Who is likely to be low in vitamin B12?

How common it is

In US national data from 2007 to 2018, about 3.6% of adults had a B12 deficiency (blood B12 below 200 pg/mL) and 12.5% had an insufficient level (below 300 pg/mL).^[1] Among older adults who live at home, 3% to 43% are deficient, depending on how deficiency is defined.^[1]

Groups at higher risk

• Older adults, especially those with atrophic gastritis, a condition of the stomach that lowers its acid and its intrinsic factor. It affects 2% of all people and 8% to 9% of adults aged 65 and over.^[1]
• People with autoimmune gastritis, also called pernicious anemia. The stomach makes no intrinsic factor, so the body cannot absorb B12 normally from food or supplements.^[1][2]
• People who had surgery on the stomach or the bowel, including many weight-loss operations.^[1][2]
• People with coeliac disease, and possibly people with Crohn's disease.^[1]
• Vegans and vegetarians, because B12 is found naturally only in animal foods. A 2024 review of 19 studies found lower B12 and higher homocysteine in vegans than in people who eat meat, and better levels in vegans who took B12 supplements.^[3][1]
• Babies who are breastfed by mothers who eat no animal foods.^[1]
• People who take metformin, proton pump inhibitors or H2 blockers for a long time.^[1] A 2016 meta-analysis found B12 levels 57 pmol/L lower after 6 weeks to 3 months of metformin.^[4] See Does metformin lower vitamin B12?
• People who use nitrous oxide (laughing gas) for recreation.^[2]

Signs of a low level

NICE lists these common signs:

• anemia or large red blood cells on a blood count^[2]
• tiredness without a clear cause^[2]
• pins and needles or numbness, balance problems and falls^[2]
• trouble concentrating or short-term memory loss^[2]
• a sore, swollen tongue (glossitis) and eyesight problems^[2]

Nerve signs can appear without anemia, so a normal blood count does not rule out a deficiency.^[1][2] The body stores 1 to 5 mg of B12, so signs can take several years to appear.^[1] A deficiency can also come with depression, anxiety or psychosis.^[2]

How it is tested

The first test measures total B12 or active B12 (holotranscobalamin) in the blood.^[2] NICE reads total B12 below 180 ng/L as a confirmed deficiency, 180 to 350 ng/L as a possible deficiency, and above 350 ng/L as an unlikely deficiency. When the result is unclear, a second test can measure methylmalonic acid (MMA).^[2] A B12 supplement can raise the result without fully treating a deficiency, so NICE advises taking the blood sample before treatment starts.^[2]