Metformin helps to 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, according to the National Institutes of Health.
“Metformin is the most commonly used drug to treat type 2 diabetes,
so many millions of people are taking it, usually for a prolonged
period (many years),” said senior study author Dr. Jill P Crandall
of Albert Einstein College of Medicine in New York City, by email.
“Smaller numbers of people take metformin for prevention of diabetes
or treatment of polycystic ovary syndrome,” Crandall told Reuters
The researchers 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
The 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 than did not include
medication. For the new analysis only those taking placebo or
metformin were considered, and about 50 participants were excluded
after having weight-loss surgery, which would affect their diabetes
During follow-up, the participants provided blood samples at the
five- and 13-year points.
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, as reported in the Journal of Clinical Endocrinology
Vitamin B12 deficiency may lead to nerve damage which can be severe
and may be irreversible, Crandall said.
“Severe and prolonged B12 deficiency has also been linked to
impaired cognition and dementia,” she said. “It can also cause
anemia (low red blood cell count) - fortunately, this condition is
reversible with treatment.”
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More people in the metformin group were also anemic at year five
than in the placebo group.
There are more than three million cases of vitamin B12 deficiency
each year in the U.S., which can be caused by diet or certain
medical conditions. Symptoms include fatigue, and numbness or
Humans do not make vitamin B12 and need to consume it from animal
sources or supplements. Vegetarians may get enough from eating eggs
and dairy products, but vegans need to rely on supplements or
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 conclude.
“The FDA and organizations such as the American Diabetes Association
do not have any formal recommendations for B12 monitoring for people
taking metformin,” Crandall said. “That said, our study (and others)
suggests that a small but significant number of people may develop
“People who are taking metformin should ask their doctor about
measuring their B12 level,” she said.
Restoring healthy B12 levels is easy to accomplish with pills or
monthly injections, she added.
“The risk of B12 deficiency should not be considered a reason to
avoid taking metformin,” Crandall said.
SOURCE: http://bit.ly/1SWRxed Journal of Clinical Endocrinology and
Metabolism, online February 22, 2016.
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