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Help centreVitamin B complex: functions, sources, deficiency and supplements
Written byH&B editorial team
Reviewed byHeeral Tomlinson
Known for energising and balancing both brain and body, these unsung heroes are vital. Unlock the secrets of the vitamin B complex, their roles, sources and why they're essential to your health
Summary
1What’s a vitamin B complex?
A vitamin B complex is the collective name for all eight B vitamins essential for the healthy functioning of the body.
2How much of each B vitamin do I need?
The amount of vitamin B you need depends on your age, sex and other factors, like whether you’re pregnant – so it changes throughout your life.
3Sources of B vitamins in food
Eating a varied, balanced diet should ensure you get enough B vitamins day-to-day. Think fresh fruits, seeds, meat, soybeans, mushrooms and more.
Feeling a little ‘B-wildered’ by all the different B vitamins? You're not alone. Whether you're familiar with some or you just know they're important, the vitamin B complex has a lot more going on than meets the eye. From supporting energy to keeping your brain and body in balance, these vitamins are thought to be the unsung heroes of your health.
If you’re curious about what each one does, how to get enough from your diet and what happens if you’re running low, then let’s break it down and discover why the B complex is a big deal for your wellbeing...
What’s a vitamin B complex?
A vitamin B complex is the collective name for all eight B vitamins that are essential for the healthy functioning of the body. The eight B vitamins that make up the vitamin B complex are:1,2,3
- vitamin B1 (thiamin)
- vitamin B2 (riboflavin)
- vitamin B3 (niacin)
- vitamin B5 (pantothenic acid)
- vitamin B6 (pyridoxine)
- vitamin B7 (biotin)
- vitamin B9 (folate)
- vitamin B12 (cobalamin)
The B vitamins are water-soluble, which means that their main properties are partly lost when food is washed or boiled.4 In addition, with the exception of biotin, B vitamins aren’t naturally produced by the body.1,3 This means that the main source of B vitamins is the food you eat.1
If you follow a vegan diet, you’re at a higher risk of a vitamin B12 deficiency.2,3 This is because vitamin B12 isn’t naturally found in foods like fruit, vegetables and grains – instead, it’s usually in meat, fish, eggs and dairy products.3 So, people who follow a vegan or plant-based diet may be advised to take a vitamin B12 supplement.5
What are the potential benefits of a vitamin B complex?
Each B vitamin is responsible for maintaining homeostasis.2,6 In short, this means they help keep all the processes in your body working properly to maintain your health and keep you alive.6 As well as this, each one plays a specific role in your body:1,2,3
- vitamin B1 – contributes to the normal function of your heart and nervous system and supports your body in breaking down and releasing energy from food
- vitamin B2 – contributes to the maintenance of normal red blood cells, mucous membranes, skin and vision. It also contributes to the reduction of tiredness and fatigue, protection of cells from oxidative stress, the normal functioning of the nervous system and supports your body in breaking down and releasing energy from food
- vitamin B3 – helps to keep your nervous system functioning normally and supports your body in breaking down and releasing energy from food
- vitamin B5 – contributes to the reduction of fatigue and normal mental performance as well as being involved in the normal synthesis and metabolism of steroid hormones, vitamin D and some neurotransmitters
- vitamin B6 – contributes to the normal function of the immune system, regulation of hormonal activity, the reduction of fatigue and the normal functioning of the brain and nervous system7,8
- vitamin B7 – helps your body metabolise fats, carbohydrates and protein, plus it helps maintain normal hair and skin9,10
- vitamin B9 – contributes to the normal function of the immune system and helps with normal blood formation, cell division and the growth of maternal tissue during pregnancy – which is often why it is found in many prenatal supplements. There’s evidence to suggest that supplementing folate during pregnancy could also reduce the risk of neural tube defects (a type of birth defect)11
- vitamin B12 – helps your body release energy from food, reduce fatigue, make red blood cells and keep the nervous and immune systems functioning normally12
Can B vitamins help with tiredness?
Feeling tired? It can be tempting to assume you’re missing a vitamin, but it’s not always that simple. Certain B vitamins, including B2, B3, B5, B6, folate and B12, contribute to the reduction of tiredness and fatigue.12 But that doesn’t mean taking a B-complex supplement will automatically leave you feeling more energised.
