Background Although being employed during midlife is positively associated with cognitive function in later life, little is known with respect to cumulative trajectories or durations of time spent in different kinds of work.

Methods We investigated the relationships between employment trajectory from ages 31 years to 50 years and cognitive skills at ages 50–78 years among 2521 adults in the US Panel Study of Income Dynamics from 1968 to 2016. Sequence analysis was used to identify prototypical employment trajectories, capturing employment status and high versus lower job skill level at each year of age from 31 years to 50 years. Adjusted and weighted logistic regression was used to estimate relationships between employment trajectory and performance on each of four cognitive tests representing numerical reasoning, verbal reasoning, health literacy and financial literacy. Dose–response relationships between the duration of high-skill employment and cognitive skills were examined.

Results Seven prototypical employment trajectories were identified, the most common being consistently lower skill employment (44%; 1105/2521). Consistently high-skill and fluctuating skill trajectories were associated with high numerical reasoning scores (OR=1.54, 95% CI 0.99 to 2.40; OR=2.52, 95% CI 1.39 to 4.58, respectively), compared with consistently lower skill employment. There was a dose–response relationship between duration of high-skill employment and numerical reasoning (OR=1.17; 95% CI 1.06 to 1.28), plateauing after approximately 4 years of high-skill employment.

Conclusions Sequence analysis of exposure trajectories is a novel method for life course epidemiology that accounts for exposure timing, duration and ordering. Our results using this method indicate that the duration may be more important than the timing of high-skill midlife employment for later-life numerical reasoning skills.