Sleep Characteristics and Cognition in the Elderly

Effects of poor sleep on cognitive function are well known; most people have experienced them firsthand. In older adults, sleep dysfunction has been linked to cognitive impairment. Haba-Rubio and colleagues took a closer look at this association and reported their findings in a recent Neurology article.¹ They revealed the association of intermittent hypoxia with cognitive impairment in elderly individuals with sleep disorders.

The HypnoLaus study, a large, population-based, observational study, compared sleep characteristics of individuals older than 65 years of age with and without cognitive impairment. Of 580 study participants, 291 had cognitive impairment (50.2%). Significantly more participants with cognitive impairment were at risk of sleep apnea, as measured by the Berlin questionnaire (34.0% vs 25.1%, P=0.019). Subjective sleep characteristics other than the risk of sleep apnea did not differ significantly between the groups.

The objective sleep characteristics were evaluated using polysomnography, the gold standard of sleep evaluation. Compared to participants without cognitive impairment, participants with cognitive impairment: 1) spent more time in light sleep and less time in deep and rapid-eye movement (REM) sleep, 2) had lower sleep efficiency with higher intrasleep wake, 3) had more severe sleep-disordered breathing with a higher apnea/hypopnea index (18.0/hour vs 12.9/hour, P<0.001), and 4) had lower oxygen desaturation indices. Apnea/hypopnea index as well as oxygen desaturation indices, which serve as measures of hypoxia, were significantly associated with cognitive impairment.

Both characteristics of sleep-disordered breathing – sleep fragmentation and hypoxia – could be detrimental to cognitive function. Previous studies have linked sleep-disordered breathing to cognitive impairment; however, only measures of hypoxia were consistently associated with cognitive impairment across studies. In addition to implicating hypoxia in cognitive impairment, the present study identifies intermittent rather than continuous hypoxia as a contributing factor.

While population-based design, large sample size, and the use of polysomnography to objectively assess sleep are among the strengths of the study, cross-sectional design and low proportion of participants who underwent both cognitive testing and polysomnographic sleep evaluation (37.4%) limit the ability to elucidate the entire relationship between sleep parameters and cognitive impairment in individuals older than 65 years of age. 

“[Our] findings have major clinical implications given that sleep-disordered breathing is a common and treatable condition,” said the authors. “Indeed, studies suggest that sleep-disordered breathing treatment may partially restore cognitive impairment and slow cognitive deterioration.”

In the accompanying editorial, Auerback and Yaffe recognize the importance of this work as well as its limitations in the context of finding ways to prevent cognitive decline in the elderly.² They note that although evidence supporting aggressive treatment of sleep-disordered breathing is currently lacking, opportunities to improve the quality of life of these patients may still exist, and an evaluation of this population for both sleep-disordered breathing and cognitive decline may be appropriate.

References:

1. Haba-Rubio J, et al. Sleep characteristics and cognitive impairment in the general population: the HypnoLaus study. Neurology. 2017;88:463-469. 

2. Auerbach S, Yaffe K. The link between sleep-disordered breathing and cognition in the elderly: new opportunities? Neurology. 2017;88(5):424-425.