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Poor Sleep Is Associated With Impaired Cognitive Function in Older Women: The Study of Osteoporotic Fractures

¹ San Francisco Coordinating Center and California Pacific Medical Center Research Institute.
² Departments of Psychiatry, Neurology, and Epidemiology, University of California, San Francisco and the San Francisco VA Medical Center.
³ Department of Psychiatry, University of California, San Diego and Veterans Affairs San Diego Healthcare System.
⁴ Department of Epidemiology, University of Pittsburgh, Pennsylvania.
⁵ Kaiser Permanente Center for Health Research, Northwest/Hawaii, Portland, Oregon.
⁶ Geriatric Research Education and Clinical Center and Center for Chronic Disease Outcomes Research, VA Medical Center, Minneapolis, Minnesota.
⁷ School of Medicine, University of Minnesota, Minneapolis.

Address correspondence to Terri Blackwell, MA, Senior Statistician, SF Coordinating Center, 185 Berry Street, Lobby 4, Suite 5700, San Francisco, CA 94107. E-mail: tblackwell{at}sfcc-cpmc.net

Background. The association between objectively measured sleep and cognition among community-dwelling elderly persons remains understudied. This observational, cross-sectional analysis examined this association.

Methods. Results are from 2932 women (mean age 83.5 years) in the Study of Osteoporotic Fractures between 2002 and 2004. Cognitive function was measured by Mini-Mental State Examination (MMSE) and Trail Making B Test (Trails B). Cognitive impairment was defined as MMSE < 26 or Trails B > 278 seconds. Sleep parameters measured objectively using actigraphy included total sleep time, sleep efficiency, sleep latency, wake after sleep onset (WASO), and total nap time.

Results. There were 305 women (10.6%) with MMSE < 26 and 257 women (9.3%) with Trails B > 278 seconds. Compared with women with sleep efficiency 70%, those with <70% had a higher risk of cognitive impairment (MMSE < 26 multivariate odds ratio [MOR] = 1.61; 95% confidence interval [CI], 1.20–2.16; Trails B > 278 MOR = 1.96; 95% CI, 1.43–2.67). Higher sleep latency was associated with higher risk of cognitive impairment (per half hour: MMSE < 26 MOR = 1.23; 95% CI, 1.13–1.33; Trails B > 278 MOR = 1.13; 95% CI, 1.04–1.24), as was higher WASO (per half hour: MMSE < 26 MOR = 1.15; 95% CI, 1.06–1.23; Trails B > 278 MOR = 1.24; 95% CI, 1.15–1.34). Women who napped 2 hours per day had a higher risk (MMSE < 26 MOR = 1.42; 95% CI, 1.05–1.93; Trails B > 278 MOR = 1.74; 95% CI, 1.26–2.40). There was no significant relationship for total sleep time.

Conclusion. Objectively measured disturbed sleep was consistently related to poorer cognition, whereas total sleep time was not. This finding may suggest that it is disturbance of sleep rather than quantity that affects cognition.