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Metformin and low vitamin B12: what you need to know | CION Cancer Clinics
Yes, long-term metformin can lower vitamin B12 in some people. It does not happen to everyone, and it is not a reason to stop your diabetes medicine. Low B12 can cause tingling feet, unsteady walking and tiredness that are easily blamed on diabetes. A simple blood test finds it, and your doctor can replace it. This page explains who is at risk and what to ask. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- Does metformin lower vitamin B12?
- Who on metformin is more likely to run low on B12?
- Is the tingling from low B12 or from diabetes?
- How is B12 checked if you take metformin?
- What do the words on your B12 report mean?
- What do people on metformin often get wrong?
- What should you ask, and what can this page not tell you?
- Common questions about metformin and B12
The short answer
Does metformin lower vitamin B12?
Yes, in some people. Taking metformin for a long time can slowly lower the amount of vitamin B12 in your blood. That is not a reason to stop your diabetes medicine. It is a reason to have your B12 checked.
How metformin gets in the way
B12 from food is absorbed at the end of the small bowel. That step needs calcium and a carrier protein made in the stomach. Metformin seems to interfere with how the bowel lining takes up the B12 and its carrier. The effect is small at first. Over years, the body's store of B12 in the liver can run down.
Why it matters for people with diabetes
Low B12 can cause tingling, numbness and burning in the feet. Diabetes can cause exactly the same symptoms. When both are present, low B12 is easy to miss, because the doctor and the family assume it is the diabetes. The difference is that nerve damage from low B12 is treatable if it is found.
Who is not at much risk
Someone who has only recently started metformin, eats milk, curd or eggs daily, and has no nerve symptoms is unlikely to be short of B12 because of the medicine alone. Checking is still reasonable after some years of use.
Never stop, skip or reduce metformin because of this page. Uncontrolled sugar causes far more harm. Your doctor decides any change.Higher chance
Who on metformin is more likely to run low on B12?
The risk is not the same for everyone. It builds when more than one of these apply.
Long-term use
The longer you have taken metformin, and the higher the amount your doctor has prescribed, the more likely your B12 store has run down. Many people in India have been on it for a decade or more.
A vegetarian diet
B12 comes almost only from animal foods. A diet with little milk, curd or eggs already starts with a small store, so a medicine that reduces absorption tips it over sooner.
Acid-reducing medicines
Stomach acid helps free B12 from food. Long-term use of medicines for acidity adds a second hurdle on top of metformin.
Often prescribed as
- Omeprazole, pantoprazole and similar
- Ranitidine-type acid blockers
Older age and gut problems
Stomach acid falls with age. Past stomach or bowel surgery, and immune conditions of the stomach or coeliac disease, also reduce absorption.
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Is the tingling from low B12 or from diabetes?
More in keeping with low B12
More in keeping with diabetes
Unsteady walking and poor balance, worse in the dark
Burning or numb feet, balance often better kept
Tiredness, pale skin, a sore red tongue
Sugar readings often high for a long time
Memory problems or low mood appearing alongside
Eye or kidney changes often present too
Large red cells on the blood report
Blood cell size usually normal
Getting checked
How is B12 checked if you take metformin?
Tell your doctor what you notice
Mention tingling, numbness, unsteady walking, tiredness or memory change, even if they seem minor. Say how long you have been on metformin and whether you eat milk, curd or eggs.
A B12 blood test and blood count
The B12 level shows how much is circulating. The complete blood count shows your haemoglobin and the size of your red cells. Folate is usually checked at the same time.
Extra tests if the result is borderline
B12 results in the grey zone are common. Your doctor may add MMA or homocysteine, which rise when the body is truly short of B12.
A plan from your treating doctor
If B12 is low, your doctor decides how to replace it and when to recheck. Metformin is usually continued. Checks are often repeated from time to time while you stay on it.
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On your report
What do the words on your B12 report mean?
- Serum B12 or cobalamin
- The B12 level in your blood. Reference ranges differ between laboratories, and a single value is read alongside symptoms and repeat tests.
- Borderline or low-normal
- A result near the lower limit. It does not settle the question either way, which is why further tests may follow.
- MCV
- The average size of your red cells. A high value fits low B12 or folate, but alcohol, thyroid and liver problems also raise it.
