About 1 in 4 Vietnamese patients with type 2 diabetes taking metformin have low vitamin B12 levels, according to a 2026 cross-sectional study of 400 patients. Gram Research analysis shows that patients taking metformin for more than 5 years were 1.84 times more likely to develop B12 deficiency, and those with anemia faced 3.43 times higher risk. Regular B12 testing may help catch this problem early in long-term metformin users.
A new study of 400 Vietnamese patients with type 2 diabetes found that about 1 in 4 people taking metformin had low vitamin B12 levels. Gram Research analysis shows that patients who took metformin for more than 5 years were nearly twice as likely to develop B12 deficiency, and those with anemia faced even higher risk. Vitamin B12 is essential for nerve function and energy, so doctors may want to check B12 levels regularly in patients on long-term metformin therapy. The findings suggest that simple blood tests could help catch this problem early.
Key Statistics
A 2026 cross-sectional study of 400 Vietnamese patients found that 25.75% of people taking metformin for type 2 diabetes had low vitamin B12 levels, including 7.25% with severe deficiency and 18.50% with borderline low levels.
Patients taking metformin for more than 5 years were 1.84 times more likely to have vitamin B12 deficiency compared to those on shorter-term therapy, according to the 2026 study of 400 diabetic patients.
Among 400 metformin-treated diabetic patients in a 2026 study, those with anemia had 3.43 times higher odds of vitamin B12 deficiency than patients without anemia.
The Quick Take
- What they studied: How often vitamin B12 deficiency occurs in people with type 2 diabetes taking metformin, and what factors increase the risk.
- Who participated: 400 Vietnamese patients with type 2 diabetes who had been taking metformin for at least 6 months. Participants were recruited from two hospitals in Thai Binh, Vietnam.
- Key finding: About 26% of patients had low B12 levels. Those taking metformin for more than 5 years were 1.84 times more likely to have low B12, and patients with anemia were 3.43 times more likely to have the deficiency.
- What it means for you: If you take metformin for diabetes, especially for longer than 5 years, ask your doctor about checking your B12 levels. Low B12 can cause fatigue, numbness, and nerve problems. Regular testing may help catch problems early, though more research is needed to confirm the best testing schedule.
The Research Details
Researchers recruited 400 patients with type 2 diabetes from two hospitals in Vietnam who had been taking metformin for at least 6 months. They measured each patient’s vitamin B12 level in the blood and collected information about how long they had been taking metformin, whether they had anemia, and other health factors. They then analyzed which factors were most strongly linked to low B12 levels. This type of study, called a cross-sectional study, takes a snapshot of a group at one point in time rather than following people over months or years.
This research approach is useful for identifying how common a problem is and what risk factors might be involved. By studying a large group of real patients in actual hospital settings, the researchers could see patterns that might not show up in smaller studies. However, because this is a snapshot rather than a long-term follow-up, it cannot prove that metformin directly causes B12 deficiency, only that the two are connected.
The study included a reasonably large sample of 400 patients, which provides fairly reliable numbers about how common the problem is. However, all participants came from just two hospitals in one region of Vietnam, so results may not apply equally to other populations. The researchers used statistical methods to adjust for other factors that might affect B12 levels, which strengthens the findings. The study authors note that their adjusted findings are exploratory and do not prove cause and effect.
What the Results Show
Among the 400 patients studied, 103 people (about 26%) had low vitamin B12 levels. Of these, 29 patients (7%) had severe deficiency, while 74 patients (19%) had borderline low levels. The researchers found two main risk factors: patients who had taken metformin for more than 5 years were about 1.8 times more likely to have low B12, and patients with anemia were about 3.4 times more likely to have low B12. These associations remained even after the researchers adjusted for other health factors that might affect B12 levels.
The study looked at whether macrocytosis, a condition where red blood cells become abnormally large, was linked to low B12. However, the data on this was not precise enough to draw firm conclusions. The researchers noted that unexplained anemia or nerve symptoms (like tingling or numbness) should prompt doctors to check B12 levels, regardless of how long a patient has been taking metformin.