That’s because B vitamins don’t actually give you energy in the way calories from food do, and they don’t provide a quick pick-me-up like caffeine. Instead, several B vitamins contribute to normal energy-yielding metabolism, helping your body release and use energy from the food you eat.12,15 A healthy, balanced diet can help you get the vitamins and minerals your body needs. If your intake of a particular B vitamin is low, increasing it may help support normal function. But if you’re already getting enough, more doesn’t necessarily mean more energy.15
Fatigue and low energy can have lots of different causes, from poor sleep and stress to mental health, low physical activity, not eating enough, iron deficiency or an underlying medical condition. Nutrition can play a part, but it’s only one piece of the puzzle.15 If you’re experiencing persistent, unexplained or severe fatigue, speak to your GP rather than trying to diagnose the cause yourself. They can help work out what might be behind it and whether you need any further support.
Vitamin B12 and folate deficiencies can also cause megaloblastic anaemia, which affects the blood’s ability to carry oxygen around the body and can lead to tiredness, weakness and fatigue.16 Some people may be at greater risk of vitamin B12 deficiency, including those following a vegan diet, older adults, people with certain gastrointestinal conditions that affect nutrient absorption and those taking some medications.17
How much of each B vitamin do I need?
The amount of vitamin B you need depends on your age, sex and other factors, like whether you’re pregnant.1,3 As a result, the amount of each B vitamin that you need changes throughout your life.1 Below are the reference nutrient intakes for adults aged 19-64.3
| Vitamin | Female | Male |
|---|---|---|
| B1 | 0.8mg | 1mg |
| B2 | 1.1mg | 1.3mg |
| B3 | 13.2mg | 16.5mg |
| B5 | up to 200mg* | up to 200mg* |
| B6 | 1.2mg | 1.4mg |
| B7 | up to 0.9mg* | up to 0.9mg* |
| B9 | 200μg | 200μg |
| B12 | 1.5μg | 1.5μg |
*No reference nutrient intake. This is the amount that you shouldn't exceed in supplement form.
However, if you’re trying to conceive or are currently pregnant, you should take 400μg of folate (vitamin B9) until you’re 12 weeks pregnant.3
Sources of B vitamins in food
All the B vitamins you need are present in both plant and animal-based food products.2 As a result, eating a varied, balanced diet should ensure you get enough B vitamins day-to-day.3,10
Here are some excellent vitamin B food sources:3,9,12,13,14
- vitamin B1 – peas, fresh fruits (such as bananas and oranges), nuts, wholegrain breads, some fortified breakfast cereals, liver (but should be avoided if you’re pregnant)
- vitamin B2 – milk, eggs, fortified breakfast cereals, mushrooms, plain yoghurt
- vitamin B3 – meat, fish, wheat flour, eggs
- vitamin B5 – chicken, beef, liver (should be avoided if you’re pregnant), kidneys, eggs, mushrooms, avocado
- vitamin B6 – pork, poultry (such as chicken or turkey), some fish, peanuts, soya beans, wheatgerm, oats, bananas, milk, some fortified breakfast cereals
- vitamin B7 – organ meats, eggs, fish, seeds, soybeans, nuts
- vitamin B9 – broccoli, Brussels sprouts, leafy green vegetables (such as cabbage, kale, spring greens and spinach), peas, chickpeas and kidney beans, liver (should be avoided if you’re pregnant), breakfast cereals fortified with folic acid
- vitamin B12 – meat, fish, milk, cheese, eggs, some fortified breakfast cereals
What are the signs of low vitamin B?
