This comprehensive booklet covers everything you need to know about B12 and ME/CFS, including what food groups are a good source of this vitamin, the benefits of B12, information regarding deficiency and possible treatments.
You can read the summary below or download the whole PDF leaflet.
What is vitamin B12?
- Vitamin B12 is a vitamin your body needs.
- It helps make energy.
- It helps repair your body.
- It helps your nerves work well.
- It helps make red blood cells.
Where does vitamin B12 come from?
Good foods with vitamin B12 are:
- Meat
- Salmon and other fish
- Milk
- Eggs
- Some breakfast cereals
- Yeast extract (like Marmite)
Fruit, grains, and vegetables do not have vitamin B12.
Your liver stores several years’ worth of B12. So a deficiency takes a long time to show up.
Signs of low vitamin B12
Some signs are the same as ME/CFS symptoms:
- Feeling very tired
- Weak or clumsy hands or feet
- Trouble with balance or walking
- Problems with eyesight
- Trouble with memory or concentration
- Pins and needles or numbness
- Headaches
- A fast or fluttering heartbeat
- Ringing noises in the ears (tinnitus)
Some signs are not usually part of ME/CFS:
- Feeling short of breath
- Low mood, anxiety, or (rarely) psychosis
- A sore red tongue
- Mouth ulcers
- Losing weight or appetite
- Skin looking pale yellow
- Eyesight slowly getting worse
If B12 is very low for a long time, it can badly damage the spinal cord and, in rare cases, cause heart failure. This is serious, so it needs to be checked.
What causes low vitamin B12?
- Pernicious anaemia – This is the most common cause in the UK. It’s an autoimmune illness. The immune system attacks the stomach, which stops B12 from being absorbed. It is more common in women around age 60.
- Poor diet – Not eating meat, dairy, or fish (for example, a vegan diet) without taking supplements.
- Some medicines – Including certain heartburn/indigestion drugs, metformin, and some others.
- Recreational nitrous oxide (laughing gas) – This can stop B12 working properly in the body.
- Gut problems – Such as Crohn’s disease, coeliac disease, or stomach surgery.
- Functional B12 deficiency – A rare problem where B12 can’t move properly between cells.
Is low B12 linked to ME/CFS?
- No. There is currently no good scientific evidence that vitamin B12 deficiency is part of what causes ME/CFS.
- But doctors should still rule out B12 deficiency when diagnosing ME/CFS — especially if there was no clear infection at the start, or if there are nerve-related symptoms.
Does taking vitamin B12 help ME/CFS?
- There is no strong evidence (from good clinical trials) that B12 supplements treat ME/CFS.
- The NHS guideline (NICE) does not recommend vitamin supplements for ME/CFS.
- Some people with ME/CFS say B12 helps them. Some doctors agree.
- One small Swedish study followed 38 people with ME/CFS who had B12 injections plus folic acid every week for 6 months:
- 15 people felt a lot better
- 23 people felt a little better
- The ME Association is looking into funding a proper clinical trial on this.
Important safety point
! Before taking any B12 supplement, make sure pernicious anaemia has been ruled out by your doctor.
- If you already have pernicious anaemia, tablets or supplements won’t work — you need B12 by injection.
- Taking B12 supplements before being tested can affect the results of a blood test. Talk to your doctor about stopping supplements before testing.
- Untreated pernicious anaemia can cause permanent nerve and spinal cord damage.
How is low B12 diagnosed?
- A blood test checks total B12 and active B12.
- Doctors may also check folate levels, as low folate causes similar symptoms.
- Extra tests (like intrinsic factor antibody tests) can help confirm pernicious anaemia.
How is low B12 treated?
| Cause | Treatment |
| Poor diet | B12 tablets + eating more B12-rich foods |
| Pernicious anaemia or poor absorption | B12 injections (for life, every 3 months after the first course) |
Vitamin B12 injections are generally safe. Minor side effects can include:
- Fever
- Headache
- Nausea
- Dizziness
Key takeaways
- Low B12 causes tiredness and other symptoms similar to ME/CFS — so it should be checked for.
- There’s no proof low B12 is a cause of ME/CFS itself.
- There’s no strong proof B12 supplements treat ME/CFS.
- Always rule out pernicious anaemia before self-treating with B12.
- People on vegan or very restricted diets should take B12 supplements or fortified foods.
Want to know more?
- NICE Guideline on Vitamin B12: nice.org.uk/guidance/ng239
- Pernicious Anaemia Society: https://pernicious-anaemia-society.org/
- ME Connect support line: 0808 801 0484 (Freephone) or email: meconnect@meassociation.org.uk
This is a simplified summary for information only. It is not medical advice. Please talk to your doctor about your own symptoms and treatment.