Trouble Falling Asleep a Modifiable Risk Factor for Dementia?

Megan Brooks

June 15, 2021

Difficulty falling asleep may be predictive of future cognitive impairment in older adults ― and depressive symptoms and vascular disease may partially drive this association, new research suggests.

Trouble falling asleep "may be a modifiable risk factor for later-life cognitive impairment and dementia," said lead author Afsara Zaheed, PhD candidate in clinical science, Department of Psychology, University of Michigan, Ann Arbor, Michigan.

"Patients should also be aware of the importance of insomnia on cognitive functioning so that they can bring up these concerns with their providers early," she told Medscape Medical News.

The findings were presented at SLEEP 2021: 35th Annual Meeting of the Associated Professional Sleep Societies.

Poor Sleep Common With Age

As many as one half of older adults report having poor sleep quality and insomnia, and growing evidence suggests that insomnia may be a unique risk factor for cognitive decline in later life, Zaheed explained.

To investigate further, the researchers analyzed data on 2496 adults aged 51 years and older who were participants in the Health and Retirement Study, a longitudinal study of aging in a nationally representative population of older adults.

In 2002, participants were asked how often they had trouble falling asleep, woke up during night, woke up too early, and were not able to fall asleep again and how often they felt really rested when they woke up in the morning.

In 2016, participants' cognition was assessed using a battery of neuropsychological tests that gauged episodic memory, executive function, language, visuospatial/construction, and processing speed.

Analyses controlled for sociodemographics and baseline global cognitive performance and the influence of depressive symptoms and vascular disease.

Compared with other insomnia symptoms, having difficulty falling asleep in 2002 was the main insomnia symptom that was predictive of cognitive impairment 14 years later, in 2016.

More frequent trouble falling asleep was predictive of poorer episodic memory, executive function, language, processing speed, and visuospatial performance.

The associations between sleep initiation and later cognitive impairment were partially explained by depressive symptoms and vascular disease burden for all domains except episodic memory, which was only partially explained by depressive symptoms.

Unclear Mechanism

Zaheed said research is needed to uncover neurophysiologic mechanisms underlying the observed associations.

"It may be that chronic difficulty with falling asleep is associated with inflammatory or metabolic processes that negatively affect brain structure and function over time," she said.

"Insomnia has also been linked with higher accumulation of protein aggregates in the brain that disrupt cell communication and are characteristic of late-life disorders such as Alzheimer's disease," she added.

"While our project did not directly investigate these potential causal pathways between insomnia and cognition, our results suggest that investigating these potential mechanisms is an important area for future research," Zaheed said.

"While additional intervention research is needed to determine whether targeting insomnia in older patients can have lasting cognitive benefits, results from this study suggest that discussing insomnia symptoms at the primary care level may be beneficial for both doctors and patients," Zaheed added.

"By targeting insomnia ― for example, through an evidence-based cognitive-behavioral therapy approach ― individuals may improve various mental and physical health outcomes in addition to improving their sleep quality," Zaheed said.

Reached for comment, Shaheen E. Lakhan, MD, PhD, neurologist in Newton, Massachusetts, said, "There is a strong link between chronic sleep disturbances and cognitive impairment, including dementia.

"This study further supports this link and specifically calls out initiating sleep (as opposed to staying asleep) as the culprit. It also raises the hypothesis that the link is primarily mediated by depression and vascular disease; however, the verdict is still out," said Lakhan.

The study was funded by the National Institute on Aging. Zaheed and Lakhan have disclosed no relevant financial relationships.

SLEEP 2021: 35th Annual Meeting of the Associated Professional Sleep Societies: Abstract 537. Presented June 9, 2021.

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