Association of blood cotinine level with cognitive and physical performance in non-smoking older adults

Background Studies show that active smoking may be associated with cognitive decline. However, the consequence of secondhand smoke on cognitive and physical performance remains unclear. The purpose of this study was to assess the association of secondhand smoke with cognitive performance and physical function using a population-based sample.

Data of 2,542 non-smoking participants from the 1999-2002 National Health and Nutrition Examination Survey were analyzed. Secondhand smoke exposure level was estimated using blood cotinine concentrations. Cognitive performance was assessed with the Digit Symbol Substitution Test and self-reported confusion/memory problems. Physical performance was analyzed using visual gait speed (m/s) and self-reported physical function. Multivariate linear and logistic regression models were used to assess the association.

In never smokers, cognitive performance score decreased by 2.03 points (95% confidence interval (CI): -3.00, -1.05) per one unit increase in log-transformed blood cotinine level. After adjusting for potential confounders, including diabetes, hypertension, body mass index, alcohol, and blood lead level, change in cognitive performance score was still statistically significant (-1.17 95% CI: -2.32, -0.02). Similar trends were observed in former smokers. Gait speed decreased by 0.02m/s for one unit increase in log-transformed blood cotinine level. This was evident in both never and former smokers. The relationship remained significant after adjusting for potential confounders in former smokers.

Our study suggests that secondhand smoke may contribute to cognitive decline in never and former smokers. Considering the cross-sectional design and the limitations of this study, the relationship warrants further assessment.