A new study provides more evidence that insomnia may contribute to cognitive decline in older adults and shows that difficulty falling asleep in midlife may be most indicative of future cognitive impairment.
Investigators found that having trouble falling asleep on most nights (vs rarely/never) was equivalent to the effect of 2 to 3 years of aging across cognitive domains 14 years later.
Interventions to reduce insomnia, with a focus on difficulty initiating sleep, may be a target to optimize cognitive aging, say the researchers, led by Afsara Zaheed, PhD candidate, Department of Psychology, University of Michigan, Ann Arbor.
Preliminary results from the study were presented during SLEEP 2021: 35th Annual Meeting of the Associated Professional Sleep Societies and were reported Medscape Medical News at the time. The full study results were published online October 30 in the journal Sleep.
Health and Retirement Study
The researchers analyzed data on 2595 adults (mean age, 64 years; 65% women) who were enrolled in the long-running Health and Retirement Study.
In 2002, participants were asked about the frequency of their having trouble falling asleep, waking during the night, waking too early, and feeling unrested in the morning. In 2014, depressive symptoms and vascular conditions were assessed.
In 2016, participants’ cognition was assessed using a battery of neuropsychological tests that gauge episodic memory, executive function, language, visuospatial/construction, and processing speed.
The researchers performed a series of analyses in which they controlled for sociodemographics and baseline global cognitive performance and the influence of depressive symptoms and vascular disease.
The results showed that frequent difficulty initiating sleep was associated with poorer episodic memory, executive function, language, visuoconstruction, and processing speed 14 years later ― equivalent to 2.2 to 3.4 years of aging.
No other insomnia symptoms were associated with cognitive decline. This supports prior research suggesting that cognitive impairment in older adults is more strongly associated with difficulty initiating sleep rather than difficulty maintaining sleep, the researchers note.
The association was not modified by gender. However, women were more likely than men to report frequent trouble falling asleep.
Blame It on Depression?
Consistent with prior research, frequent difficulty initiating sleep was associated with greater depressive symptoms and vascular disease burden.
Depressive symptoms accounted for 12% to 20% of variance in these associations, and vascular disease accounted for 6% to 15% of variance in nonmemory associations.
Ties between trouble falling sleep and later cognitive problems observed in the current study are in line with growing evidence of a relationship between circadian dysfunction and neurodegenerative diseases.
For example, delayed circadian rhythms, which can manifest as difficulty falling asleep or chronic sleep-onset insomnia, were prospectively associated with a nearly twofold greater risk of mild cognitive impairment or dementia over 5 years in a community-dwelling sample of older women.
“These findings have relevant implications for clinical practice, as sleep initiation difficulties may alert providers to patients at heightened risk for subsequent cognitive impairment,” the researchers note.
The investigators note that future intervention research is needed to better understand the mechanisms and modifiability of associations between difficulty initiating sleep and cognition later in life and which interventions reduce late-life cognitive impairment and gender disparities in cognitive aging.
Clearing the Cobwebs
Commenting on the findings for Medscape Medical News, Shaheen Lakhan, MD, a neurologist and researcher from Boston, Massachusetts, said this line of research is “incredibly important” in tackling age-related cognitive decline.
“Sleep has always been thought to be restorative, but only recently has modern day neuroscience shown that quality sleep actually clears the cobwebs that accumulates during wakefulness,” Lakhan said.
“Contrary to what many believe, the brain is quite active during sleep and actually resets itself, and similar to how your computer boots up, so does the brain with either clearing or caching memory files and activating different processes. The brain has a garbage disposal system that clears its waste largely in sleep that accumulated during wakefulness,” he added.
“It is important to separate two major sleep problems ― falling asleep and staying asleep ― and appears through this line of research that the former correlates the most with decline of brain health over the years.
“Similar to your computer when you try to shut down but there are files open or buggy apps that prevent it from happening, depression, anxiety, pain, and stress in general all impair falling asleep and are independently associated with worsening cognitive function, too.”
Lakhan added that greater emphasis should be placed on falling asleep to protect the brain from deterioration over decades.
Sleep. Published online October 30, 2022. Abstract