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.