- MMA and homocysteine
- Substances that build up when cells lack B12. Kidney problems, common in long-standing diabetes, can raise them too.
- Macrocytosis
- Larger than usual red cells. It is a finding, not a diagnosis.
Commonly believed
What do people on metformin often get wrong?
"Metformin is damaging my nerves, so I should stop it."
Metformin does not damage nerves directly. It can lower B12 over time, and low B12 can. The answer is to check and replace B12, not to stop a medicine that protects you from the harm high sugar does.
"Tingling feet are just part of diabetes."
They often are. But when you take metformin, low B12 is a treatable cause hiding behind the same symptom. A blood test is simple and worth asking for.
"A multivitamin covers it, so no test is needed."
Many multivitamins carry only small amounts of B12, and absorption is the problem here. Without a test, you do not know whether your level is adequate or whether something else is causing symptoms.
"My B12 was normal once, so I never need it checked again."
The store runs down slowly over years. A normal result some years ago says little about today, especially if new symptoms have appeared.
Being straight with you
What should you ask, and what can this page not tell you?
Low B12 in someone on metformin is common and usually simple to manage. The hard part is noticing it. Take these questions to your next diabetes review.
Questions worth asking
Has my B12 been checked since I started metformin? Could my tingling or tiredness be from low B12 rather than sugar? Do my acidity tablets add to the risk? If my level is low, how will it be replaced, and when will it be rechecked?
When to see a haematologist
Most people are managed by their physician or diabetologist. A haematologist, a blood specialist, helps when the haemoglobin is very low, when white cells or platelets are also low, when the red cells stay large after B12 is replaced, or when the cause is unclear.
What this page cannot tell you
It cannot tell you whether your symptoms come from B12, diabetes or something else, or what your own result means. That needs your reports, an examination and sometimes repeat tests. CION's haematology team can review your blood reports and explain the next step.
Questions we are asked
Common questions about metformin and B12
Should I stop metformin if my B12 is low?
No, not on your own. For most people the benefits of metformin for blood sugar far outweigh this side effect, and low B12 can be replaced. Your doctor will decide whether any change is needed. Stopping suddenly can let your sugar rise, which brings its own harm to nerves, eyes and kidneys.
How often should B12 be checked on metformin?
There is no single rule everyone follows. Many diabetes guidelines suggest checking from time to time in people on long-term metformin, and sooner if tingling, numbness, tiredness or a low haemoglobin appear. Ask your doctor to add it to your regular diabetes blood tests.
Can I just take a B12 tablet without testing?
It is better to test first. A result before treatment shows whether you were truly low and gives a baseline to compare against. Taking B12 first can make later tests hard to read. Discuss any supplement with your doctor, who will choose the form and amount that suits you.
Will the tingling go away once B12 is replaced?
Nerve symptoms caused by low B12 often improve, but slowly, over months. Damage present for a long time may not fully recover. If diabetes is also affecting the nerves, some symptoms may remain. Good sugar control and foot care stay important either way.
Does the extended-release form of metformin avoid this?
There is no clear evidence that one form of metformin avoids the effect on B12. What matters more is how long you have taken it and your other risks. Do not switch forms for this reason without speaking to your doctor.
Can low B12 from metformin affect my blood count?
Yes. If B12 falls far enough, the bone marrow makes fewer and larger red cells, and haemoglobin drops. You may feel tired or breathless. Nerve symptoms can come before any change in the blood count, so a normal count does not rule out low B12.
My parent is vegetarian and on metformin. What should we do?
Ask their doctor for a B12 test at the next review, especially if they have tingling feet, unsteady walking, memory change or tiredness. A vegetarian diet and long-term metformin together raise the chance of low B12. Bring their list of medicines, including acidity tablets.
Is low B12 on metformin a sign of blood cancer?
Low B12 in someone on metformin usually has a simple explanation. Blood cancer is not the likely cause. If your blood cells stay abnormal after B12 is replaced, or other counts are also low, your doctor will look further, often with a haematologist.
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Sources
- NHS — Metformin
- NHS — Vitamin B12 or folate deficiency
- NICE — B12 and folate deficiency (Clinical Knowledge Summary)
- NIH Office of Dietary Supplements — Vitamin B12 fact sheet for consumers
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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