Does vitamin B12 help memory?

What trials found

• A 2021 meta-analysis pooled 16 trials with 6,276 people who had no clear B12 deficiency and no advanced brain disease. Neither B12 alone nor B12 with folic acid and vitamin B6 improved any part of memory or thinking.^[1]
• A 2018 Cochrane review included 5 trials with 879 people with mild cognitive impairment, which means memory problems milder than dementia. B vitamins for 6 to 24 months probably had little or no effect on memory, planning, speed of thinking or quality of life.^[3]
• A Cochrane review included 14 trials with 27,882 healthy people, most of them aged 60 or over. Folic acid, B12 and vitamin B6 had little or no effect on overall thinking over up to 5 years.^[4]
• A trial gave 2,919 adults aged 65 and over 500 µg of B12 with 400 µg of folic acid a day for 2 years. Homocysteine fell, but test scores did not differ from placebo.^[4]
• A UK trial included 201 people aged 75 and over with a moderately low B12 level and no anemia. They took 1 mg (1,000 µg) of B12 a day or a placebo for 12 months. Blood B12 rose by 177%, but nerve function and thinking were no better than with placebo.^[5]

One review found a small effect

A 2022 meta-analysis of 25 trials found that B vitamins slowed the decline on the MMSE, a short test of memory and thinking, by 0.14 points. The effect was seen in trials that lasted more than 12 months and in people without dementia.^[6] In the same review, a higher intake of folate, but not of B12, was linked with a lower risk of dementia.^[6]

Why it might work

B12 helps turn homocysteine into methionine.^[4] In observational studies, high homocysteine is linked with Alzheimer's disease and dementia. Lowering it with B vitamins has not improved thinking in trials.^[4]

A deficiency is different

A real B12 deficiency can cause trouble concentrating and short-term memory loss, sometimes called brain fog. NICE lists these as signs that call for a B12 test when a person also has a risk factor, such as a vegan diet or metformin.^[2] Most of the trials above left out people with a clear deficiency.^[1][3] The UK trial is an exception: its people had a moderately low level but no anemia, and B12 still did not help their nerves or thinking.^[5] See Who is likely to be low in vitamin B12? and the goal cognition.

What is still unknown

One trial found slower brain shrinkage over 2 years with B vitamins, and better memory in people who had high homocysteine at the start. The Cochrane authors say other trials need to repeat this.^[3]