Effect of diabetes medications on the risk of developing dementia, mild cognitive impairment, or cognitive decline: A systematic review and meta-analysis

Background: Diabetes is a risk factor for dementia, but we do not know whether specific diabetes medications ameliorate this risk. Objective: To systematically review and meta-analyze such medication's effect on the risk of developing dementia, mild cognitive impairment (MCI), or cognitive decline. Methods: We searched three databases until 21 November 2023. We included randomized controlled trials (RCT), cohort, and case-control studies assessing association between antidiabetic medication and future dementia, MCI, or cognitive decline. We meta-analyzed studies separately for individual drug classes and their comparators (no medication, placebo, or another drug). We appraised study quality using the Newcastle-Ottawa Scale and Physiotherapy Evidence Database Scale. Results: 42 studies fulfilled inclusion criteria. Glucagon-like peptide-1 receptor agonists (GLP-1 RA) versus placebo reduced dementia risk by 53% in three RCTs (n = 15,820, RR = 0.47[0.25, 0.86]) and 27% in three case-control studies (n = 312,856, RR = 0.73[0.54, 0.99], I-2 = 96%). Repaglinide was superior to glibenclamide by 0.8 points on the Mini-Mental State Examination scale in another RCT. Meta-analysis of seven longitudinal studies showed glitazones (n = 1,081,519, RR = 0.78[0.76, 0.81], I-2 = 0%) were associated with reduced dementia risk. Metformin (n = 999,349, RR = 0.94[0.79, 1.13], I-2 = 98.4%), sulfonylureas (RR = 0.98[0.78, 1.22], I-2 = 83.3%), dipeptidyl peptidase-IV inhibitors (DPP-1V) (n = 192,802, RR = 0.86[0.65, 1.15], I-2 = 92.9%) and insulin (n = 571,274, RR = 1.09[0.95, 1.25], I-2 = 94.8%) were not. Most studies were observational and limited by confounding by indication. Conclusions: In people with diabetes, RCTs consistently showed GLP-RAs reduce future dementia risk. Glitazones consistently showed protective effects, without heterogeneity, suggesting potential generalizability of these results. Metformin, sulfonylureas, insulin, and DPP-1V studies had inconsistent findings. If information is available future studies should consider dosage, severity, and duration.