Mendelian randomization of smoking behavior on cognitive status among older Americans

BackgroundSmoking is a likely risk factor for dementia, and smoking behavior has a strong genetic component. In this study, we jointly test the associations between cumulative genetic risk for smoking, smoking behavior, and cognitive status using a Mendelian randomization framework. MethodsWe conducted a cross-sectional study using the 2010 wave of the Health and Retirement Study database. Individuals aged between 50 and 90 were included. Smoking status was self-reported. Polygenic scores (PGSs) were calculated by weighting participant genotype by published smoking genome-wide association estimates. Cognitive status (normal, impaired, dementia) was measured using multiple assessments. A Mendelian randomization framework was used to infer causal relationships between smoking behavior and cognitive status via genetic instruments. ResultsAmong European ancestry participants (N = 8,735), current smoking behavior was positively associated with cognitive impairment (OR = 1.62, 95% CI: 1.29, 2.01) relative to normal cognition. Using smoking PGS as an instrumental variable, a causal relationship was observed between current smoking and cognitive impairment (OR = 1.53, 95% CI: 1.07, 2.18). There were no associations between smoking PGS, smoking behaviors and cognitive status in the African ancestry study sample (N = 2,511). ConclusionsCurrent smoking is a modifiable risk factor which causes cognitive impairment. Promotion of smoking cessation is important for public health. Further studies on dose and duration of smoking behaviors on cognitive impairment are critically needed, as well as in research other ancestries.