Smoking increases the risk of delirium for older inpatients: A prospective population-based study

Objectives: To investigate the association between smoking in the older population and the risk of inpatient delirium, which is common and has adverse consequences. Method: Participants (N= 3754) were insurants aged ≥ 55 years of the largest German statutory health insurance company, who enrolled in a 6-year prospective population-based study. Baseline smoking, adjusted for age, sex, depressive symptoms, cognitive impairment and alcohol consumption, was analyzed as risk factor of inpatient delirium. Results are presented as hazard ratios (HRs) and 95% confidence intervals (95% CIs). Results: Three-hundred seventy-three (10.0%) participants were smokers at baseline, 865 (23.0%) were quitters and 2516 (67.0%) were lifelong abstainers. Mean pack-years of smokers and quitters were 23.8 (S.D.=22.4). Sixty-one (1.6%) received a diagnosis of inpatient delirium. Smokers had an increased risk of delirium compared to abstainers in the fully adjusted model (HR=2.87, 95% CI 1.24-6.66). Quitters and abstainers did not differ (HR=0.79, 95% CI 0.37-1.72). Comparing smokers and quitters, current smoking status (HR=3.22, 95% CI 1.20-8.62) but not pack-years [residual χ²(1)=0.25, P=874] were associated with inpatient delirium. Conclusion: Only current smoking but not being a quitter and the lifetime amount smoked were associated with inpatient delirium, indicating that acute nicotine withdrawal may represent a relevant pathogenic mechanism.