Trouble Falling Asleep Predicts Later Cognitive Impairment

Trouble falling asleep predicted cognitive impairment 14 years later, a longitudinal analysis showed.

Of all insomnia symptoms, only trouble falling asleep was linked to later cognition, reported Afsara Zaheed, MS, a PhD candidate at the University of Michigan in Ann Arbor, at SLEEP 2021, a joint meeting of the American Academy of Sleep Medicine and the Sleep Research Society.

More frequent trouble falling asleep predicted poorer episodic memory, executive function, language, and processing speed performance, Zaheed said.

Links between sleep initiation and cognition later in life were explained partly by both depressive symptoms and vascular disease in 2014 for all domains except episodic memory, which was partly explained only by depressive symptoms.

“While there is growing evidence for a link between insomnia and cognitive impairment in older adults, it has been difficult to interpret the nature of these associations given how differently both insomnia and cognitive impairment can present across individuals,” Zaheed said in a statement.

“By investigating associations between specific insomnia complaints and cognition over time using strong measures of cognitive ability, we hoped to gain additional clarity on whether and how these different sleep problems may lead to poor cognitive outcomes,” she added.

The study used Health and Retirement Study data of 2,496 adults at least 51 years old. Participants reported baseline insomnia symptoms in 2002, including frequency of trouble falling asleep, nighttime awakenings, early awakenings, and feeling rested upon awakening. Cognition was assessed in 2016 as part of the Harmonized Cognitive Assessment Protocol, which looked at five cognitive domains: episodic memory, executive function, language, visuoconstruction, and processing speed.

Analyses controlled for demographics and baseline global cognitive performance. Mediation models tested whether associations were explained by self-reported depressive symptoms or vascular disease in 2014, controlling for baseline values.

Depressive symptoms were assessed with the eight-item Center for Epidemiologic Studies Depression Scale (CES-D). Vascular disease burden was the sum of the presence of hypertension, heart disease, diabetes, and stroke.

Women reported more frequent insomnia symptoms, more depressive symptoms, and less vascular disease than men. They also demonstrated better episodic memory, worse executive function, and worse visuoconstruction performance. Despite this, associations among insomnia symptoms, mental and physical health mediators, and cognition did not differ by sex.

“Although additional research is necessary to confirm these findings and prove causality, this study provides further evidence of the importance of sleep to brain health,” observed Nathaniel Watson, MD, MSc, of UW Medicine in Seattle, who wasn’t involved with the study.

“Sleep health and sleep behaviors are often modifiable,” Zaheed noted. “These results suggest that regular screening for insomnia symptoms may help with tracking and identifying people with trouble falling asleep in mid-to-late life who might be at risk for developing cognitive impairments later in life.”

“Additional intervention research is needed to determine whether intervening on insomnia symptoms can help prevent or slow the progression of cognitive impairments in later life,” she added. Future research also may uncover mechanisms like amyloid aggregation, circadian disruption, or inflammation.

The study had several limitations: the comprehensive cognitive assessment was administered only once, and insomnia and mediators were assessed with brief self-reported measures.