Long term use of metformin, the most common drug used to prevent and treat type 2 diabetes, may increase the risk of vitamin B12 deficiency and anemia, according to a new analysis of long-term data.
Metformin helps control the amount of sugar, or glucose, in the blood by reducing how much glucose is absorbed from food and produced by the liver and by increasing the body’s response to the hormone insulin.
The researchers, from the Albert Einstein College of Medicine in New York City, used data from the Diabetes Prevention Program and the Diabetes Prevention Program Outcomes Study, which followed participants at high risk for type 2 diabetes for more than 10 years.
The original study began with more than 3,000 people age 25 years and older with high blood sugar. The participants were randomly assigned to receive either 850 milligrams of metformin twice daily, placebo medication or an intensive lifestyle program (weight loss plus exercise) than did not include medication. For the new analysis only those taking placebo or metformin were considered.
During follow-up, the participants provided blood samples at the five- and 13-year points.
B12 deficiency and anemia more common among metformin users
Using these blood samples, the researchers found that at year five, average B12 levels were lower in the metformin group than the placebo group, and B12 deficiency was more common, affecting 4 percent of those on metformin compared to 2 percent of those not taking the drug.
Borderline low B12 levels affected almost 20 percent of those on metformin and 10 percent of those taking placebo.
Average vitamin B12 levels were higher by year 13 than in year five, but B12 deficiency was also more common in both the metformin and placebo groups.
More people in the metformin group were also anemic at year five than in the placebo group.
What does B12 do in the body?
Vitamin B12 helps keep the body's nerve and blood cells healthy and is needed to make DNA, the genetic material in all cells. Vitamin B12 deficiency can cause anemia and may lead to nerve damage, which can be severe and may be irreversible.
Severe and prolonged B12 deficiency has also been linked to impaired cognition and dementia.
Humans do not make vitamin B12 and need to consume it from animal foods or supplements. Vegetarians may get enough from eating eggs and dairy products, but vegans need to rely on supplements or fortified foods.
Doctors who prescribe metformin to patients long-term for type 2 diabetes, gestational diabetes, polycystic ovarian syndrome or other indications should consider routine measurement of vitamin B12 levels, the authors concluded.
Source: Journal of Clinical Endocrinology and Metabolism, online February 22, 2016.
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