Why Some Diabetes Patients Taking Metformin Need More Vitamin B12

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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 from research conducted by two hospitals in the United Kingdom 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 B12 is important
Vitamin B12 plays a critical role in the development and function of brain and nerve function.
The most significant concern is that even a patient who is managing their blood sugars at healthy levels could still experience severe and permanent nerve damage.
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.”
That 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.
“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, told Healthline. “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.