Since each B vitamin plays a different role in the body, a deficiency in any one of the B complex vitamins can result in different symptoms. Below is a list of more specific symptoms associated with a deficiency in each B vitamin:10
- vitamin B1 and vitamin B2 – confusion and cracks along the side of the mouth
- vitamin B3 – digestive issues (nausea and abdominal cramps), mental confusion and a condition called pellagra, which causes diarrhoea
- vitamin B5 – personality changes, fatigue, headaches, irritability, nausea, stomach pains, muscle cramps, sleep disorders, upper respiratory infections, burning feet and an increased sensitivity to insulin
- vitamin B6 – anaemia, skin disorders (such as cracks and a rash around the mouth), confusion, depression, nausea, dermatitis and susceptibility to infections
- vitamin B7 – red rash (around the eyes, nose, mouth and genitals), hair loss, numbness and tingling in the hands and feet, lethargy, depression, hallucinations, seizures and impaired immune function
- vitamin B9 – fatigue, poor growth, diarrhoea, irritability, a tender or smooth tongue and neural tube defects in newborn babies
- vitamin B12 – mood changes, numbness or tingling (in hands, legs or feet), anaemia, loss of breath, pale skin, dizziness, difficulty walking, hallucinations, weight loss, poor memory, fatigue
As you can see, there are so many potential symptoms of low levels of B vitamins and many of these may be due to something else. So if you do experience any of the above symptoms, it’s important to check with your doctor first to rule anything else out.
B vitamin FAQS
It’s best to take supplements as stated on the packaging. Supplements like a vitamin B complex often take a few weeks or months to see full results, so stopping and starting B vitamins likely won’t offer the full benefits. If you do stop and start your supplements, be sure to get enough of the vitamins you’re missing through your diet instead.
According to the NHS, you only need to take a vitamin D supplement every day between October and March as these are the months where we don’t see as much sun. So, if you want to pause vitamin D in the summer and continue taking your usual supplements like vitamin B12, that’s no problem. However, if you have any specific reasons for changing your supplement routine, it’s best to talk to a registered nutritionist or healthcare professional for personalised guidance.
As with any supplements, you should always get approval from a medical professional before you start taking a B complex. You might not be suitable to take a B complex if you have certain health conditions.
The final say
So, it’s clear that this gang of eight vitamins is pretty vital. You should get all the B vitamins you need through a colourful and varied diet, but you might need a little extra help with some if you have dietary requirements or you’re vegetarian or vegan. If you’re on the hunt for a B complex, discover our top B vitamin supplements or our multivitamin round-up...
Disclaimer – This article provides informational advice and is not a substitute for medical care. Working with experts for accuracy, we take great care to ensure the information is up-to-date and relevant. However, you should always consult your GP or healthcare professional before using supplements or alternative products, particularly if you have medical conditions or are under supervision
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3. NHS. B vitamins and folic acid - Vitamins and minerals [Internet]. [cited 2024 Jul 18]. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
4. Hrubša M, et al. Biological properties of vitamins of the B-complex, part 1: Vitamins B1, B2, B3, and B5. Nutrients. 2022;14(3):484. https://doi.org/10.3390/nu14030484
5. NHS. The vegan diet [Internet]. [cited 2024 Jul 18]. Available from: https://www.nhs.uk/live-well/eat-well/how-to-eat-a-balanced-diet/the-vegan-diet/
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9. Hanna M, et al. B vitamins: Functions and uses in medicine. Perm J. 2022;26(2):89–97. https://doi.org/10.7812/tpp/21.204
10. LeBlanc JG. B-complex vitamins. IntechOpen; 2022. Available from: https://www.intechopen.com/books/11021
11. Moges N, Ermias Sisay Chanie, Rahel Mulatie Anteneh, Melkamu Aderajew Zemene, Asaye Alamneh Gebeyehu, Belete MA, et al. The effect of folic acid intake on congenital anomalies. A systematic review and meta-analysis. Frontiers in Pediatrics. 2024 Jul 19;12. https://pmc.ncbi.nlm.nih.gov/articles/PMC11294162/
12. European Commission. Food and Feed Information Portal Database: Health Claims [Internet]. [cited 2025 Feb 19]. Available from: https://ec.europa.eu/food/food-feed-portal/screen/health-claims/eu-register
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16. Castellanos-Sinco HB, Ramos-Peñafiel CO, Santoyo-Sánchez A, Collazo-Jaloma J, Martínez-Murillo C, Montaño-Figueroa E, et al. Megaloblastic anaemia: folic acid and vitamin B12 metabolism. Rev Med Hosp Gen Mex. 2015;78(3):135–43. Available from: https://www.sciencedirect.com/science/article/pii/S0185106315000426
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