Vitamin B12 Deficiency and Tiredness

What B12 does and why low levels matter

Vitamin B12 and folate help keep the nervous system healthy, among other functions. When the body lacks enough B12 or folate it can make abnormally large red blood cells that cannot work properly, which is called vitamin B12 or folate deficiency anemia. [1] Deficiency can also occur without anemia. [1]

Symptoms that can occur

NHS lists extreme tiredness, a lack of energy, pins and needles, a sore red tongue, mouth ulcers, muscle weakness, vision problems, and psychological symptoms from mild depression or anxiety to confusion, plus problems with memory and judgement. [1] Because these overlap with many conditions, they cannot show deficiency on their own. See Why am I so tired?.

Why getting checked promptly matters

NHS says it is important for B12 or folate deficiency to be diagnosed and treated early, because although many symptoms improve with treatment, some problems caused by the condition can be irreversible. [1] Complications can include nervous system problems that sometimes become permanent. [1]

Who is more likely to be low

• Pernicious anemia, where the immune system attacks cells in the stomach so B12 from food is not absorbed, is the most common cause of B12 deficiency in the UK. [1]
• Diet: a vegan diet without B12 supplements or fortified foods, a restrictive diet, or a poor diet for a long time. [1]
• Medicines: certain medicines, including anticonvulsants and proton pump inhibitors, can affect absorption. [1]
• Age: NHS reports deficiency in around 1 in 10 people aged 75 or over and 1 in 20 aged 65 to 74. [1]
• Absorption conditions: MedlinePlus lists diseases causing malabsorption, such as celiac disease and Crohn disease. [2]

Testing

A B12 blood level is the usual test. MedlinePlus says a low value is a possible sign of deficiency and that it should be confirmed by checking methylmalonic acid, where a high level points to true B12 deficiency. Some medicines, such as metformin and proton pump inhibitors, can affect test results, and you should not stop medicines before talking to your provider. [2]

Established care

Most cases are treated with B12 injections or tablets. Injections are usually given first, and treatment may last until levels improve or for life. [1] Dietary B12 comes from meat, fish, eggs, dairy products and fortified foods. [1] See Fortified foods and Oily fish.

Do B12 supplements boost energy in people who are not deficient?

Evidence: insufficient. A 2021 systematic review of 16 randomized trials (6,276 people) looked at B12 or B complex in people without overt deficiency or advanced neurological disorders. It found no effect on cognitive function or depression, and only one study reported idiopathic (unexplained) fatigue, so the review could not analyze fatigue. [3] For ME/CFS, NHS says there is insufficient evidence to recommend supplements such as vitamin B12. [4] In a small randomized crossover trial of 32 healthy adults, a 28-day B-vitamin complex was reported to lengthen running time to exhaustion, but it was one small study of a single product. [5]

Safety

Do not guess at deficiency. Symptoms such as numbness, tingling, balance trouble or confusion need assessment rather than self-treatment. [2] [1] If you take other medicines or supplements, see How interactions work and Fatigue: when to get help. Compare other products on Energy supplements compared.

When to get help

See a GP or clinician if you think you may have a vitamin B12 or folate deficiency. [1]