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Health Tips August 01, 2022

What You Should Know About Metformin And Vitamin B12

Medically Reviewed by Pharm Chioma

Written by Adaobi Oduenyi

Research has shown that people who take metformin to treat insulin resistance caused by type 2 diabetes may be at risk of developing a vitamin B12 deficiency. It is believed that metformin can lead to vitamin B12 deficiency (low vitamin B12) which if left untreated can lead to certain health problems, like anaemia and nerve damage.

What is metformin?

Metformin is a drug used to treat type 2 diabetes mellitus and to help prevent type 2 diabetes in patients at high risk of developing it. Metformin is available as immediate and modified-release tablets, as well as an oral solution.

Metformin is also used off-label to treat other health conditions, such as:

  • Prediabetes

  • Gestational diabetes

  • Weight gain from antipsychotic medications

  • Polycystic ovary syndrome (PCOS)

Why is Vitamin B12 important? 

Vitamin B12 — also known as cobalamin — is a water-soluble vitamin that helps support your body’s blood and nerve cells. It also helps your body make DNA. 

In most cases, you can get enough vitamin B12 through your diet alone. Vitamin B12 is found in a variety of foods and drinks, such as:

  • Beef

  • Seafood

  • Poultry

  • Dairy products

  • Nutritional yeast

  • Breakfast cereals

  • Plant-based milk, like almond, coconut, and soy milk

  • Vitamin B12 supplements and medications

When needed, you can take vitamin B12 (cyanocobalamin) as a dietary supplement. It’s available in oral and sublingual (under the tongue) forms to prevent and treat vitamin B12 deficiency. 

How does metformin affect vitamin B12 levels?

Research has shown that people who have been taking metformin long-term are at risk for vitamin B12 deficiency. A study published in the April 2016 Journal of Clinical Endocrinology and Metabolism looked at more than 1,000 subjects who had been taking metformin for about 12 years; of those, 13% had an increased risk of vitamin B12 deficiency. 

Another study showed that people with type 2 diabetes who took more than 1,000 milligrams (mg) of metformin for four or more years were especially at risk for a vitamin B12 deficiency. It appears that the longer someone takes metformin and the higher the daily dose of this medication, the greater the risk of developing a B12 deficiency.

“Research has shown that people who take metformin to treat insulin resistance caused by type 2 diabetes may be at risk of developing a vitamin B12 deficiency.“

Does vitamin B12 interfere with metformin?

No. Vitamin B12 supplements don’t interact with metformin, so they can safely be taken together. 

However, it’s always a good idea to keep a current list of all your medications. This helps your healthcare provider and pharmacist make sure there are no interactions to be concerned about. 

How do I know if my B12 levels are too low?

Blood tests can help determine if your vitamin B12 levels are too low. 

Vitamin B12 levels at less than 200 pg/mL generally suggest a vitamin B12 deficiency. Your healthcare provider may also check methylmalonic acid (MMA) levels in your blood or urine. Your body makes extra MMA if it doesn’t have enough vitamin B12. 

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Symptoms of vitamin B12 deficiency include: 

  • Pale skin

  • Feeling weak or tired

  • Dizziness

  • Fast or irregular heartbeat

  • Tingling in the feet and hands (nerve pain)

  • Shortness of breath

Contact your healthcare provider if you’re experiencing any of these symptoms so that they can check your vitamin B12 levels.

What can you do?

  • If you have been taking metformin for several years, ask your health care provider to have your vitamin B12 level measured, and ask what your level should be.

  • If you have symptoms of a vitamin B12 deficiency, including neuropathy, let your provider know and ask to have your B12 level measured.

  • If your level is below target, talk with your provider about treatment options. You may be able to take a daily B12 supplement, for example, rather than receiving B12 injections.

  • Certain medications can affect B12 levels, so list out all your medications for your healthcare provider.

  • Because older adults are at risk of a vitamin B12 deficiency, it is important to start getting regular blood tests for this when you are in your 60s. Some health experts recommend that older adults take a daily B12 supplement.

  • Eat foods that contain vitamin B12. If you follow a vegetarian, focus on eating foods fortified with vitamin B12 or consider taking a multivitamin.

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