Evaluating GLP-1 receptor agonists versus metformin as first-line therapy for reducing dementia risk in type 2 diabetes

Discussion

This study represents the first and largest direct comparison of GLP-1 RAs and metformin in mitigating dementia risk among patients with T2DM. Historically, metformin has been the cornerstone of first-line therapy for T2DM due to its well-established efficacy in glycemic control and its potential neuroprotective effects.20–28 However, whether initiating GLP-1 RAs as first-line therapy could offer superior benefits in reducing diabetes-related dementia risk has remained unaddressed. The findings demonstrated that GLP-1 RAs significantly reduced the incidence of overall dementia compared with metformin (2.4% vs 4.8%; AHR, 0.90; 95% CI 0.85 to 0.95), with pronounced benefits observed in AD and other dementia subtypes. Notably, GLP-1 RAs also provided substantial reductions in all-cause mortality. These findings address a key knowledge gap by directly comparing the neuroprotective efficacy of GLP-1 RAs and metformin in dementia prevention. Given the increasing global burden of diabetes-related cognitive decline and the lack of head-to-head comparisons between GLP-1 RAs and metformin, our findings provide actionable insights for clinical decision-making and may inform future guidelines. Additionally, the study underscores the importance of tailoring therapeutic strategies to optimize both metabolic and neuroprotective outcomes in high-risk T2DM populations. Further randomized controlled trials (RCTs) are warranted to confirm these findings and evaluate the long-term cognitive benefits of GLP-1 RAs.

GLP-1 RAs demonstrate superior efficacy compared with metformin in reducing the risk of AD and other non-VaDs in patients with T2DM, as evidenced by our study and corroborated by other research. In our cohort, GLP-1 RA use was associated with a significant reduction in the risk of AD (AHR 0.88; 95% CI 0.83 to 0.94) and other non-VaDs (AHR 0.75; 95% CI 0.70 to 0.81) compared with metformin, underscoring their potential neuroprotective advantage. Similar findings have been reported in clinical trials and population-based studies. For instance, an RCT of liraglutide in patients with early AD demonstrated improvements in cognitive function and reductions in cerebral amyloid burden,30 aligning with the mechanisms identified in our study.31–33 Another large-scale observational study of Danish registries showed a lower incidence of dementia among GLP-1 RA users compared with other antidiabetic therapies, consistent with our results.34 Mechanistically, GLP-1 RAs reduce neuroinflammation, enhance synaptic plasticity, and modulate amyloid-beta and tau pathologies—features that are central to AD’s neurodegenerative process.15 31–33 In contrast to metformin’s predominantly systemic metabolic effects, GLP-1 RAs exert direct neuroprotective actions, enhancing blood-brain barrier integrity and promoting neurotrophic signaling.35–37 These findings collectively highlight the promise of GLP-1 RAs in mitigating the burden of neurodegenerative dementias in T2DM, emphasizing their potential as a preferential therapeutic option over metformin for this high-risk population.

The differential effects of GLP-1 RAs and metformin on overall dementia and VaD highlight the complexity of their mechanisms and the pathophysiology of these conditions. Both medications demonstrate neuroprotective properties, such as reducing neuroinflammation and oxidative stress, improving insulin sensitivity, and enhancing cerebrovascular health, which likely contribute to their benefits in overall dementia.11–17 24–28 However, the multifactorial nature of VaD,38 driven by cerebrovascular damage such as small vessel disease and white matter lesions, poses significant challenges for pharmacological interventions targeting metabolic or neurodegenerative pathways.3 5 6 Interestingly, a modest but significant reduction in VaD risk was observed exclusively in female patients treated with GLP-1 RAs (aHR 0.88; 95% CI 0.79 to 0.99), whereas no significant differences were noted in the overall population (figure 2B). This finding may be influenced by estrogen’s vascular and neuroprotective effects,39 which could enhance the benefits of GLP-1 RAs or metformin in postmenopausal women.8 Sex-specific metabolic and inflammatory differences in diabetes further underscore the potential role of biological variables in modulating treatment efficacy.40 The limited impact of GLP-1 RAs and metformin on VaD may also reflect study design limitations, including potential misclassification, underdiagnosis of VaD, and insufficient statistical power due to its relatively low incidence. These findings emphasize the need for personalized therapeutic strategies and future research to explore sex-specific factors, longer follow-up durations, and synergistic effects of combined therapies to optimize dementia prevention in T2DM.

