It's 3pm, your eyelids are heavy, and somebody tells you to "just take a B complex". It's one of the most common bits of supplement advice going. It's also one of the most misunderstood.
B vitamins do have an official, authorised link to tiredness. What that link covers, and what it doesn't, is where it gets interesting.
What the authorised claims actually say
B vitamins are the body's spark plugs. Thiamin (B1), riboflavin (B2), niacin (B3) and B12 all help release energy from the food you eat.[1] EFSA's riboflavin opinion looked at energy-yielding metabolism and at tiredness and fatigue,[2] and its B12 opinion concluded that B12 contributes to normal energy metabolism.[3] A separate B12 opinion assessed the tiredness and fatigue claim as well.[4]
On fatigue specifically, the UK's advertising regulator has noted EFSA's positive opinions for six B vitamins: riboflavin, niacin, pantothenic acid, B6, folate and B12.[5] The wording is "contributes to the reduction of tiredness and fatigue", and claims of this kind are listed on the Great Britain health claims register.[6]
Read that wording slowly. It says these nutrients contribute to normal function. It doesn't say a B complex will perk you up if your levels are already fine. That distinction gets lost in a lot of marketing.
What happens in trials when you're not deficient
Here the evidence cools. A 2021 meta-analysis in Nutrients pooled 16 randomised trials with 6,276 people who weren't overtly B12-deficient. B12 alone or as part of a B complex didn't improve cognition or depressive symptoms, and only one study looked at fatigue, so the authors couldn't draw a conclusion on it.[7]
The counter-argument comes from a 2016 review in the same journal, which argues that many people in developed countries fall short of recommended intakes for one or more B vitamins, and that optimal intake for each is still unclear.[8] It's a narrative review built largely on mechanisms, so treat it as a reason to look at your diet rather than proof that everyone needs a supplement.
"These nutrients contribute to normal function. That isn't the same as a lift for everyone."
When tiredness is a deficiency problem
Persistent, heavy tiredness is also the headline symptom of B12 or folate deficiency anaemia. The NHS says the most common cause in the UK is pernicious anaemia, where the immune system stops the body absorbing B12. Diet matters mainly for vegans, and some medicines, including proton pump inhibitors and anticonvulsants, reduce absorption. Around 1 in 10 people aged 75 or over are affected.[9]
That's a job for a blood test and your GP, not a guess at the supplement aisle. If you're plant-based, our piece on B12 absorption for vegans and vegetarians is a good place to start, and if you're a woman with heavy periods, iron is the other usual suspect.
Getting the dose right
B vitamins are water-soluble, so most are forgiving. B6 is the exception worth watching.
The NHS advises not taking more than 10mg of B6 a day in supplements unless a doctor says so, and notes that 200mg or more a day can lead to loss of feeling in the arms and legs. Effects between those figures aren't clear.[1] Niacin has its own limit too: high doses of nicotinic acid can cause flushing.[1]
So the useful test for any B complex is boring and practical: all eight B vitamins present, a B6 figure that respects that line, and a daily dose taken with food.
That's the bar the Ultra Vitamin B Complex is built around. One small tablet carries B1, B2, B3, B5, B6, B7, B9 and B12, it's suitable for vegetarians and vegans, and a 120-tablet bottle lasts four months. The per-tablet amounts are printed on the label, so check the B6 line against the 10mg figure above before you buy any B complex, ours included.
A fair way to think about it
If your diet is varied and your bloods are fine, a B complex is a safety net rather than a switch. If you're vegan, older, on long-term acid-reducing medication, or tired in a way that hasn't shifted for weeks, get tested first. Then you're supplementing for a reason, with a number to check against later.
Frequently asked questions
How long does a B complex take to work?
It depends on where you start. If a blood test has picked up a genuine B12 or folate shortfall, your GP will set the plan and the timeline. If your levels are already fine, the trial evidence we found doesn't show a reliable lift in energy, so don't expect to feel anything within a week or two.
Can you take a B complex every day?
Most people can, as long as the label amounts sit within normal limits. NHS guidance says supplements of 100mg or less of B1, 40mg or less of B2 and 2mg or less of B12 a day are unlikely to cause harm, while B6 should stay at 10mg a day or under unless a doctor advises otherwise. Read the per-tablet amounts before you buy anything.
Does vitamin B12 give you energy?
B12 contributes to normal energy-yielding metabolism, and a real deficiency causes extreme tiredness, so correcting one matters. For people who aren't deficient, a 2021 meta-analysis found too little fatigue data to draw conclusions. Our guide to B12 for vegans and vegetarians covers who is most likely to run low.
Is there a best time of day to take B vitamins?
We didn't find research showing that morning beats evening. Taking your tablet with food, as the Oxford Origins directions suggest, is the sensible part. Many people simply pick breakfast because it's easy to remember.
Sources
- NHS — B vitamins and folic acid: functions, sources and supplement limits (B6 10mg, 200mg nerve effects). https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
- EFSA — Scientific opinion on riboflavin health claims (energy-yielding metabolism; tiredness and fatigue). https://efsa.europa.eu/en/efsajournal/pub/1814
- EFSA — Opinion on vitamin B12 related claims (B12 contributes to normal energy metabolism). https://focalpointbg.com/images/stories/efsa/contents/pdfdocs/nda_op_ej1223_art13(1)_vitamin_B12_related_claims_en.pdf
- EFSA — Scientific opinion on vitamin B12 health claims (includes tiredness and fatigue claim). https://efsa.europa.eu/en/efsajournal/pub/1756
- ASA ruling on Natures Best Health Products Ltd — six B vitamins and reduced tiredness and fatigue. https://www.asa.org.uk/rulings/natures-best-health-products-ltd-a11-179089.html
- GOV.UK — Great Britain nutrition and health claims (NHC) register. https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register
- Burgstaller et al., Nutrients 2021 — Vitamin B12 supplementation, cognition, depressive symptoms and fatigue: systematic review and meta-analysis. https://www.mdpi.com/2072-6643/13/3/923/htm
- Kennedy, Nutrients 2016 — B Vitamins and the Brain: Mechanisms, Dose and Efficacy, a review. https://www.mdpi.com/2072-6643/8/2/68
- NHS — Vitamin B12 or folate deficiency anaemia: causes, symptoms and who is at risk. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/
At Oxford Origins, your wellbeing is our priority, and although we pride ourselves on our expertise in nutrition and supplementation, it's important to acknowledge the individuality of each person. Articles published by Oxford Origins are not intended to treat, diagnose, cure or prevent any disease, or replace the advice of your GP. We always recommend consulting with a healthcare provider if you encounter any health concerns, and we'll always be here to support you so you're never alone on your journey.
