Do we need to measure vitamin B12 and magnesium in morbidly obese patients with type 2 diabetes mellitus?

Objective: We aimed to investigate the prevalence of B12 deficiency in metformin-treated, morbidly obese, type 2 diabetes mellitus (T2DM) patients, compared to morbidly obese controls, as well as to evaluate the magnesium status. Design: Retrospective cross-sectional analysis of plasma vitamin B12, plasma magnesium, glucometabolic status and clinical measurements in all consecutive morbidly obese patients was conducted during 1 year. Setting: Outpatient Clinic of Obesity Care. Subjects: One hundred forty-seven patients were evaluated: 107 morbidly obese controls and 40 metformin-treated, morbidly obese patients with T2DM. Main outcome measures: Circulating plasma concentrations of vitamin B12 (cobalamin), magnesium, clinical measurements and metformin medication. Results: There were differences between the two groups regarding age, sagittal diameter, glucose parameters and magnesium concentrations. Longer diabetes duration was associated with lower magnesium. Metformin-treated T2DM patients had lower magnesium (0.76 +/- 0.07 mmol/L) than controls (0.82 +/- 0.07 mmol/L). A subgroup analysis of 26 non-metformin-treated T2DM patients showed a normal magnesium concentration compared to controls, that is, 0.81 +/- 0.06 mmol/L. We found no statistical difference in B12 concentrations between the two groups. Conclusion: To fully benefit from metformin medication, routine testing of B12 as well as magnesium in metformin-treated, morbidly obese patients should be performed, with consideration of substitution to avoid low levels.