Atti AR, et al. - According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement, researchers performed a systematic review and a meta-analysis of clinical and population-based studies investigating how metabolic syndrome (MetS) influences the risk for incident dementia, Alzheimer disease (AD), and vascular dementia (VaD). Further, they assessed the involvement of MetS in progression to dementia in patients affected by mild cognitive impairment (MCI). Nine longitudinal studies (six studies enrolling cognitively well-functioning participants and three studies involving MCI patients) were included in this study. A follow-up for an average for 9.41 years was performed in the 18,313 participants aged older than 40 years with a mean prevalence of MetS of 22.7%. MetS showed no statistically significant pooled association with incident dementia and AD. Increased incidence of pure VaD and increased risk of progression from MCI to dementia MetS were noted in relation with MetS.