Should diabetics take vitamin B12? Exploring the link to metformin

October 21, 2025 •

4 min read

According to a 2009 study, approximately 22% of people with type 2 diabetes were low in vitamin B12, a risk often heightened by long-term metformin use. This creates a critical situation where a B12 deficiency can compound existing diabetic complications, particularly nerve damage.

Quick Summary

Diabetics, especially those on metformin therapy, face an increased risk of vitamin B12 deficiency, which can cause or worsen neuropathy. Regular screening and, if necessary, medically supervised supplementation can help manage this risk and prevent serious complications.

Key Points

Metformin-induced deficiency: The long-term use of metformin, a common diabetes drug, can interfere with B12 absorption, increasing the risk of deficiency.
Neuropathy risk: Both diabetes and B12 deficiency can cause nerve damage (neuropathy), and the symptoms can overlap, making diagnosis complex.
Monitoring is key: Guidelines from the American Diabetes Association recommend periodic monitoring of B12 levels for diabetic patients on metformin, particularly those with nerve issues or anemia.
Oral vs. injection: If a deficiency is confirmed, treatment can involve either oral supplements or intramuscular injections, both of which are effective.
Dietary support: While not sufficient for all, increasing consumption of animal products and fortified foods can help support B12 levels.
Consult your doctor: Due to overlapping symptoms and individual risk factors, all decisions regarding B12 testing and supplementation must be made in consultation with a healthcare professional.

The Metformin-B12 Connection

Metformin is a first-line medication for millions of people with type 2 diabetes. It works by decreasing glucose production in the liver and increasing insulin sensitivity. However, decades of research have established a clear association between long-term metformin use and decreased vitamin B12 levels. The risk of developing a deficiency increases with both higher doses and longer duration of treatment.

The mechanism behind this interaction is multifaceted, but one primary reason is that metformin interferes with the absorption of vitamin B12 in the gut. It is thought to affect the calcium-dependent binding of the B12-intrinsic factor complex, which is necessary for the vitamin's uptake. This disruption can lead to a gradual but significant depletion of the body's B12 stores.

Factors increasing the risk of B12 deficiency

While metformin is a major contributor, several other factors can increase a diabetic's risk of B12 deficiency. These include:

Dietary choices: Since vitamin B12 is found almost exclusively in animal products, those following vegan or vegetarian diets are at high risk.
Increasing age: The body's ability to absorb vitamin B12 naturally decreases with age.
Other medications: Certain drugs, like proton pump inhibitors (PPIs) used for acid reflux, can also interfere with B12 absorption.
Gastric issues: Conditions like Crohn's disease or previous bariatric surgery can impact absorption, regardless of medication use.

Overlapping Symptoms: A Diagnostic Challenge

Both diabetes and vitamin B12 deficiency can independently cause nerve damage, a condition known as neuropathy. This overlap can create a significant diagnostic challenge for healthcare providers and patients. The symptoms can be eerily similar, making it difficult to distinguish whether they are caused by high blood sugar or low B12.

Symptoms of vitamin B12 deficiency include:

Tingling and numbness in the hands and feet
Fatigue and weakness
Balance and coordination problems
Memory loss and cognitive impairment
Sore tongue and mouth ulcers
Megaloblastic anemia, a blood disorder

When a diabetic patient on metformin experiences these neurological symptoms, it is crucial to investigate both blood glucose control and B12 status. Failure to treat a B12 deficiency can lead to worsening nerve damage that may become irreversible over time.

