Early to Midlife Smoking Trajectories and Cognitive Function in Middle-Aged US Adults: the CARDIA Study

Background: Smoking starts in early adulthood and persists throughout the life course, but the association between these trajectories and midlife cognition remains unclear.

Objective: Determine the association between early to midlife smoking trajectories and midlife cognition.

Design: Prospective cohort study.

Participants: Participants were 3364 adults (mean age = 50.1 ± 3.6, 56% female, 46% Black) from the Coronary Artery Risk Development in Young Adults (CARDIA) study: 1638 ever smokers and 1726 never smokers.

Main measures: Smoking trajectories were identified in latent class analysis among 1638 ever smokers using smoking measures every 2-5 years from baseline (age 18-30 in 1985-1986) through year 25 (2010-2011). Poor cognition was based on cognitive domain scores ≥ 1 SD below the mean on tests of processing speed (Digit Symbol Substitution Test), executive function (Stroop), and memory (Rey Auditory Verbal Learning Test) at year 25.

Results: Five smoking trajectories emerged over 25 years: quitters (19%), and minimal stable (40%), moderate stable (20%), heavy stable (15%), and heavy declining smokers (5%). Heavy stable smokers showed poor cognition on all 3 domains compared to never smoking (processing speed AOR = 2.22 95% CI 1.53-3.22; executive function AOR = 1.58 95% CI 1.05-2.36; memory AOR = 1.48 95% CI 1.05-2.10). Compared to never smoking, both heavy declining (AOR = 1.95 95% CI 1.06-3.68) and moderate stable smokers (AOR = 1.56 95% CI 1.11-2.19) exhibited slower processing speed, and heavy declining smokers additionally had poor executive function. For minimal stable smokers (processing speed AOR = 1.12 95% CI 0.85-1.51; executive function AOR = 0.97 95% CI 0.71-1.31; memory AOR = 1.21 95% CI 0.94-1.55) and quitters (processing speed AOR = 0.96 95% CI 0.63-1.48; executive function AOR = 0.98 95% CI 0.63-1.52; memory AOR = 0.97 95% CI 0.67-1.39), no association was observed.

Conclusions: The association between early to midlife smoking trajectories and midlife cognition was dose-dependent. Results underscore the cognitive health risk of moderate and heavy smoking and the potential benefits of quitting on cognition, even in midlife.