Metformin-Caused Vitamin B12 Deficiency Could Be Causing Nerve Damage!


The number one most prescribed drug to treat people with type 2 diabetes may actually be causing irreversible nerve damage in many patients.

Metformin, also known as Glucophage, is prescribed to more than 120 million patients worldwide. It works by reducing the amount of glucose produced by the liver as well as increasing a patient’s sensitivity to insulin.

A recent study confirms a concern the medical world has been aware of for quite a few years:


Metformin is causing varying degrees of vitamin B12 deficiency in approximately 10 percent of prescribed patients.


The research was done by Dr. Kaenat Mulla and colleagues at Hucknall Road Medical Centre in Nottingham.

The researchers conducted an audit of vitamin B12 screening and deficiency among female patients with type 2 diabetes who were taking metformin.

“The audit findings indicated that 64 percent of patients had not had their vitamin B12 levels checked at all, and that 9.6 percent of patients were deficient but only 6.4 percent were being treated with vitamin B12,” a press release from the study states.


Why You Need B12

Vitamin B12 is essential to your nervous system.


Vitamin B12 plays a critical role in the development and function of brain and nerve function.  The significant concern is that:


Even a patient who’s blood sugars are well managed could experience severe and permanent nerve damage as a result of metformin-induced B12 deficiency.


That’s because vitamin B12 is essential to the formation and maintenance of the myelin sheath — a fatty substance that protects your central and peripheral nervous system.

For people with diabetes who take metformin, that permanent nerve damage could easily be incorrectly diagnosed as peripheral neuropathy — a known complication of high blood sugars in people with diabetes.

“Nerve damage in the periphery (e.g. face, limbs, organs),” explained the press release, “is a common complication of diabetes, with symptoms that range from numbness to pain, and can lead to debilitating loss of balance and coordination.”


Peripheral Neuropathy


Peripheral nerves make up an intricate network, connecting the brain and spinal cord to the muscles, skin, and internal organs.


Peripheral neuropathy, a result of damage to your peripheral nerves, often causes weakness, numbness and pain, usually in your hands and feet. It can also affect other areas of your body.

Your peripheral nervous system sends information from your brain and spinal cord (central nervous system) to the rest of your body. Peripheral neuropathy can result from traumatic injuries, infections, metabolic problems, inherited causes and exposure to toxins. One of the most common causes is diabetes mellitus.

People with peripheral neuropathy generally describe the pain as stabbing, burning or tingling. In many cases, symptoms improve, especially if caused by a treatable condition. Medications can reduce the pain of peripheral neuropathy.


Symptoms of Peripheral Neuropathy



Every nerve in your peripheral system has a specific function, so symptoms depend on the type of nerves affected.

Nerve Classifications

  • Sensory nerves that receive sensation, such as temperature, pain, vibration or touch, from the skin
  • Motor nerves that control muscle movement
  • Autonomic nerves that control functions such as blood pressure, heart rate, digestion and bladder


Peripheral Neuropathy Signs and Symptoms

  • Gradual onset of numbness, prickling or tingling in your feet or hands, which can spread upward into your legs and arms
  • Sharp, jabbing, throbbing, freezing or burning pain
  • Extreme sensitivity to touch
  • Lack of coordination and falling
  • Muscle weakness or paralysis if motor nerves are affected


Autonomic Nerves Signs and Symptoms

  • Heat intolerance and altered sweating
  • Bowel, bladder or digestive problems
  • Changes in blood pressure, causing dizziness or lightheadedness

Peripheral neuropathy can affect one nerve (mononeuropathy), two or more nerves in different areas (multiple mononeuropathy) or many nerves (polyneuropathy).

Carpal tunnel syndrome is an example of mononeuropathy. Most people with peripheral neuropathy have polyneuropathy.


Avoiding a False Diagnosis


The diagnosis of peripheral neuropathy could be falsely attributed to the patient’s blood sugar management rather than to the side effects of the medication being used to treat the patient’s diabetes.


“Current British Society of Haematology guidelines recommend that vitamin B12 levels are checked only when there is clinical suspicion of deficiency,” explained Mulla. “However, peripheral neuropathy is irreversible and it may be too late once symptoms have developed.”

