Smoking Gun? Effect of smoking history on cognition in AD and MCI

Background Many lifestyle factors have been associated with lower rates of cognitive decline in AD and MCI patients, however the effect of tobacco smoking remains unclear. This study examined how longitudinal cognitive performance in AD and MCI patients varied for those with versus without smoking history. Method The study included all 126 patients from the Ontario Neurodegenerative Disease Research Initiative (ONDRI) AD/MCI cohort. The patients were divided into those with a history of cigarette smoking (n = 67) vs without (n = 59), defined as greater than two years of daily smoking. To measure longitudinal cognition, MoCA scores were taken three times with one year elapsing between assessments. Result Linear mixed effects models were performed, with MoCA score as the dependent variable. Time point, smoking history, sex, education, age, clinical diagnosis (AD vs MCI) and number of languages spoken were fixed effects and subject was a random effect. The presence of smoking history had a significant effect on MoCA score (χ2(1) = 4.5, p = 0.034), improving the average score by 1.37 points ± 0.66 (standard errors). A strong interaction was also found between smoking history and time point (χ2(1) = 8.2, p = 0.0042), as the positive effect of smoking history on MoCA score increased with time. No other significant interactions were found. Conclusion Our findings indicate that smoking history may improve longitudinal cognition in AD and MCI patients. It is unclear whether smoking history is simply a mediating variable for another protective factor, or whether these results arise from cigarette smoking itself affecting some stage of disease progression. Smoking has been consistently associated with a lower risk of developing Parkinson’s disease (PD), however the mechanism for such protection remains unclear. Further research into any association between smoking history and longitudinal cognition in AD and MCI might indicate whether a similar protective association is found in AD and MCI as exists in PD. However, it must be remembered that smoking is associated with many serious diseases, particularly lung cancer, and remains one of the biggest causes of preventable death worldwide.