What is vitamin B12, and who needs a supplement?
Last updated: June 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Vitamin B12's role in nerves and blood, who's at risk of deficiency, and why it only 'boosts energy' if you're low.
Key takeaways
- B12 is essential for nerves and blood; deficiency can cause fatigue and lasting nerve damage.
- At-risk groups: vegans, older adults, and people on metformin or acid-reducers.
- It boosts energy only if you're deficient — extra B12 does little when levels are normal.
What vitamin B12 does
Vitamin B12 is essential for making red blood cells, maintaining the nervous system, and DNA production. The body can store it for a while, but a sustained shortfall causes real problems. It's found almost entirely in animal foods, which is the root of many deficiencies. B12 is also one of the most aggressively marketed 'energy' vitamins — a claim that's true in one specific situation and misleading in another.
Who is at risk of deficiency
Certain groups are genuinely prone to B12 deficiency. Vegans and strict vegetarians, because B12 comes from animal foods. Older adults, who often absorb it less well. People on long-term metformin or acid-reducing medication (PPIs), which can impair absorption. And those with pernicious anaemia or gut conditions affecting absorption. For these groups, a B12 supplement addresses a real, sometimes serious, gap.
What deficiency looks like
B12 deficiency can cause fatigue, a particular type of anaemia, and — importantly — neurological symptoms like tingling or numbness in the hands and feet, balance problems, and cognitive or mood changes. Some nerve damage can become permanent if a deficiency is prolonged, which is why it shouldn't be ignored. A blood test is the way to confirm it rather than guessing from symptoms alone.
The 'energy boost' myth
B12 is sold heavily as an energy booster, and here's the honest version: correcting a genuine B12 deficiency can dramatically improve energy, because the deficiency was causing fatigue. But taking extra B12 when your levels are already normal does not give you an energy boost — your body simply excretes the excess. So B12 'for energy' helps if you're deficient and does little if you're not.
Forms, doses and absorption
B12 supplements come as cyanocobalamin or methylcobalamin; both work for most people. Because absorption can be the problem, people with absorption issues sometimes need higher oral doses or injections, guided by a doctor. For at-risk groups like vegans, a regular oral supplement is usually enough. As a water-soluble vitamin, B12 has low toxicity, but that's not a reason to take large doses without need.
The verdict
Vitamin B12 is genuinely important and worth supplementing if you're in an at-risk group or have a confirmed deficiency — where it can make a real difference, including for nerve symptoms. But as a routine 'energy boost' for people who aren't deficient, it does little. A blood test beats guessing, and unexplained fatigue or nerve symptoms deserve a proper check rather than a self-prescribed B12 habit.
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Frequently asked questions
Who needs a vitamin B12 supplement?
Vegans, older adults, and people on metformin or acid-reducing medication, plus anyone with a confirmed deficiency.
Does B12 give you energy?
Only if you're deficient — correcting a shortfall can improve energy, but extra B12 does little when levels are already normal.
What are signs of B12 deficiency?
Fatigue, a type of anaemia, and nerve symptoms like tingling, numbness or balance problems — confirmed by a blood test.
Which form of B12 is best?
Cyanocobalamin and methylcobalamin both work for most people; absorption issues may need higher doses or injections.
This article is general information, not medical advice. See our medical disclaimer, and talk to a qualified healthcare professional about your own situation.