Vitamin B Complex: Benefits, Deficiency Signs and When to Supplement

Vitamin B complex is a group of eight water-soluble vitamins that work together to help your body turn food into energy, keep your nervous system running, and support the healthy formation of red blood cells. Because these vitamins are not stored in the body for long, a limited diet, certain health conditions, or particular life stages can leave you short of one or more of them without it being obvious straight away. This guide covers what vitamin B complex actually does, the deficiency signs worth knowing, and how to work out whether a supplement is worth adding to your routine.

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• What is vitamin B complex?
• What does vitamin B complex do in the body?
• What are the signs of a vitamin B deficiency?
• Who is more likely to be low in B vitamins?
• What foods are rich in B vitamins?
• When should you consider a B complex supplement?
• Vitamin B complex vs vitamin B12: what's the difference?
• Are there any side effects to be aware of?
• Frequently Asked Questions

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What is vitamin B complex?

"Vitamin B complex" is a collective term for eight distinct B vitamins that are usually grouped together because their roles in the body overlap so closely. These are vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), vitamin B7 (biotin), vitamin B9 (folate) and vitamin B12 (cobalamin).

All eight are water-soluble, which means your body cannot store large reserves of most of them the way it can with fat-soluble vitamins like A, D, E and K. Any excess is generally passed out in urine within a day or two, so a regular supply from food, or occasionally a supplement, matters more than it does for other nutrients.¹ Vitamin B12 is the exception. The body can store several years' worth in the liver, which is why a deficiency can take a long time to become noticeable.⁴

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What does vitamin B complex do in the body?

Taken together, B vitamins contribute to several everyday body functions rather than one single job. Several of them, including B1, B2, B3, B6, B7 and B12, contribute to normal energy-yielding metabolism, which is one reason low intake is often associated with feeling run down.⁶ The same group, alongside B12 specifically, also supports the normal function of the nervous system.

B6, folate (B9) and B12 additionally contribute to normal red blood cell formation and normal homocysteine metabolism, while B6, B12 and biotin contribute to normal psychological function.⁶ Biotin also supports the maintenance of normal hair and skin.⁶

Folate has a particularly important role during pregnancy. Maternal folate intake contributes to the normal development of the baby's neural tube, which is why women who are pregnant or could become pregnant are generally advised to take a folic acid supplement. This should always be discussed with a GP or midwife first, since the recommended dose can vary depending on individual risk factors.¹

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What are the signs of a vitamin B deficiency?

The exact signs depend on which B vitamin is running low, but vitamin B12 and folate deficiencies are the most common in the UK and tend to overlap in how they present. Typical signs include:

• Persistent tiredness or low energy, even after adequate rest
• Pale or slightly yellowish skin
• Tingling or numbness in the hands and feet
• A sore, red tongue or mouth ulcers
• Low mood, irritability or difficulty concentrating
• In more advanced cases, problems with balance, memory or vision³

This is a more common issue than many people assume. Recent analysis of UK national dietary survey data found that over 70% of women of reproductive age had folate levels below the threshold recommended for protection against neural tube defects in pregnancy, rising to over 85% among women aged 21 to 25.⁷ Older adults are also frequently affected by low vitamin B12 status, largely due to reduced absorption rather than diet alone.⁴

If you recognise several of these signs, it's worth speaking to a GP, who can arrange a blood test to check vitamin B12 and folate levels. These conditions are usually fairly straightforward to diagnose and treat, but it's important not to self-diagnose or self-treat, as some of the neurological effects of a prolonged deficiency can become difficult to reverse if left untreated.²

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Who is more likely to be low in B vitamins?

Some groups are at meaningfully higher risk of running low on one or more B vitamins:

• People following a vegan or largely plant-based diet: vitamin B12 occurs naturally only in animal-derived foods, so anyone not eating meat, fish, eggs or dairy needs a reliable alternative source.¹
• Older adults: stomach acid production naturally declines with age, which reduces the body's ability to absorb vitamin B12 from food.⁴
• People taking certain medicines: long-term use of metformin or proton pump inhibitors (PPIs) for acid reflux can reduce vitamin B12 absorption over time.¹
• People who are pregnant or breastfeeding: folate requirements increase significantly during pregnancy.¹
• People with digestive conditions: coeliac disease, Crohn's disease and pernicious anaemia can all interfere with how well B vitamins are absorbed.⁵
• People with a generally restrictive diet or high alcohol intake: both can reduce overall intake of several B vitamins at once.¹

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What foods are rich in B vitamins?

Most people can meet their B vitamin needs through a varied, balanced diet. Wholegrains, meat, fish and eggs are good all-round sources of several B vitamins, while dairy products contribute meaningfully to B12 and riboflavin intake. Leafy green vegetables, peas, chickpeas and brown rice are among the best sources of folate, and fortified breakfast cereals can be a useful top-up for both folate and B12, particularly for anyone eating a largely plant-based diet.^1,8

Because vitamin B12 is found almost exclusively in animal products, this is the one B vitamin where diet alone is genuinely difficult for vegans to manage without fortified foods or a supplement.¹

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When should you consider a B complex supplement?

