The aim of this PhD thesis is to examine the association between sleep characteristics (duration and difficulties) and cognitive function in late mid-life and old age – especially around the retirement transition. It comprises of four cohort studies: the Finnish Retirement and Aging Study (n=289), the Cardiovascular Risk in Young Finns Study (n=1908), the Turku Senior Health Clinic Study (n=758), and the Whitehall II Study (n=2980). Sleep characteristics were measured through selfreports and accelerometer readings, and cognitive function was measured using paper-and-pencil and computer-based tests across multiple cognitive domains. Sleep characteristics and cognitive function were examined cross-sectionally as well as longitudinally, using repeated measurements before and after retirement.

Long sleep duration in late mid-life and old age was associated with multiple cognitive domains, including poorer learning and memory, complex attention, and executive function. Difficulties staying asleep and nonrestorative sleep were associated with executive function among the participants who were still actively working. Sleeping more than usual the night prior to cognitive testing was associated with poorer information processing. Cognitive function, especially learning and memory, temporarily improved during retirement transition independently from changes in sleep characteristics. In a longer follow up around the retirement transition, increasing and decreasing sleep difficulties were associated with a pronounced decline in cognitive function during and after the retirement transition.

In conclusion, long sleep duration and sleep difficulties were associated with poorer cognitive function before and after retirement. Cognitive function temporarily improved during the retirement transition, and future research should focus on finding the cause behind this improvement in order to promote improved cognitive health in working life.