Vitamin B12 and B complex
Adults need about 1.5 micrograms of vitamin B12 a day, found almost only in animal foods.
Short answer Adults need about 1.5 micrograms of vitamin B12 a day, found almost only in animal foods. Vegans, and some older adults who absorb it less well, are the people most likely to need a supplement or fortified foods.
What B vitamins do
There are eight. Several, including B12, B6, niacin and riboflavin, contribute to normal energy-yielding metabolism and to the reduction of tiredness and fatigue. Folate and B12 contribute to normal blood formation.
B12 on its own or a B complex
| Choose | When |
|---|---|
| B12 alone | You eat no animal products, or a blood test showed low B12 |
| B complex | You want all eight at modest doses |
| A multivitamin | You want B vitamins with vitamin D and minerals |
A caution
Tiredness has many causes. If it persists, see a GP before reaching for a supplement: B12 deficiency needs diagnosing properly and is sometimes treated by injection. High doses of B6 over time can cause nerve problems.
Related pages
- Vitamins and mineralsMost people can get the vitamins and minerals they need from a varied diet.
- MultivitaminsA multivitamin is a safety net, not a shortcut.
- Iron supplementsWomen aged 19 to 49 need 14.8mg of iron a day and other adults 8.7mg.
Keep exploring
Questions people ask
Who needs vitamin B12 supplements?
Mainly vegans, and people diagnosed with low B12.
Does B12 give you energy?
It contributes to normal energy metabolism; it is not a stimulant.
Can I take this with medication?
Ask a pharmacist or GP first; some supplements interact with medicines.
Do supplements replace a balanced diet?
No. They are meant to add to a varied diet, not stand in for one.
Sources
- NHS: B vitamins and folic acid (opens in a new tab)
- Great Britain nutrition and health claims register (opens in a new tab)
Checked 9 October 2026.