Associations of metabolic syndrome with risks of dementia and cognitive impairment: A systematic review and meta-analysis

Background Previous studies have linked metabolic syndrome (MetS) to dementia risk. Objective We conducted a systematic review and meta-analysis to assess the association between MetS and dementia as well as cognitive impairment, with additional focus on individual MetS components. Methods We systematically searched the PubMed, Embase, and Cochrane Library databases from inception through July 2024. We used random-effects models to calculate relative risks (RRs) and odds ratios (ORs) with 95% confidence intervals (CIs). Publication bias was evaluated using the Egger's test, while potential sources of heterogeneity were investigated through meta-regression, subgroup, and sensitivity analyses. Results Our analysis included 21 studies with a total of 411,810 participants. MetS was associated with increased risks of all-cause dementia (RR = 1.33, 95% CI = 1.03–1.71, I² = 85.8%) and vascular dementia (RR = 2.07, 95% CI = 1.32–3.24, I² = 10.1%), but not Alzheimer's disease (RR = 1.10, 95% CI = 0.64–1.91, I² = 81.8%). Regarding cognitive impairment, longitudinal studies showed an increased risk (OR = 1.38, 95% CI = 1.24–1.53, I² = 3.3%), with similar findings in cross-sectional studies (OR = 1.65, 95% CI = 1.19–2.28, I² = 85.3%). Conclusions This study found that MetS is significantly associated with increased risks of dementia and cognitive impairment, with each component potentially being a modifiable factor. These findings may help guide clinicians in recommending lifestyle interventions to prevent cognitive decline and promote brain health.