AStrong evidence, for the people named belowVitamin
The short answer
Genuinely necessary for the groups listed and pointless for everyone else. If you eat meat, dairy and eggs regularly you almost certainly do not need it.
Who this is actually for
Vegans and strict vegetarians, people on long-term metformin or proton pump inhibitors, adults over about 65, and anyone with pernicious anaemia or after bowel surgery.
What it is legally allowed to claim
Quoted from the EU register of authorised health claims, Regulation (EU) 432/2012. A product may only make these claims if it supplies enough of the nutrient to qualify.
- Vitamin B12 contributes to normal energy-yielding metabolism
- Vitamin B12 contributes to normal red blood cell formation
How much is too much
No upper level established by EFSA. Excess is excreted.
Cautions and interactions
Never treat a suspected B12 deficiency by self-supplementing before testing. Folic acid can mask the blood picture while nerve damage continues.
Ask a pharmacist before you start anything. Interactions with prescribed medicines are the most common way supplements cause harm, and they are easy to check. Bring the actual packet, or a photo of the ingredients panel, because doses and forms vary enormously between products. Nothing here is a substitute for advice about your own situation.