An unknowing doctor might even prescribe a higher dose of metformin to improve the patient’s blood sugar levels, not realizing that indeed a side effect of the drug itself is the culprit.


A misdiagnosis could lead to taking even more metformin.


“I’ve been hearing about this since about five years ago,” Dr. Caroline Messer, an endocrinologist and clinical assistant professor at Mount Sinai School of Medicine, “But there are no guidelines established for testing for it.”

Messer said the problem is that while some doctors are testing their patients’ vitamin B12 levels, many doctors are not because it hasn’t become an official part of standardized diabetes care.

“In my office, patients on metformin who are B12 deficient isn’t something we see often. It’s rare here, but this study says 10 percent of all patients taking metformin are deficient, and that’s not a small amount,” she said.


B12 Deficiency Symptoms



Vitamin B12 deficiency, also known as cobalamin deficiency, can be dangerous if it becomes severe.  A significant B12 deficiency can lead to severe and irreversible damage, especially to the brain and nervous system, so it’s important to catch it early.

Messer emphasizes that once the nerve damage is done, it cannot be fixed.

However, you can prevent further nerve damage after a B12 deficiency is identified through a basic blood test by taking supplemental B12.

Symptoms of B12 deficiency include diarrhea (which is also the most common side effect of metformin), constipation, exhaustion, loss of appetite, pale skin, inflamed red tongue, and bleeding gums.


Consequences of B12 Deficiency

The consequences of a B12 deficiency include permanent nerve damage, deteriorating brain function, memory loss, and temporary infertility in women.

In people without diabetes, B12 deficiency is considered common with as much as 15 percent of the American population deficient, according to the National Institutes of Health.

While it’s possible that metformin simply causes malabsorption of B12, Messer says there is no conclusive theory to explain why patients taking the drug become deficient.

And it isn’t just in patients who otherwise tolerate the drug well compared to patients who experience diarrhea and other gastric distress side effects.


Metformin and B12 Supplements


Messer says taking a supplement can treat the deficiency and prevent further nerve damage while still taking metformin as prescribed.


A normal B12 level is considered anywhere between 190 and 900 nanograms per milliliter (ng/mL), but Messer suggests treating any level below 300 ng/mL.

“Just have your levels checked every year if you take metformin,” she said. “For patients with levels over 300 mg/mL, taking a supplement isn’t necessary.”

Mulla added the same caution, concluding that patients shouldn’t stop taking metformin because of this research.

“Metformin remains the best treatment for type 2 diabetes. These findings should not discourage patients from taking it, but encourage doctors to monitor vitamin B12 levels more routinely, so any deficiency can quickly be treated.”


Sublingual B12 vs B12 Tablets

Although sublingual (dissolved under the tongue) B-12 and oral sprays are often promoted for better absorption than capsules or tablets, there does not appear to be reliable evidence for this, so it’s really just a matter of personal preference.

In fact, a clinical study, published in the British Journal of Clinical Pharmacology compared the same amount of B-12 given orally or sublingually found they were equally effective at correcting B-12 deficiency over a two-month period.

It should also be noted that unlike the vitamin B-12 in foods, the purified form of B-12 found in supplements, including tablets, requires stomach acid for absorption — a potential concern for people with low stomach acid (including many people over the age of 50) or those who take acid blockers such as Pepcid or Zantac, or proton pump inhibitors such as Prevacid, or Prilosec, who are at an increased risk for B-12 deficiency.


Recommended Vitamin B12 Supplements


EZ Melts Vitamin B12


PureControl Vitamin B12

B12 Sprays 

Mary Ruth’s Vegan, Non-GMO Liquid Spray B12



Final Thoughts

If your doctor has prescribed metformin for blood sugar control, show your physician this study and ask for a vitamin B12 blood test.

Seek medical care right away if you notice unusual tingling, weakness or pain in your hands or feet.

Early diagnosis and treatment offer the best chance for controlling your symptoms and preventing further damage to your peripheral nerves.

Are you taking metformin?  Please share your experience!

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