Vitamin B complex: functions, foods, deficiency and supplements

Find out all about vitamin B, including what it does, how much you need, where to find it, and who might need to supplement their diet.

Overview of vitamin B

What is vitamin B complex and what does it do?

Vitamin B is the name for a group of eight B vitamins that are essential for the healthy functioning of the body, while vitamin B complex is a supplement containing all the B vitamins you need each day.¹

Vitamin B complex usually contains these nutrients:²

thiamin (vitamin B1)
riboflavin (vitamin B2)
niacin (vitamin B3)
pantothenic acid (vitamin B5)
pyridoxine (vitamin B6)
biotin (vitamin B7)
folic acid (vitamin B9) – this is the synthetic version of folate
cyanocobalamin (vitamin B12)

Each B vitamin has a different function and is needed in different amounts. In general, B vitamins help to release energy from food while keeping your blood, skin and nervous system healthy.³ The B vitamins are water soluble, which means that – with the exception of vitamin B12 – they can’t be stored in the body, so you need to replace them every day.⁴ Most people get all the B vits they need from their diet, with good sources including seeds, fish, eggs, meat, poultry, and leafy greens.⁵ If you’re vegan, you could be at risk of B12 deficiency because this nutrient is only found in animal sources such as meat, fish and dairy. Symptoms include muscle weakness and extreme tiredness.⁶

Functions of vitamin B

What do the B vitamins do in the body?

thiamin – helps turn carbohydrates and sugar into energy, plays a key role in nerve, muscle and heart function, and is essential for a healthy brain

riboflavin – important for energy release, helps the body to absorb nutrients, including iron, and is crucial for healthy eyes, skin and nervous system⁸

niacin – helps release energy from food, keeps the nervous and digestive systems healthy, and is essential for normal growth and healthy skin⁹

pantothenic acid – helps the body turn protein and fat into energy, and is needed for healthy growth¹⁰

pyridoxine – helps break down protein from food, reduces tiredness and fatigue, and is essential for healthy red blood cells and nervous system¹¹

biotin – helps the body break down nutrients from food and process glucose, maintain mucous membranes, and keeps skin and nails healthy¹²

folate/folic acid – essential during pregnancy to help prevent neural tube defects (spina bifida) in babies, helps maintain healthy red blood cells, and contributes to reduction of fatigue¹³

vitamin B12 – vital for the nervous and immune systems, helps fight tiredness and fatigue, and needed for healthy DNA¹⁴

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. Below are the reference nutrient intakes (RNIs) for women and men:¹⁵

thiamin (B1) – women 0.8mg, men 1mg
riboflavin (B2) – women 1.1g, men 1.3mg
niacin (B3) – women 13.2mg, men 16.5mg
pantothenic acid (B5) – women and men up to 200mg
pyridoxine (B6) – women 1.2mg, men 1.5mg
biotin (B7) – up to 0.9mg a day for both women and men
folate (B9) – women and men 200mcg. However, women who are trying to conceive or pregnant should take 400mcg until 12 weeks pregnant
vitamin B12 – women and men 1.5mcg

Vitamin B foods

Which foods are the best sources of vitamin B?

It’s easy to eat a diet packed with B vitamins. Here’s where to find your eight essential B vitamins:

thiamin – wholemeal bread, peas, eggs, beans, brown rice¹⁶

riboflavin – milk, eggs, fortified breakfast cereals, cheese, certain green veg¹⁷

niacin – bread, potatoes, peas, peanuts, brown rice, salmon¹⁸

pantothenic acid – wholegrains, eggs, green leafy veg, avocado, potatoes¹⁹

pyridoxine – wholegrains, eggs, soya beans, fish, vegetables, peanuts, milk, potatoes²⁰

biotin – egg yolk, legumes, yeast, nuts, milk²¹

folate – Brussels sprouts, dark green leafy vegetables, peas, chickpeas, fortified breakfast cereals²²

vitamin B12 – milk, cheese, eggs, salmon, meat, fortified breakfast cereals, plant milks²³

Vitamin B deficiency

What are the symptoms of a vitamin B deficiency?

Vitamin B deficiency is rare in the UK, but two of the more common ones are a lack of vitamin B12 and folate.

Older people and vegans are most at risk of low vitamin B12 levels: older people because they produce too little ‘intrinsic factor’ in the stomach – a natural chemical that boosts B12 absorption – and vegans because they eat mainly plant foods.

Folic acid insufficiency now affects 75% of women of childbearing age in the UK, which could have a negative impact on foetal health.

A vitamin B12 or folate deficiency can lead to a type of anaemia called megaloblastic anaemia, where you produce red blood cells that are larger than normal. Symptoms include fatigue, feeling short of breath, racing heart, diarrhoea and nausea.^24,25

What happens if I consume too much vitamin B?

As B vitamins are water soluble, it’s tricky to get too much from your diet or from taking a vitamin B complex.²⁶However, taking large amounts of single B nutrients as supplements may cause side effects such as vomiting, liver damage or nerve damage.^27,28,29 Shop Vitamins Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.Written by Carole Beck on October 24, 2018 Reviewed by Dr Carrie Ruxton PhD on November 3, 2018

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