Previous research has suggested that metformin can interfere with vitamin B12 absorption in the stomach. This study confirms that low B12 is indeed common in metformin users, with a rate of about 26% compared to lower rates in people not taking the medication. The finding that longer use increases risk aligns with earlier studies suggesting that B12 problems develop gradually over time with metformin therapy.
This study has several important limitations. All participants came from just two hospitals in one Vietnamese province, so the results may not apply to other countries or populations. The study was a snapshot in time, not a long-term follow-up, so researchers cannot prove that metformin causes B12 deficiency, only that they are associated. The researchers used convenience sampling rather than random selection, which could introduce bias. The study authors emphasize that their findings are exploratory and do not establish definite cause and effect relationships.
The Bottom Line
People with type 2 diabetes taking metformin, especially those on the medication for more than 5 years, should discuss B12 testing with their doctor. There is moderate evidence that periodic B12 checks are reasonable during long-term metformin use. If you experience fatigue, numbness, tingling, or other nerve symptoms, ask your doctor to check your B12 level. Some doctors may recommend B12 supplements or dietary changes for patients on long-term metformin, though individual decisions should be made with your healthcare provider.
This research is most relevant to people with type 2 diabetes taking metformin, particularly those who have been on the medication for more than 5 years. People with existing anemia should be especially attentive to B12 status. Healthcare providers managing diabetic patients on metformin should consider periodic B12 screening. People without diabetes or those not taking metformin do not need to worry about these specific findings.
B12 deficiency develops gradually over time, often without obvious symptoms at first. Serious symptoms like nerve damage can take months or years to develop. Regular testing allows doctors to catch low B12 before symptoms become severe. If deficiency is found, B12 supplements or dietary changes can usually correct the problem within weeks to months.
Frequently Asked Questions
Does metformin cause vitamin B12 deficiency?
Metformin is associated with low B12 levels, particularly after 5 years of use. A 2026 study of 400 patients found 26% had low B12. However, the study cannot prove metformin directly causes deficiency, only that they are connected.
How often should I get my B12 checked if I take metformin?
The 2026 research suggests periodic B12 testing during long-term metformin therapy, with 5 years of use as a practical reminder to check. Discuss specific testing schedules with your doctor based on your individual risk factors.
What are symptoms of B12 deficiency I should watch for?
Common symptoms include fatigue, weakness, numbness or tingling in hands and feet, and difficulty concentrating. The 2026 study notes that unexplained anemia or nerve symptoms warrant B12 assessment, regardless of metformin duration.
Can I prevent B12 deficiency while taking metformin?
Regular B12 testing allows early detection. Some doctors recommend B12 supplements or dietary sources like meat, fish, eggs, and fortified cereals for long-term metformin users. Discuss prevention strategies with your healthcare provider.
Is B12 deficiency serious if I have diabetes?
Untreated B12 deficiency can cause nerve damage, anemia, and cognitive problems. The 2026 study found anemia increased deficiency risk 3.43 times, suggesting these conditions interact. Early detection through testing prevents serious complications.
Want to Apply This Research?
- Set a reminder to track your B12 test results annually if you have been taking metformin for more than 5 years. Log the date of your test and the result (measured in pg/mL) to monitor trends over time.
- If your doctor recommends B12 supplementation, use the app to set a daily reminder for taking your supplement. Track any symptoms like fatigue or numbness to share with your healthcare provider at your next visit.
- Create a health timeline in the app documenting your metformin use duration, B12 test dates and results, and any symptoms. This helps you and your doctor identify patterns and decide whether more frequent testing is needed.
This article summarizes research findings and is not medical advice. Vitamin B12 deficiency is a medical condition that requires professional diagnosis and treatment. If you take metformin or have symptoms of B12 deficiency such as fatigue, numbness, or nerve pain, consult your doctor or healthcare provider before making any changes to your medication or starting supplements. Do not stop taking metformin without medical guidance. Individual treatment decisions should be made with your healthcare team based on your specific health situation.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.