3,8
Overview
B vitamins help the body use the energy in food, support normal brain and nervous system function, make healthy blood cells and produce new DNA.
While many people can obtain them through a varied diet, low levels may occur because of restricted intake, increased requirements, digestive conditions, ageing, medicines that affect absorption or simply differences in individual biology. The way nutrients are digested, absorbed, metabolised and utilised can vary considerably from one person to another.
A complete B complex offers a convenient way to obtain all eight vitamins together. Food-source complexes may particularly appeal to people who prefer nutrients derived from recognisable food ingredients and provided within a broader food-derived matrix.
References
- Kennedy DO. B vitamins and the brain: mechanisms, dose and efficacy: a review. Nutrients. 2016;8(2):68. doi:10.3390/nu8020068
- National Health Service. B vitamins and folic acid. Accessed 30 July, 2026. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
- Chungchunlam SMS, Moughan PJ. Comparative bioavailability of vitamins in human foods sourced from animals and plants. Crit Rev Food Sci Nutr. 2024;64(31):11590-11625. doi:10.1080/10408398.2023.2241541
- Watanabe F, Yabuta Y, Bito T, Teng F. Vitamin B12-containing plant food sources for vegetarians. Nutrients. 2014;6(5):1861-1873. Accessed 30 July, 2026. doi:10.3390/nu6051861
- National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management. NICE guideline NG239. Published March 6, 2024. Accessed 30 July, 2026. https://www.nice.org.uk/guidance/ng239
- Medicines and Healthcare products Regulatory Agency. Metformin and reduced vitamin B12 levels: new advice for monitoring patients at risk. Published June 20, 2022. Accessed 30 July, 2026. https://www.gov.uk/drug-safety-update/metformin-and-reduced-vitamin-b12-levels-new-advice-for-monitoring-patients-at-risk
- Office for Health Improvement and Disparities. National Diet and Nutrition Survey 2019 to 2023: report. Published June 11, 2025. Accessed July 30, 2026. https://www.gov.uk/government/statistics/national-diet-and-nutrition-survey-2019-to-2023/national-diet-and-nutrition-survey-2019-to-2023-report
- Aguilera JM. Food matrices as delivery units of nutrients in processed foods. J Food Sci. 2025;90(2):e70049. Accessed 30 July, 2026. doi:10.1111/1750-3841.70049
- Lindschinger M, Tatzber F, Schimetta W, et al. A Randomized Pilot Trial to Evaluate the Bioavailability of Natural versus Synthetic Vitamin B Complexes in Healthy Humans and Their Effects on Homocysteine, Oxidative Stress, and Antioxidant Levels. Oxid Med Cell Longev. 2019;2019:6082613. Published 2019 Dec 12. Accessed 30 July, 2026. doi:10.1155/2019/6082613
Important information: This article was written in collaboration with nutrition specialists and is provided for general educational purposes only. It does not constitute medical advice and should not be used as a substitute for advice, diagnosis or treatment from a qualified healthcare professional.
