Future directions for sleep and cognition research in at-risk older adults

Abstract

Siddarth et al. (2020)’s paper added new findings to the evidence on relationship between sleep and cognitive function. In their paper, poor sustained attention was strongly associated with self-reported sleep quality measured with the Pittsburgh Sleep Quality Index (PSQI; Buysse et al., 1989) among middle-aged and older adults with mild subjective memory complaints. Their work enhances our understanding of subjective cognitive function across multiple cognition domains among adults with existing memory complaints, diagnosed using transitional staging models from normal cognition to Alzheimer’s disease or other types of dementia. Although Siddarth and colleagues did not focus on examining the mechanisms linking sleep and cognitive aging (which are still poorly understood), their findings suggest the importance of subjective sleep quality in relation to subjective and objective cognition. Prior studies have shown strong associations between subjective and/or objective sleep and cognitive function among healthy adults both in crosssectional and longitudinal study designs. Both objectively measured poor sleep (e.g. low sleep efficiency, increased sleep latency, wake after sleep onset, fragmentation; Campbell et al., 2020; Yaffe et al., 2014) and self-reported sleep complaints (Campbell et al., 2020; Tardy et al., 2015; Yaffe et al., 2014) are significantly associated with worse cognitive function in older adults; however, subjective sleep quality as measured by the PSQI and objective sleep are not consistently correlated with each other in middle-aged and older adults (Landry et al., 2015). Some sleep indices (e.g. snoring, nightmares) are difficult for people to self-assess and report; thus, objectivelymeasured sleep parameters (e.g. sleep stages, electroencephalogram power values, sleep fragmentation) using polysomnography or actigraphy may help to further elucidate underlying mechanism of sleep and cognitive function, particularly among those who are already experiencing subjective and/or objective memory decline. Siddarth and colleagues focused on subjective sleep quality and did not measure objective parameters of sleep. Nevertheless, we agree with their argument addressing that subjective sleep complaints could predict future cognitive impairment and dementia even in the absence of objective cognitive impairment. In other words, perceived poor sleep may play a role as an early symptomatic marker in the spectrum of developing Alzheimer’s disease or other types of neurodegeneration. Pending further evidence of contribution of subjective sleep on cognitive decline, monitoring self-reported symptoms of poor sleep may be served as a more cost-effective and easier method to identify at-risk group in combination with biomarkers, neuroimaging, and other clinical features. Additionally, patients’ own assessment of their sleep is important as their own view of sleep may motivate them to engage in cognitive behavioral therapies (e.g. Cognitive Behavioral Therapy for Insomnia [CBT-I]) that have been shown to improve sleep quality (Qaseem et al., 2016). Siddarth et al. (2020)’s paper extended the evidence on the importance of role of sleep on cognition to more broad groups of older adults from those who already had clinically significant cognitive impairments. The special issue (Volume 32, Issue 7) published in July 2020 in the International Psychogeriatrics discussed sleep and sleep disorders among different groups of older adults. Papers in the issue confirm significant relationship between sleep and cognitive function or other health outcomes such as depression among older adults with neurodegenerative disorders associated with cognitive impairment (e.g. Parkinson’s disease, nursing home residents with dementia). Overall, the clinical message from these findings was sleep as a potential target to prevent further cognitive deterioration and/or psychological well-being. On the other hand, Siddarth et al. (2020)’s paper examined older adults who may be at-risk for cognitive decline and reported subjective memory complaints without major cognitive impairment (i.e. dementia). Taken together, monitoring sleep patterns and screening chronic sleep problems such as insomnia may be one way to prevent or delay worsening cognitive impairments and related health issues among older adults with all stages of cognitive function. Indeed, Siddarth et al. proposed a future sleep intervention study to test whether improved sleep could improve memory consolidation. A few intervention studies have found that improving sleep with CBT-I is associated with improved objective International Psychogeriatrics (2021), 33:7, 655–658 © International Psychogeriatric Association 2021