Most healthy adults eating a varied, balanced diet don't need to take extra B vitamins on top of what they get from food.¹ A supplement tends to make more sense if you fall into one of the higher-risk groups above, if your diet is genuinely limited for any reason, or if a GP has confirmed a deficiency through a blood test and recommended supplementation as part of your treatment plan.

If you decide a B complex is right for you, timing is mostly about personal preference rather than clinical necessity. Because B vitamins are involved in energy metabolism, many people find it more natural to take a B complex supplement in the morning or with breakfast rather than later in the day.

OneVit B Complex provides all eight B vitamins in a single daily capsule, which makes it a straightforward option if you want broad coverage across the whole group rather than targeting one vitamin in isolation.

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Vitamin B complex vs vitamin B12: what's the difference?

A vitamin B complex already contains vitamin B12 as one of its eight vitamins, so it's not a case of choosing one over the other in every situation - it depends on what you are trying to address. A standalone B12 supplement, such as OneVit Vitamin B12, delivers a single, more concentrated dose of just that one vitamin. This tends to suit people with a specific, known need for extra B12, such as vegans or those with absorption difficulties, more precisely than a broader B complex would.

A B complex, by contrast, is a better fit if you want general coverage across all eight B vitamins rather than one in particular. If your goal is even broader nutritional coverage that includes B vitamins alongside other vitamins and minerals, OneVit Complete Multivitamin is worth considering instead, since it includes B vitamins as part of a wider daily formulation.

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Are there any side effects to be aware of?

Because B vitamins are water-soluble, your body generally excretes what it does not need, which makes serious harm from food sources very unlikely. One harmless and fairly common effect of taking a B complex supplement is bright yellow urine, caused by riboflavin (vitamin B2), and this is not a cause for concern.¹

Vitamin B6 is the main exception. Taking more than 200mg a day over a long period can cause a loss of feeling in the arms and legs, known as peripheral neuropathy, and this may not fully resolve once you stop taking the supplement.¹ This level of intake is far higher than what is found in a standard B complex supplement, but it's a reminder not to exceed the amount stated on the label. If you are pregnant, breastfeeding, taking prescribed medication, or living with an existing health condition, speak to a GP or pharmacist before starting a vitamin B complex supplement.

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Frequently Asked Questions

How long does it take for a vitamin B complex to work? This varies depending on why you are taking it. If you are simply topping up a generally adequate diet, you may not notice a distinct change at all. If a GP has identified a genuine deficiency, it can take several weeks to a few months of consistent supplementation, alongside any treatment they recommend, before levels and symptoms improve.

Can I take vitamin B complex every day? Yes, a daily B complex supplement taken at the dose stated on the label is generally considered safe for most healthy adults, since excess B vitamins are water-soluble and are not stored in large amounts.¹

Does vitamin B complex give you energy? Several B vitamins contribute to normal energy-yielding metabolism, which is the process your body uses to convert food into usable energy.⁶ This is different from a stimulant effect, so it will not give you an immediate energy spike the way caffeine might.

What is the difference between vitamin B complex and folic acid? Folic acid is the supplement form of folate, which is one of the eight B vitamins (vitamin B9) included within a vitamin B complex. Taking a B complex means you are getting folate alongside the other seven B vitamins, rather than folate on its own.

Can you take vitamin B complex alongside other supplements? In general, yes. B vitamins do not typically interact with common supplements like vitamin D or omega-3. If you are taking multiple supplements, it's worth checking you are not significantly exceeding the recommended amount of any single vitamin across products.

Who should be cautious with vitamin B complex? Anyone taking prescribed medication, particularly for acid reflux, diabetes, or a condition affecting the nervous system, should speak to a GP or pharmacist before starting a B complex, since some medicines can affect how B vitamins are absorbed or processed.¹

Is it better to get B vitamins from food or from a supplement? Food is generally the preferred source for most people, since a varied diet provides B vitamins alongside other nutrients your body needs.¹ A supplement is best thought of as a way to fill genuine gaps, rather than a replacement for a balanced diet.

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References

1. NHS. Vitamins and minerals – B vitamins and folic acid. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
2. NHS. Vitamin B12 or folate deficiency anaemia. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/
3. NHS. Vitamin B12 or folate deficiency anaemia – Symptoms. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/symptoms/
4. NHS. Vitamin B12 or folate deficiency anaemia – Causes. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/causes/
5. NHS. Vitamin B12 or folate deficiency anaemia – Treatment. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/treatment/
6. GOV.UK. Great Britain Nutrition and Health Claims (NHC) Register. https://www.gov.uk/guidance/great-britain-nutrition-and-health-claims-nhc-register
7. Folate status and its relationship with vitamin B12 in the UK population. European Journal of Nutrition. 2025. https://link.springer.com/article/10.1007/s00394-025-03796-6
8. British Dietetic Association. Folic Acid Food Fact Sheet. https://www.uhsussex.nhs.uk/wp-content/uploads/2023/03/folicacidbda.pdf

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This article is for informational purposes only and does not constitute medical advice. If you are concerned about a possible vitamin B deficiency, consult a GP or qualified healthcare professional.