Vitamin B12 levels, often depleted due to
metformin-induced malabsorption, should be monitored on a yearly basis in
diabetes receiving long-term metformin therapy,
Endocrine Today Editorial Board member David S.H. Bell, MD,
suggested in a case report published in the Southern Medical
A more cost-effective alternative method to avoid
vitamin B12 deficiency may be an annual vitamin B12 injection to provide more
than the annual vitamin B12 requirements for patients on chronic metformin
therapy, said Bell, of Southside Endocrinology and clinical professor of
medicine at the University of Alabama School of Medicine, Birmingham.
Vitamin B12 malabsorption is a chronic complication of
metformin therapy and can present with irreversible neuronal damage.
“Many people are unaware of metformin-induced
malabsorption of vitamin B12 and that is a potential problem,” he told
His recommendation comes after a case report of a
69-year-old white man with well-controlled type 2 diabetes (HbA1c, 6%) for six
years. The patient developed numbness in the feet, but did not report the
symptom to his physician. Several months later, a routine complete blood count
showed a hematocrit drop from 34% to 24% despite no change in mean corpuscular
volume. The patient also had a “very low” vitamin B12 level and was
started on vitamin B12 therapy.
After vitamin B12 therapy, the patient’s hematocrit
level returned to 24% but the numbness persisted. On physical examination, the
patient had bilateral loss of pinprick and vibration sense above the ankle
bilaterally and present, brisk ankle jerks.
Laboratory testing was negative for malabsorption and
celiac disease, and antiparietal antibody titer and serum gastrin levels were
normal, which ruled out pernicious anemia. One year later, the patient’s
neuropathic symptoms had not improved or worsened.
“This patient developed peripheral neuropathy after
only three years of therapy with metformin, presumably because he had
thalassemia minor and increased red cell turnover, which, in conjunction with
metformin-induced vitamin B12 malabsorption, rapidly depleted his vitamin B12
stores,” Bell wrote in the report.
This case is exceptional, he added, because “it shows a rapid development of neuropathy due to vitamin B 12 deficiency. To my knowledge, this is also the first case described of metformin-induced neuropathy due to metformin-induced vitamin B12 absorption,” he wrote.
Metformin-induced malabsorption of vitamin B12 is a
complication that affects about 30% of patients with diabetes who are
administered the drug. Despite its common occurrence, vitamin B12 deficiency is
often unrecognized and untreated.
Further, misdiagnosis is common due to the resemblance
of vitamin B12 deficiency to diabetic neuropathy, Bell said.
“The two are very similar,” he said.
“During a physical examination, though, if the reflexes are maintained in
spite of sensory loss, this is a red flag that it may be vitamin B12
Based on the above report and previous data, Bell said
patients with diabetes who take long-term metformin treatment should have their
vitamin B12 levels monitored annually. Another option would be an annual
1,000-mcg injection of vitamin B12. He said he checks vitamin B12 levels during
the annual physical examination for all patients.
It is estimated that the body’s store of vitamin
B12 lasts 12 to 15 years before becoming deficient.
“One annual vitamin B12 shot may be enough for most
patients; it takes a long time to deplete vitamin B12,” Bell said.
Metformin use has reached a stage at which Bell said he
expects to see a significant rise in cases of vitamin B12 deficiency.
“We’ve had metformin since 1995, and I think
that as time goes on, it could snowball. … It has the potential to be a
significant problem,” he said. – by Matthew Brannon
Bell SH. Southern Medical Journal.
the Journals summaries>>
EndocrineToday.com on Twitter.