The findings of a study confirming a link between metformin and vitamin B12 deficiency serve as a timely reminder for clinicians to test their patients on a regular basis, an expert says.

The comment comes after a study from the US Diabetes Prevention Program Research Group found that people taking metformin were more likely to be vitamin B12 deficient.

After controlling for factors that might affect B12 levels the study involving more than 2000 participants from 27 centres in the US found a 13% increased risk of vitamin B12 deficiency per year of metformin use.

According to the authors of the study published in the Journal of Clinical Endocrinology and Metabolism there was some debate about the clinical significance of biochemical vitamin B12 deficiency versus true tissue deficiency.

However homocysteine levels were increased in those with borderline-low vitamin B12 levels, a finding that they said was indicative of the presence of vitamin B12 deficiency at the tissue level.

Vitamin B12 deficiency linked to metformin therapy was generally well recognised Professor Stephen Twigg, who is Head of Endocrinology at Royal Prince Alfred Hospital in Sydney told the limbic.

“Metformin Product Information recommends periodic screening in especially high-risk individuals..but clinical practice guidelines often don’t recognise the need for ongoing monitoring of vitamin B12 levels,” he said.

Replacing vitamin B-12 in patients who were taking metformin was also an issue, said Professor Twigg who tests all of his patients for deficiency at their annual complications screening appointment.

“In general, I continue the metformin and use parenteral B-12 as metformin probably lowers B-12 absorption and so oral replacement may not be as efficient,” he said.