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.