Vitamin B12 Deficiency Symptoms: Metformin and Diabetes Guide

Could tingling feet have a cause other than diabetes?

If you have type 2 diabetes and have used metformin for years, new tingling or numbness in your feet might seem like an inevitable complication of diabetes. Yet vitamin B12 deficiency can produce similar nerve symptoms. Both problems can also occur together.

Vitamin B12 supports healthy blood-cell production and nervous-system function. Deficiency can develop gradually and may cause neurological symptoms even without obvious anaemia. Seeking assessment early matters because prolonged deficiency can sometimes cause lasting nerve damage.

Common symptoms of vitamin B12 deficiency

Symptoms vary; not everyone develops all of them, and some people initially have none.

Rapidly worsening weakness, severe balance problems, confusion or significant breathlessness warrants prompt medical attention.

How does metformin affect B12?

Metformin remains an important and effective medicine for type 2 diabetes. However, prolonged use can reduce B12 absorption in some patients. The UK's Medicines and Healthcare products Regulatory Agency (MHRA) classifies reduced B12 as a common adverse drug reaction that may affect up to 1 in 10 people. This is not a prediction of any individual's risk.

Longer treatment duration, higher doses, low starting B12 and additional absorption or dietary risk factors may increase the likelihood. MHRA advises testing people who develop unexplained anaemia or new neuropathy and considering periodic monitoring when risk factors exist.

Do not stop metformin on your own. A clinician can assess and treat the deficiency while reviewing your diabetes care.

What did the Bangladesh study find?

A study involving 100 adults with type 2 diabetes at a Sylhet hospital compared two groups of 50 patients each.

The finding supports an association, but this was a small, single-centre study. Its percentages should not be generalized to every person with diabetes in Bangladesh.

B12 deficiency or diabetic neuropathy?

Both may cause burning, tingling or numbness in the feet. Symptoms alone cannot reliably distinguish them. If you take metformin long-term and develop new or worsening nerve symptoms, your clinician may assess serum B12 alongside glucose control and other possible causes.

Correcting a B12 deficiency can help with symptoms caused by that deficiency, but it does not necessarily reverse nerve damage caused by diabetes. Foot protection and assessment remain important.

Which blood tests and B12 levels matter?

Serum total B12 is commonly the first test, while active B12 may be useful in selected cases. Results should be interpreted using the reporting laboratory's validated reference ranges, symptoms and clinical context.

MedlinePlus lists 299–1054 pg/mL as an example laboratory normal range. NICE guidance instead uses diagnostic interpretation thresholds for total B12: below 180 pg/mL suggests confirmed deficiency, 180–350 pg/mL is indeterminate, and above 350 pg/mL makes deficiency less likely. These are not contradictory universal lab ranges; they answer different questions.

If results are borderline or symptoms remain concerning, a clinician may request methylmalonic acid (MMA). CBC can identify anaemia or enlarged red blood cells, but a normal CBC does not exclude B12 deficiency.

Who else is at risk?

Other risk factors include strict vegan diets without fortified food, long-term proton pump inhibitor treatment, autoimmune gastritis, Crohn's disease, certain stomach or intestinal surgeries and reduced absorption with age. If a medicine may be contributing, review it with your clinician rather than stopping it yourself.

Food sources and treatment

Fish, meat, eggs, milk and dairy products contain B12. Fortified foods may help people who avoid animal products. Food alone may be insufficient when the problem is poor absorption.

Treatment depends on the cause, test results and neurological symptoms. A clinician should choose the replacement approach and duration. Do not start an injection regimen or change metformin dosage based on an online article.

When should you seek medical advice?

Ask about testing if you take metformin long-term and develop unexplained fatigue, new tingling, numbness, balance difficulties or a sore tongue. Seek prompt care if neurological function worsens quickly, walking becomes unsafe, or you develop confusion or significant breathlessness.

For many people, a simple question at a diabetes follow-up is a useful start: “Given my medication and symptoms, should I have a vitamin B12 test?”

Frequently asked questions

What are common signs of B12 deficiency?

Unusual tiredness, tingling, numbness, a sore tongue, memory difficulties or balance problems may occur.

Can metformin lower vitamin B12?

Yes. Long-term use can impair B12 absorption in some patients; MHRA says reduced levels may affect up to 1 in 10 users.

Should I stop metformin if B12 is low?

No. Do not stop or change metformin without discussing it with your clinician.

What is a normal B12 level?

Ranges and diagnostic cut-offs vary. MedlinePlus lists 299–1054 pg/mL as a reference range, while NICE uses separate diagnostic thresholds.

Should tingling feet in diabetes prompt B12 testing?

A clinician may consider B12 testing, especially with long-term metformin use or new neuropathy symptoms.

Which foods provide B12?

Fish, meat, eggs, dairy products and appropriately fortified foods are sources.

Can B12 deficiency occur without anaemia?

Yes. A normal CBC or absence of anaemia does not rule it out.

How often should someone on metformin test B12?

There is no single interval for everyone; symptoms and individual risk factors guide the decision.

References

1. MHRA metformin and B12
2. Bangladesh Journal of Medicine study
3. NICE B12 guidance
4. MedlinePlus vitamin B12 level
5. NHS symptoms
6. NHS causes

This article is for general health education and does not replace personal medical assessment.