Long sleep duration is associated with lower cognitive function among middle-age adults - the Doetinchem Cohort Study.

OBJECTIVES: In older adults, both short and long sleep duration are associated with lower cognitive function, suggesting an inverted U-shaped association between sleep duration and cognitive outcomes. This study examined whether sleep duration is associated with (changes in) cognitive function in a middle-aged population.

METHODS: In the Doetinchem Cohort Study, the cognitive function of 2970 men and women aged 41-75 years at baseline (1995-2007) was examined 2-3 times, with 5-year time intervals. Global cognitive function and the domains memory, information processing speed, and cognitive flexibility were assessed. In multivariable linear regression models, (change in) self-reported sleep duration was studied in association with the level and change in cognitive function. In a subsample of the population (n = 2587), the association of sleep duration and feeling rested with cognitive function was studied.

RESULTS: Sleep duration of 9 h and more was statistically significantly associated with lower global cognitive function (p < 0.01), memory (p = 0.02), and flexibility (p = 0.03), compared to a sleep duration of 7 or 8 h. Among adults feeling frequently not well rested, both short and long sleep duration were associated with a lower speed of cognitive function. An inverted U-shaped association between sleep duration and cognitive function was observed for speed, flexibility, and global cognitive function. Sleep duration was not associated with change in cognitive function.

CONCLUSIONS: Middle-age adults with long sleep duration had a lower cognitive function.