Nocturnal sleep duration and cognitive impairment in a population-based study of older adults.
We examined the association of sleep duration, snoring, and difficulty sleeping with cognitive function in a cohort of community-dwelling women. Women (n = 1844), aged 70 to 81 years at initial cognitive interview in 2000, are members of the Nurses' Health Study cohort. Women completed six tests of cognitive function encompassing general cognition, verbal memory, category fluency, and attention. We repeated the assessment 2 years later. We used linear regression models to obtain multivariate-adjusted mean differences in initial test performance, and in cognitive decline over time, across categories of sleep duration (< or =5,6,7,8,9+ hours/night), frequency of snoring (never, occasionally, regularly), and sleep difficulties (rarely/never, occasionally, regularly). In analyses of initial test performance, women sleeping < or =5 hours/night scored worse than women sleeping 7 hours/night (mean difference on global score combining all cognitive tests = 0.15 standard units, 95% CI: -0.28, -0.02). Women who regularly had difficulty falling or staying asleep scored 0.11 units lower on the global score (95% CI: -0.22, 0.01) compared with those who rarely had difficulty sleeping. These differences were equivalent to the mean differences in score observed between participants who were 4 to 5 years apart in age. We found no associations with snoring or with any of the sleep variables and cognitive decline over 2 years. Associations between sleep patterns and initial cognitive function may be clinically relevant given that diminished cognition is a risk factor for dementia. However, the lack of an association with prospective cognitive decline warrants further investigation.