Comparison of B12 Deficiency and Diabetic Neuropathy Symptoms


Symptom	Primary Cause	Potential Overlap	Distinguishing Features	Diagnosis	Treatment
Numbness & Tingling	Both	High sugar levels damaging nerves; Low B12 affecting nerve sheaths.	Gradual onset often starting in feet (diabetic neuropathy); Can appear anywhere (B12 deficiency).	Blood tests for B12, nerve conduction studies.	B12 supplementation for deficiency; Blood sugar control for diabetes.
Fatigue & Weakness	Both	Anemia from B12 deficiency; High blood sugar disrupting energy.	Anemia often accompanied by pale skin (B12 deficiency); Fatigue is a general diabetes symptom.	Blood tests for B12 and complete blood count.	B12 supplementation if deficient; Diabetes management.
Balance Problems	Both	Severe B12 deficiency; Advanced diabetic neuropathy affecting proprioception.	Specific gait changes may indicate spinal cord involvement (B12); Falls risk often higher with neuropathy.	Blood tests, neurological exam.	B12 treatment; Physical therapy.
Cognitive Changes	B12 Deficiency	Can overlap with diabetes-related cognitive decline.	Memory loss, confusion, and mood changes are common in B12 deficiency.	Blood tests for B12 and MMA.	B12 supplementation.

Screening, Treatment, and Diet

The American Diabetes Association recommends that healthcare providers periodically monitor B12 levels in patients taking metformin, especially those with neuropathy or anemia. While not every metformin user will develop a deficiency, regular checks are a proactive measure to catch any decline early. A more sensitive and specific test for B12 status measures methylmalonic acid (MMA) or holotranscobalamin.

If a deficiency is confirmed, treatment is straightforward and highly effective. The two primary options are oral supplements or intramuscular injections.

Oral Supplements: High-dose oral B12 tablets are a highly effective option for many individuals.
Injections: Injections are a common and effective treatment, particularly in severe cases.

Correcting a B12 deficiency is known to alleviate associated neuropathic and anemic symptoms. It is essential for patients to work with their doctor to determine the right form and regimen of supplementation. It is crucial not to stop metformin therapy without consulting a healthcare provider first.

Dietary sources of vitamin B12

Increasing dietary intake is an important step, though it may not be sufficient for those with impaired absorption. Good sources include:

Red meat (beef, ham)
Fish (salmon, tuna)
Dairy products (milk, yogurt, cheese)
Eggs
Fortified foods (cereals, nutritional yeast)

Conclusion

So, should diabetics take vitamin B12? The answer is often yes, especially for those on long-term, high-dose metformin therapy or those with other risk factors for deficiency. The potential for B12 deficiency to cause or worsen neuropathy and other health issues makes regular monitoring a critical part of comprehensive diabetes care. Anyone with diabetes, particularly those experiencing unexplained fatigue, tingling, or memory issues, should proactively discuss B12 testing with their doctor. Early detection and treatment can prevent the progression of serious, irreversible complications and significantly improve a person's quality of life.

Consulting a healthcare professional is the most important step to determine the right course of action based on individual health needs, risk factors, and test results. For those requiring supplementation, effective oral and injectable treatments are readily available, and a balanced diet rich in B12 is always a supportive measure. For more information on diabetes management, visit the American Diabetes Association website.

Disclaimer: This information is for general knowledge and should not be taken as medical advice. Consult with a healthcare professional before making any decisions about your health or treatment, including whether to take vitamin B12.

Frequently Asked Questions

Yes, research confirms that long-term use of metformin can interfere with the body's absorption of vitamin B12, increasing the risk of deficiency. The risk is higher with higher doses and longer treatment duration.

Common symptoms include fatigue, weakness, numbness or tingling in the hands and feet, balance problems, memory issues, and a sore or red tongue. Some of these can overlap with symptoms of diabetic neuropathy.

The specific type and form of B12 supplementation, whether oral or injectable, should be determined by a healthcare professional based on individual needs and the severity of the deficiency.

Some studies suggest that B12 supplementation can improve neuropathic symptoms and reduce pain in patients with diabetic neuropathy, especially when a deficiency is also present. However, supplementation is not a replacement for proper diabetes management.

Excellent food sources include meat, fish, poultry, eggs, and dairy products. For vegans or vegetarians, fortified foods like some cereals and nutritional yeast are important sources.

The American Diabetes Association recommends that people on metformin, particularly those with nerve damage or anemia, have their B12 levels periodically monitored. Your doctor can determine the right frequency for you.

No. You should not stop your metformin medication without consulting your doctor first. B12 deficiency can be managed with supplements while you continue your diabetes treatment.