Vitamin B12, honestly — who actually needs it

B12 is a supplement most people don’t need — and a few genuinely must have. The honest headline: if you eat animal foods and absorb normally, you’re likely fine; but vegans, many older adults and long-term metformin users are at real risk, and untreated deficiency can cause permanent nerve damage.

A vitamin with a real deficiency story

Vitamin B12 is essential for making red blood cells and keeping nerves healthy, and it comes almost entirely from animal foods. Unlike most "everyone should supplement" hype, B12 is the opposite: broadly unnecessary for those who eat meat, fish, eggs or dairy and absorb it well — but genuinely important for specific groups.

What makes it matter: deficiency can develop silently and, left too long, cause nerve and cognitive damage that may not fully reverse.

Who is genuinely at risk

Know if you’re in one of these groups.

• Vegans and strict vegetarians — B12 is essentially absent from plant foods, so a reliable supplement or fortified foods are non-negotiable on a vegan diet. This is not optional. (established)
• Many older adults — With age, reduced stomach acid impairs absorption of B12 from food, so deficiency becomes common later in life even in meat-eaters. (established)
• Long-term metformin users (and acid-reducer users) — Metformin can reduce B12 absorption over time, and so can long-term acid-suppressing drugs. Worth periodic checking if you take them. (established)

The honest bottom line

• Test if at risk; supplement if low — If you’re in a risk group or have symptoms (fatigue, tingling, memory issues), get a blood test rather than guessing. Correcting a real deficiency is cheap and effective; supplementing when you’re already replete does nothing. (note)
• Most others don’t need it — For a mixed-diet adult who absorbs normally, routine B12 supplements add no benefit — the "energy boost" from B12 only appears if you were actually deficient. (note)

What we still don’t know

• The exact metformin risk figure Estimates of B12 deficiency in long-term metformin users vary widely across studies; the risk is real but the precise rate isn’t pinned down.
• Ideal screening intervals How often at-risk groups should be tested isn’t firmly standardised.

Key terms

• Vitamin B12 A nutrient (from animal foods) essential for red blood cells and nerves; deficiency can cause anaemia and nerve damage.
• Deficiency Too little of a nutrient to function normally; B12 deficiency can develop silently.
• Megaloblastic anaemia A type of anaemia caused by B12 (or folate) deficiency, producing large, ineffective red blood cells.
• Metformin A common diabetes drug that can reduce B12 absorption with long-term use.