What is vitamin B12 used for?

Low B12 levels

The best evidence is for treating and preventing a low B12 level. A 2018 Cochrane review of 3 trials with 153 people found that tablets of 1,000 to 2,000 µg a day brought low blood levels back to normal about as well as injections. The quality of the evidence was low.^[1] A 2024 review of 13 studies with 4,275 patients found no significant difference between tablets, tablets under the tongue and injections.^[5] This use belongs to the goal essential health. The protocol for a low B12 level lists the doses that trials used.

Nerve damage in diabetes

Methylcobalamin, one form of B12, is used for nerve damage (neuropathy). A 2020 review pooled 15 trials with 1,707 people with nerve damage from diabetes or shingles. More people reached a set level of overall improvement with methylcobalamin alone than with other treatments (risk ratio 1.17), but pain and symptom scores did not improve. Most of the trials had a high risk of bias, and the authors called the evidence for methylcobalamin alone unclear.^[2] In a 1-year trial, 90 people with type 2 diabetes and nerve damage who took metformin and had B12 below 400 pmol/L got 1,000 µg of methylcobalamin a day or a placebo. Nerve tests, pain and quality of life improved in the B12 group, and several nerve tests and pain got worse in the placebo group.^[6] This belongs to the goal organ function.

Heart and blood vessels

B12, folic acid and vitamin B6 lower homocysteine, an amino acid that is linked with heart disease.^[7] A 2017 Cochrane review of 15 trials with 71,422 people found that these vitamins did not prevent heart attacks or deaths. Strokes were slightly fewer: 4.3% in the vitamin groups against 5.1% in the placebo groups.^[3] See the goal cardiovascular.

Memory, mood and energy

A 2021 review of 16 trials with 6,276 people who had no clear deficiency found no effect of B12 on memory, thinking or depression.^[4] NIH ODS states that B12 does not appear to improve athletic performance or endurance in people who have enough of it.^[7] See the goals cognition and energy.

Pregnancy

A 2024 Cochrane review of 5 trials with 984 pregnant women found that B12 supplements may lower the share of mothers with a deficiency: 25.9% against 67.9%. The evidence was very uncertain, and the review could not show effects on anemia, preterm birth or the child's development.^[8]

Who takes it

In US national data from 2017 to 2020, about 24% of men and 29% of women took a supplement that contained B12.^[7] The groups most likely to be low in B12 include older adults, vegans and vegetarians, and people who take metformin or stomach acid medicines. See Who is likely to be low in vitamin B12?^[7]