Vitamin B12 and neuropathy: symptoms, testing and treatment

If your feet tingle or feel numb, someone has probably suggested that you might be low on vitamin B12. It is a reasonable idea. B12 is one of the known, and treatable, causes of nerve damage. But it is not the cause for everyone, and taking supplements without knowing your level can leave the real answer unexplored. Here is what the evidence says.

Why B12 matters for nerves

Vitamin B12 deficiency can cause a wide range of symptoms, and those symptoms may be irreversible if it isn’t diagnosed and treated in a timely manner. An expert consensus panel of 42 doctors agreed that recognizing symptoms should have the highest priority when making the diagnosis.^[3] In the feet, that usually looks like a peripheral neuropathy: numbness, tingling or burning in the toes and feet, typically on both sides, often creeping upward over time.^[2]

Other symptoms named in a clinical review include fatigue, “brain fog,” depression and ataxia, which means unsteadiness when walking.^[1]

Who is at risk

According to a 2025 review, risk factors include:^[1]

• conditions that interfere with absorption from the gut
• limited dietary intake of B12
• medicines such as metformin and proton pump inhibitors
• older age

Metformin deserves a special mention because so many people with diabetes take it. In a long-term follow-up of the Diabetes Prevention Program, low B12 was more common in the metformin group than in the placebo group after 5 years (4.3% versus 2.3%), though not after 13 years. When borderline-low levels were counted as well, the difference was statistically significant at both time points. Each additional year of metformin use was associated with a higher risk of B12 deficiency (odds ratio 1.13 per year), and neuropathy was more common among metformin users with low B12. The authors concluded that routine testing of B12 levels should be considered in people taking metformin.^[4]

How B12 is tested

Universal screening isn’t recommended, but testing should be considered in people with at least one risk factor and one clinical feature of deficiency. The starting point is a blood test for total serum B12. A level below 180 pg/mL is diagnostic of deficiency. Borderline levels (180 to 350 pg/mL) call for a methylmalonic acid (MMA) test, and an elevated MMA confirms the diagnosis.^[1] A JAMA review of peripheral neuropathy likewise lists B12 with its metabolites, blood sugar and a protein test for certain blood disorders as the recommended first tests.^[2]

Finding the cause matters too. In people without a clear reason for the deficiency, further testing for atrophic gastritis, including a test for Helicobacter pylori and autoantibodies linked to autoimmune gastritis, is advised.^[1] Your primary care physician usually orders and interprets these tests. If you are worried about your feet, it is fine to ask for the B12 check yourself.

How it is treated

Treatment is prescribed and monitored by your primary care physician or another treating clinician. A few points from the research:

• Oral B12 can be used in most people and is not inferior to intramuscular (injected) B12. Injections should be considered for severe deficiency or neurologic symptoms.^[1]
• The expert panel considered injected B12 the first choice when manifestations are acute and severe. For long-term treatment, high-dose oral B12 may be considered, and the route and dose depend on how severe the symptoms are, what caused the deficiency and what the treatment goals are.^[3]
• Among people with type 2 diabetes who take metformin, a systematic review of 7 trials with 506 participants found that B12 supplements raised blood levels. The effect on neuropathy symptoms was still unclear: two studies reported significant improvement and one reported no significant effect. The authors called for more high-quality trials.^[5]

What to expect for your nerves

Even when the cause is found and treated, nerves recover slowly. In peripheral neuropathy generally, complete reversal of nerve damage is uncommon even when treatments are available.^[2] That is another reason to have symptoms checked earlier rather than later.

Where a nerve specialist fits in

A normal or corrected B12 doesn’t always explain everything. Neuropathy in both feet can exist alongside a pinched nerve in the foot, ankle or back. A foot-focused evaluation looks for those, and helps make sure that a treatable entrapment isn’t missed. We work alongside your primary care physician, endocrinologist or neurologist. To learn more, see peripheral neuropathy, numb toes and numb toes: when to worry.

When to see a specialist

Make an appointment if you have new or worsening numbness, tingling or burning in your feet, or if you have diabetes and haven’t had a foot examination in the past year.