Objective To evaluate the association of different obesity phenotypes and their components with the risk of cognitive impairment in older Chinese adults, and to assess the association between obesity and cognitive impairment in different cognition-related genetic backgrounds.

Methods A cross-sectional study based on the West China Health and Aging Cohort was conducted. Logistic regression was applied to estimate the association of obesity phenotypes and components with cognitive impairment in older Chinese adults stratified by APOE gene and polygenic risk scores.

Results A total of 7316 participants were enrolled, of whom 1820 had cognitive impairment. Weight gains were associated with a reduced risk of cognitive impairment (odds ratio OR = 0.96, 95% CI, 0.95-0.97). Being overweight with a normal waist-to-hip ratio was a protective factor for cognition (OR = 0.74, 95% CI, 0.61-0.90), whereas the coexistence of elevated waist-to-hip ratio and overweight did not increase the risk of cognitive impairment. Sarcopenia was associated with an elevated risk of cognitive impairment. This association was found in both overweight (OR = 2.03, 95% CI, 1.71-2.41) and non-overweight older adults (OR = 1.86, 95% CI, 1.58-2.20), and was significant across all polygenic risk score strata.

Conclusion Increasing body mass may serve as a key protective factor against cognitive decline in older adults. Having sarcopenia and obesity is associated with an elevated risk of cognitive impairment, independent of genetic susceptibility.