Background and aims: The extent and timing of cognitive decline is highly debated in the literature as most longitudinal studies are flawed by few participants, short follow-up and loss to follow-up due to mortality. In addition, limited consistent evidence concerning the influence of education on the rate of cognitive decline exists; although education is strongly correlated with cognitive performance at all adult ages. The aims of our study were to explore general trends and individual differences in age-related cognitive changes from early adulthood to midlife and to investigate associations between education and cognitive changes.
Methods: Data from the Lifestyle and Cognition follow-up study 2015 (LiKO-15) were used, including 1543 Danish men born in 1950–61, draft board (baseline) examined in 1968–89 and re-examined in a 2015–17 follow-up. Participants completed the 78-item intelligence test used by the Danish conscription authorities, Børge Priens Prøve (BPP), at baseline (mean age=20 years) and at follow-up (mean age=61 years). The difference in BPP test scores was used as the outcome measure of cognitive changes. The influence of self-reported years of education from follow-up on cognitive changes was analyzed in multiple linear regression models adjusted for follow-up age and further adjusted for baseline BPP scores. In addition, a model including an interaction between years of education and baseline BPP scores was analyzed.
Results: The mean change in BPP test scores was -2.94 (SD 5.60) and a retest correlation of 0.81 between the baseline and follow-up BPP scores was observed. In spite of the substantial retest correlations, individual differences in BPP change scores were also substantial. More years of education was associated with larger mean decline in BPP test scores, but the association was reversed when adjusting for baseline BPP scores. Moreover, significant interactions indicated that years of education was positively associated with cognitive changes in men with low and medium baseline scores but not in men with high baseline scores.
Conclusions: The mean cognitive decline is relatively modest from young adulthood to late midlife, but individual differences are substantial. Higher educational attainment was associated with less cognitive decline in men with low or medium baseline cognitive ability, but not in men with high baseline cognitive ability.
