Sleep duration in midlife and later life in relation to cognition

To evaluate associations between sleep duration at midlife and later life and change in sleep duration over time and cognition in older women.

Participants reported sleep duration in 1986 and 2000, and a subgroup of older participants began cognitive testing in 1995 to 2001; follow-up testing was conducted three times, at 2-year intervals.

Prospective Nurses' Health Study cohort.

Female nurses aged 70 and older free of stroke and depression at the initial cognitive assessment (N = 15,385).

Validated, telephone-based cognitive battery to measure cognitive function; four repeated assessments over 6 years were averaged to estimate overall cognition at older ages, and trajectories of cognitive change were evaluated over follow up.

Extreme sleep durations in later life were associated with worse average cognition (P < .001 for the quadratic term for a global score averaging all six cognitive tests). For example, women sleeping 5 h/d or less had worse global cognition than those sleeping 7 h/d, as did women sleeping 9 h/d or more; differences were equivalent to nearly 2 additional years of age. Associations were similar, although slightly attenuated, for sleep duration in midlife. Women whose sleep duration changed by 2 h/d or more over time had worse cognition than women with no change in sleep duration (e.g., for the global score, P < .001 for the quadratic term). Sleep duration was not associated with trajectories of cognitive function over 6 years, which might be attributable to short follow-up for detecting cognitive decline.

Extreme sleep durations at midlife and later life and extreme changes in sleep duration over time appear to be associated with poor cognition in older women.