Metformin is one of the most commonly prescribed medications for managing type 2 diabetes. While it is generally well tolerated and effective, long-term use can reduce vitamin B12 levels in some people. Understanding the connection between metformin and vitamin B12 can help you recognize potential symptoms and know when to speak with your healthcare team.
Article highlights
- Metformin is one of the most commonly used medications for type 2 diabetes.
- Long-term metformin use may affect vitamin B12 levels.
- Vitamin B12 plays several important roles in the body.
- Some symptoms of vitamin B12 deficiency can be easy to overlook.
- Certain people taking metformin may need regular B12 monitoring.
- It is important to talk with your healthcare provider before stopping metformin.
What is vitamin B12 and why is it important?
Vitamin B12 is an essential vitamin that your body needs to make healthy red blood cells, maintain normal nerve function and produce DNA. As your body cannot produce vitamin B12 on its own, you need to get it from food or supplements.
When you do not have enough vitamin B12, your body may have difficulty producing healthy red blood cells. Low levels can also affect the nervous system. If a deficiency is left untreated for months to years, some nerve-related problems, such as numbness, tingling, or balance issues, can become more difficult to reverse.
Can metformin cause vitamin B12 deficiency?
Yes, over time, Metformin is known to interfere with the absorption of vitamin B12 in the digestive system. As a result, people who take metformin may have lower vitamin B12 levels over time, particularly after several years of use.
Not everyone who takes metformin will develop a vitamin B12 deficiency. However, the risk appears to increase with longer-term use and higher cumulative exposure to metformin.
What are symptoms of low vitamin B12?
Vitamin B12 deficiency can develop gradually, and some people may not notice symptoms at first. Possible signs include:
- Feeling tired or weak
- Pale skin
- A sore or swollen tongue
- Numbness or tingling in the hands or feet
- Muscle weakness
- Problems with balance or coordination
- Changes in memory or concentration
Some of these symptoms can have many different causes. For example, numbness or tingling may also be associated with diabetes-related nerve damage.That’s why it is important not to assume that symptoms are caused by vitamin B12 deficiency.
Who is most at risk of low vitamin B12 while taking metformin?
Although anyone taking metformin can develop low vitamin B12 levels, the risk may be greater if you:
- Have been taking metformin for a long period of time
- Take a higher dose of metformin
- Have a diet that is low in vitamin B12
- Are older (especially adults aged 65 years and older)
- Have a condition that affects vitamin B12 absorption, such as Crohn’s disease, celiac disease, anemia, and gastritis
- Have had certain gastrointestinal surgeries or conditions
- Take other medications that can affect vitamin B12 absorption, such as proton pump inhibitors (e.g. omeprazole or pantoprazole), or H2-receptor blockers (e.g. famotidine)
How often should your vitamin B12 levels be checked?
Vitamin B12 levels should be measured periodically in people taking metformin, as well as in people who develop signs or symptoms of vitamin B12 deficiency, such as impaired sensation or peripheral neuropathy.
There is no single testing schedule that is right for everyone. Your healthcare provider can determine how often your levels should be checked based on factors such as your metformin dose, how long you’ve been taking it, your symptoms, diet and other risk factors.
How is low vitamin B12 managed?
If testing confirms that your vitamin B12 level is low, treatment depends on the severity of the deficiency and why it developed. For people with a mild deficiency, increasing vitamin B12 through food and/or an oral supplement may be appropriate. Vitamin B12 is naturally found in foods such as fish, meat, poultry, eggs, milk, yogurt and cheese. It is also found in fortified foods, such as some plant-based beverages, breakfast cereals and nutritional yeast.
Eating more vitamin B12-rich foods can help you meet your daily nutritional needs, but food alone may not be enough, particularly when the body has difficulty absorbing B12. In these cases, a vitamin B12 supplement may be recommended either orally or via injection.
For many people, oral vitamin B12 supplements are effective at increasing B12 levels. But for those with severe deficiency or problems absorbing vitamin B12, a healthcare provider may recommend vitamin B12 injections. Treatment and the duration of supplementation will depend on the underlying cause and severity of the deficiency.
Are vitamin B12 supplements recommended for everyone taking metformin?
No. Taking metformin does not automatically mean that you need to take a vitamin B12 supplement. Metformin can increase the risk of vitamin B12 deficiency, so it is recommended that B12 levels be measured periodically in people taking metformin, or when symptoms of deficiency occur.
If testing shows that your vitamin B12 level is low, your healthcare provider can determine whether supplementation is appropriate and which type of treatment is best for you.
When should you talk to your healthcare provider?
It’s time to speak to your healthcare provider if you:
- Experience unusual or persistent fatigue or weakness
- Develop numbness or tingling in your hands or feet
- Notice problems with balance, coordination, memory or concentration
- Have other symptoms that could suggest vitamin B12 deficiency
- Have been taking metformin for a long time and have never had your B12 level checked
- Have other risk factors for B12 deficiency (e.g., a diet low in B12-containing foods or a condition that affects B12 absorption)
- Have questions about whether you should take a vitamin B12 supplement
Your healthcare provider can determine whether a blood test is appropriate and recommend treatment if your B12 level is low. This is particularly important because some symptoms of B12 deficiency (e.g., numbness and tingling), can overlap with other condition such as diabetic neuropathy. Testing can help determine the underlying cause of symptoms and ensure that the appropriate treatment is provided.
Your 3-step action plan to reducing B12 deficiencies
Step 1: Know the signs: Learn the symptoms of vitamin B12 deficiency, including fatigue, weakness, numbness and tingling, and changes in balance or coordination.
Step 2. Ask about testing: If you take metformin long term, have symptoms, or have other risk factors for B12 deficiency, ask your healthcare provider whether your vitamin B12 level should be checked.
Step 3. Keep taking your medication as prescribed: Do not stop or change your metformin dose on your own. If you have concerns about vitamin B12, talk with your healthcare provider about monitoring and treatment options.
Metformin remains an important medication for many people living with type 2 diabetes, and its benefits generally outweigh the potential risk of vitamin B12 deficiency. Being aware of this possible side effect, and discussing appropriate monitoring methods with your healthcare team, can help you stay on top of your health while continuing to manage your diabetes effectively.
