Associations of Sleep Characteristics With Cognitive Function and Decline Among Older Adults

V. Eloesa McSorley; Yu Sun Bin; Diane S. Lauderdale

Disclosures

Am J Epidemiol. 2019;188(6):1066-1075. 

In This Article

Abstract and Introduction

Abstract

Sleep laboratory studies find that restricted sleep duration leads to worse short-term cognition, especially memory. Observational studies find associations between self-reported sleep duration or quality and cognitive function. However self-reported sleep characteristics might not be highly accurate, and misreporting could relate to cognition. In the Sleep Study of the National Social Life, Health, and Aging Project (NSHAP), a nationally representative cohort of older US adults (2010–2015), we examined whether self-reported and actigraph-measured sleep are associated with cross-sectional cognitive function and 5-year cognitive decline. Cognition was measured with the survey adaptation of the multidimensional Montreal Cognitive Assessment (MoCA-SA). At baseline (n = 759), average MoCA-SA score was 14.1 (standard deviation, 3.6) points of a possible 20. In cross-sectional models, actigraphic sleep-disruption measures (wake after sleep onset, fragmentation, percentage sleep, and wake bouts) were associated with worse cognition. Sleep disruption measures were standardized, and estimates of association were similar (range, −0.37 to −0.59 MoCA-SA point per standard deviation of disruption). Actigraphic sleep-disruption measures were also associated with odds of 5-year cognitive decline (4 or more points), with wake after sleep onset having the strongest association (odds ratio = 1.43, 95% confidence interval: 1.04, 1.98). Longitudinal associations were generally stronger for men than for women. Self-reported sleep showed little association with cognitive function.

Introduction

Observational and experimental studies have found associations between sleep and cognitive function. The strongest and most consistent findings have been in experimental studies demonstrating a clear relationship between restricted sleep in a laboratory setting and next-day short-term performance in memory-related tasks.[1–5] Laboratory-based studies have also demonstrated relationships between sleep deprivation and other cognitive domains, including language, visuospatial ability, and decision-making, although findings for these have been less consistent (Alhola and Polo-Kantola,[6] review).

Sleep manipulated in laboratory environments differs by design from home sleep patterns, and there might be systematic differences between laboratory study volunteers—who are generally healthy and young—and paid adults in the community. Observational studies also demonstrate relationships between self-reported sleep characteristics among community-dwelling individuals and cognitive function.[7–10] However, survey responses on sleep duration have low to moderate correlation with sleep characteristics objectively estimated by either polysomnography or wrist actigraphy.[11–13] Reporting sleep duration could be cognitively challenging, because accurate answers require determining usual bedtime and waking time, which can have daily variation, and performing mental arithmetic, often around midnight. Additionally, inaccurate reporting has been linked to health determinants, including socioeconomic indicators, raising the possibility that associations between self-reported sleep and health outcomes could be biased.[12]

To address limitations of self-reported sleep characteristics, a few cohorts have added objective measures. For research about cognitive function, older adults are the population of greatest interest because they have the highest risk of cognitive decline and report worse sleep.[14] Two cohorts objectively measuring sleep have found associations between actigraphic indicators of poor sleep and cognitive impairment: the women-only Study of Osteoporotic Fractures (SOF) study and the men-only Osteoporotic Fractures in Men (MrOS) study.[15–18] Findings differed somewhat between the studies, suggestive of possible sex differences in the sleep-cognition relationship. Both cohorts used the Mini-Mental State Examination (MMSE) and the Trail Making Test Part B as measures of cognitive function. The Trail Making Test Part B is a test of executive function, and the MMSE is a widely used screening test for severe cognitive impairment and dementia, but has it has low sensitivity for mild cognitive impairment (MCI) or tracking moderate changes.[19–21]

In this study, we used data from a nationally representative cohort study of older adults that included a multidomain cognitive assessment sensitive to MCI to assess: 1) cross-sectional associations of actigraph-measured and self-reported sleep characteristics with cognitive function; and 2) longitudinal associations between sleep and 5-year decline in cognitive function. We examined whether associations differed for actigraphy and survey measures and investigated interactions by sex.

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