B-complex

What it is

B-complex supplements combine the eight B vitamins: B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate) and B12 (cobalamin). They are found in meat, fish, eggs, dairy, wholegrains, legumes and fortified cereals.

People take them for energy, stress, mood and skin or hair. The B vitamins do play roles in turning food into energy, but that does not mean extra gives you more of it.

They are water-soluble, so what you do not use is mostly passed out in urine, which turns bright yellow because of riboflavin.

How it works

B vitamins work as helpers (coenzymes) in the reactions that release energy from food, make DNA and red blood cells, and keep nerves working. Deficiency in any of them can cause fatigue and nerve problems.

What the evidence says

• Strong Correcting deficiency in poor diets or absorption problems
  Works if you are actually low in one or more B vitamins.
• Weak Reducing fatigue in people who are not deficient
  Little evidence that extra Bs give extra energy to well-nourished people.
• Limited Stress and mood
  Some small trials show modest improvement in self-reported stress, mostly with multivitamin-style blends and short follow-up.
• Moderate Supporting people on metformin, acid reducers or heavy drinking
  These can reduce absorption of B12, folate or thiamin, so supplementation can make sense.
• Weak Skin, hair and nails
  Mostly applies to biotin deficiency, which is rare.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Daily needs for each B vitamin are small (a few micrograms to a few milligrams); check the NHS reference intakes.
• B-complex products often exceed needs several times over. Pick one with lower, nutritionally relevant amounts if you can.
• Take with breakfast; B vitamins can be mildly stimulating for some and may disturb sleep if taken late.
• Watch B6 and B3 (niacin) doses specifically: see risks.

Forms and what to look for

• Standard forms (cyanocobalamin, folic acid, pyridoxine hydrochloride) are cheap and effective for most.
• Active forms (methylcobalamin, methylfolate, pyridoxal-5-phosphate) are marketed for people with gene variants like MTHFR; evidence that they are better for the general public is limited.
• Niacin can cause flushing, while niacinamide does not.
• Gummies and powders vary widely in actual content.

What to expect, and when

• If deficient, fatigue and mood may improve over several weeks.
• Neurological recovery from deficiency can take months.
• Otherwise expect no difference, apart from brighter urine.

Side effects

• Bright yellow urine is harmless.
• Nausea or stomach upset, especially on an empty stomach.
• Niacin can cause flushing and itching.
• High B6 over time can cause nerve symptoms such as tingling.
• Acne-like skin breakouts have been reported with high B12 or B6.

Interactions

• B6 can reduce the effect of levodopa (a Parkinson medicine) unless it is combined with carbidopa.
• Folic acid can interact with methotrexate and some anti-seizure drugs such as phenytoin.
• Niacin at high doses can affect statins, blood sugar and blood pressure medicines.
• Folic acid alone can mask B12 deficiency.

Who should avoid it

• Anyone on methotrexate, phenytoin, levodopa or similar medicines without checking first.
• People with liver disease, gout or peptic ulcers should be cautious with high-dose niacin.
• Pregnant women should use a pregnancy-specific product and follow NHS advice.
• Anyone who develops tingling or numbness should stop and check with a clinician.

Risks and safety

• Long-term B6 above about 10 mg a day (UK advisory level for supplements) has been linked to nerve damage; many B-complex products exceed this, so check current guidance.
• High-dose niacin can harm the liver.
• Not banned in sport.
• Combined "energy" shots with high Bs and caffeine can cause jitteriness.

Buying well: quality and testing

• Check the dose of B6 first, then niacin and folic acid.
• Third-party seals (NSF, USP, Informed Sport) add confidence.
• Prefer products that list each B vitamin with amounts, not a proprietary blend.
• Higher numbers do not mean better value.

Bottom line

A B-complex is a decent insurance policy for people with limited diets, older adults or those on certain medicines. For everyone else it mostly gives you expensive yellow urine. If you take one, choose a moderate dose, especially of B6.