Uraiporn Booranasuksakul, Zhongyang Guan, Leticia Radin Pereira, Kostas Tsintzas, Ian Macdonald, Ellise Stirling, Sana Farzam, Lorenzo M Donini, Alexandra M Johnstone, Marc Sim, Blossom Stephan, Mario Siervo
Sarcopenia and obesity, characterised respectively by reduced muscle mass and function and increased adiposity, may co-occur as sarcopenic obesity (SO). This systematic review summarises cohort evidence linking these body composition phenotypes to dementia risk. MEDLINE, EMBASE, Cochrane Database and PsycINFO were searched from inception to February 2026. Outcomes included incident all-cause dementia (ACD) and subtypes. Pooled hazard ratios were calculated for each phenotype using random-effects models. Fourteen publications were included for sarcopenia, 72 for obesity, and four for SO. Late-life obesity (≥65 years) was protective for ACD (HR 0.83, 95% CI 0.76-0.89), whereas mid-life obesity (<65 years) modestly increased risk (HR 1.09, 95% CI 1.01-1.16). Sarcopenia was associated with increased risk (HR 1.42, 95% CI 1.26-1.58). SO showed no significant association (HR 1.43, 95% CI 0.87-1.99). These findings highlight age-dependent effects of obesity and an elevated dementia risk with sarcopenia; the predictive role of SO requires further research.