GLP-1 RAs demonstrate substantial promise in reducing the risk of T2DM-related dementia, particularly AD and other non-VaDs, through their broad neuroprotective mechanisms (figure 2 A-D). Unlike metformin, whose benefits primarily derive from systemic metabolic effects such as improved insulin sensitivity and reduced oxidative stress,24–28 GLP-1 RAs exert direct central nervous system effects by crossing the blood-brain barrier.35–37 These mechanisms include attenuating neuroinflammation, reducing oxidative stress, promoting the release of neurotrophic factors critical for neuronal survival and synaptic plasticity, and enhancing cerebral glucose metabolism—a key function often impaired in neurodegenerative diseases like Alzheimer’s.11–17 35–37 In addition, GLP-1 RAs uniquely target the pathological hallmarks of AD, including reducing beta-amyloid deposition and tau protein hyperphosphorylation,15 31–33 while restoring blood-brain barrier integrity to prevent neurotoxic insults. These findings are supported by comparative studies, which have demonstrated cognitive improvements and reduced neurodegenerative burden in patients treated with GLP-1 RAs such as liraglutide and semaglutide.7 8 18 19 Our study corroborates these results, showing significant reductions in AD risk associated with GLP-1 RAs, highlighting their potential superiority over metformin in addressing the multifaceted pathophysiology of neurodegenerative dementias. Given the severe societal, familial, and economic burden of diabetes-related dementia,2 3 these findings raise important considerations about the role of GLP-1 RAs as first-line therapies in T2DM management. While further long-term studies are warranted to validate these results, integrating GLP-1 RAs as primary therapeutic agents may represent a paradigm shift in preventing the cognitive complications of diabetes.

This study represents the largest and most comprehensive evaluation of GLP-1 RAs compared with metformin as first-line antidiabetic therapies in mitigating the risk of T2DM-related dementia, with a specific emphasis on AD and other non-VaDs. Leveraging the global federated health research network, encompassing deidentified data from over 98 healthcare organizations worldwide, this analysis ensures broad generalizability and robust methodological rigor. Advanced techniques, including PSM and sensitivity analyses, minimized confounding and validated the robustness of the findings. GLP-1 RAs demonstrated significant reductions in AD risk (AHR 0.88; 95% CI 0.83 to 0.94) and other non-VaDs (AHR 0.75; 95% CI 0.70 to 0.81), consistent with prior research highlighting their neuroprotective mechanisms, such as reducing beta-amyloid accumulation, alleviating oxidative stress, and enhancing cerebral glucose metabolism.7 8 18 19 By providing direct comparative evidence, this study addresses a critical gap in the literature and underscores the potential of GLP-1 RAs as a superior therapeutic option for preventing T2DM-related cognitive decline. These findings offer actionable insights for clinicians and policymakers, emphasizing the importance of integrating neuroprotective strategies into diabetes management to address the growing burden of dementia.

This study has several limitations that should be acknowledged. First, as a retrospective cohort study using real-world data, the potential for residual confounding remains, despite rigorous PSM and sensitivity analyses. Second, the reliance on deidentified EHRs introduces variability in diagnostic coding, which may lead to misclassification of dementia subtypes or underreporting of outcomes, particularly VaD. Third, the exclusion of patients with prior exposure to both GLP-1 RAs and metformin may limit the generalizability to individuals with mixed treatment histories. Fourth, the follow-up period, while sufficient for observing dementia outcomes, may not fully capture long-term cognitive effects, especially given the progressive nature of neurodegenerative diseases like Alzheimer’s. Additionally, the absence of direct cognitive performance measurements or biomarkers (eg, amyloid or tau) limits mechanistic insights into the observed benefits of GLP-1 RAs. Lastly, although the study population was diverse, it may not represent certain high-risk groups, such as those with advanced diabetes complications or significant comorbidities. Despite these limitations, the findings remain robust, as the lower mortality in the GLP-1 RA group—paradoxically reducing dementia risk due to longer survival—suggests that the study may have underestimated the true neuroprotective effects of GLP-1 RAs compared with metformin. This underscores the potential superiority of GLP-1 RAs and highlights the need for further randomized controlled trials with extended follow-up, standardized diagnostics, and neuroimaging to validate these findings.

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