Background
Research indicates detrimental effects of stress on brain health and cognitive functioning, but population-based studies using comprehensive measures of cognitive decline is lacking. The present study examined the association of midlife perceived stress with cognitive decline from young adulthood to late midlife, controlling for early life circumstances, education and trait stress (neuroticism).

Methods
The sample consisted of 292 members of the Copenhagen Perinatal Cohort (1959–1961) with continued participation in two subsequent follow-up studies. Cognitive ability was assessed in young adulthood (mean age 27 years) and midlife (mean age 56 years) using the full Wechsler Adult Intelligence Scale (WAIS), and perceived stress was measured at midlife using the Perceived Stress Scale. The association of midlife perceived stress with decline in Verbal, Performance and Full-Scale IQ was assessed in multiple regression models based on Full Information Maximum Likelihood estimation.

Results
Over a mean retest interval of 29 years, average decline in IQ score was 2.42 (SD 7.98) in Verbal IQ and 8.87 (SD 9.37) in Performance IQ. Mean decline in Full-scale IQ was 5.63 (SD 7.48), with a retest correlation of 0.83. Controlling for parental socio-economic position, education and young adult IQ, higher perceived stress at midlife was significantly associated with greater decline in Verbal (β = − 0.012), Performance (β = − 0.025), and Full-scale IQ (β = − 0.021), all p < .05. Across IQ scales, additionally controlling for neuroticism in young adulthood and change in neuroticism had only minor effects on the association of midlife perceived stress with decline.

Conclusions
Despite very high retest correlations, decline was observed on all WAIS IQ scales. In fully adjusted models, higher midlife perceived stress was associated with greater decline on all scales, indicating a negative association of stress with cognitive ability. The association was strongest for Performance and Full-scale IQ, perhaps reflecting the greater decline on these IQ scales compared to Verbal IQ.