Association between cumulative smoking exposure and cognitive decline in non-demented older adults: NEDICES study

Whether cumulative smoking exposure is associated with cognitive decline among older adults remains unresolved. To address this question, we used data from the Neurological Disorders in Central Spain (NEDICES) cohort study, in which 2624 older adults were evaluated at two-time points separated by three years. A 37-item version of the Mini-Mental State Examination (MMSE-37) was administered at two visits to assess cognitive change. Regarding smoking exposure, we calculated an individual baseline score based on pack-years (i.e., packs of cigarettes smoked per day multiplied by years of smoking) in current and former smokers. Thus, smoking exposure was categorized into tertiles (low: < 19.0, medium: 19.0-47.0, and high: > 47.0). We used multivariable generalized estimating equation models to assess associations between pack-years and smoking status with 37-MMSE total score change from baseline to follow-up. The MMSE-37 total score had a decline of 1.05 points (confidence interval [CI] 95% 0.62 to 1.48) in the lower tertile of pack-years, 1.16 (CI 95% 0.70 to 1.62) in the middle tertile and 1.17 (CI 95% 0.70 to 1.65) in the higher tertile compared to never smokers, after adjusting for several demographic and clinical variables. The same occurred with smoking status, i.e., a decline of 1.33 (CI 95% 0.87 to 1.79) in current smokers and 1.01 (CI 95% 0.63 to 1.40) in former smokers. Our study provides evidence of the cumulative effect of smoking on cognition in older adults. Using a prospective population-based design, we demonstrated that cumulative smoking exposure was associated with cognitive decline in non-demented older adults. More population-based evidence is required to elucidate this association in older adults without dementia.