Associations of Metformin Use History With Delirium and Mortality in Patients With Type 2 Diabetes Mellitus: A Retrospective Cohort Study.

Background: Higher body mass index (BMI) generally increases susceptibility to certain diseases. However, previous studies have shown that metformin, a medication for type 2 diabetes mellitus (T2DM), can improve various outcomes, including survival in obese patients. This indicates that the effectiveness of metformin on certain outcomes is more pronounced in those with a higher BMI. It remains unclear if the effects of metformin on delirium risk differ according to BMI.

Methods: This study analyzed a subset of 506 T2DM subjects from the cohort used in our previous study. We compared delirium cases identified during hospitalization and survival curves among T2DM subjects with and without a history of metformin use, stratified by BMI. Furthermore, we investigated the influence of metformin use history and various other factors on cases of delirium identified during hospitalization and 3-year mortality among T2DM subjects in different BMI groups.

Results: Metformin use history was associated with fewer cases of delirium (odds ratio = 0.422, 95% confidence interval [CI] = 0.217-0.820, P = 0.011) and lower 3-year mortality (hazard ratio = 0.564, 95% CI = 0.342-0.931, P = 0.025) among the BMI ≥30 group. On the other hand, the associations between metformin use history and fewer cases of delirium (odds ratio = 0.606, 95% CI = 0.320-1.150, P = 0.125) and lower 3-year mortality (hazard ratio = 0.754, 95% CI = 0.447-1.270, P = 0.288) among the BMI <30 group were relatively small and nonsignificant.

Conclusions: Metformin use history was associated with a lower risk of delirium and mortality in the T2DM obesity group.