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A new sleep study, performed by researchers at the University of Chicago, measured sleep quality in older adults and found conflicting results. The researchers used two different ways of measuring sleep. One involved asking study members about their sleep and sleep problems. The other relied on a motion-detecting wrist actigraph. Self-reports from the participants and the more objective measures from the wrist sensor often led to differing assessments of their sleep.
The measures of sleep disruption captured by the actigraph were all associated with cognitive function. On average, more disrupted sleep was associated with worse cognitive function. The strongest sleep-related predictor of declining cognitive function was the average number of minutes a person was awake during the night — what researchers call “wake after sleep onset” or WASO.
Self-reported sleep problems were not associated with cognitive function measured at the time, or with cognitive decline over five years.
Cognitive function was measured using a version of the Montreal Cognitive Assessment (MOCA) that was adapted for such survey research studies. The MOCA is a standard tool used by clinicians to determine the presence of mild cognitive impairment. The test asks questions that probe attention, abstraction, orientation, executive function, memory and language.
The MOCA questions were asked at about same time as sleep was measured and then again five years later. The difference in the answers over the five years was used to determine which participants had declining cognitive function.
According to study author Diane Lauderdale, PhD, professor and chair of Public Health Science at the University of Chicago, actigraphs “provide valid estimates of sleep characteristics when compared with polysomnography— a laboratory test that measures sleep by attaching multiple sensors to the patient’s head, chest and limbs.”
Study subjects in this study wore an actigraph for several nights and were able to go about their usual routines. “It doesn’t change how well they sleep or when they sleep,” Lauderdale said, “so it provides a good estimate of how people normally sleep at home, which may vary from night to night.” The device is worn on the wrist not used for writing.
The study began in 2010-11. A team based at the University of Chicago recruited 759 people for the sleep study, part of the National Social Life, Health and Aging Project (NSHAP). All of the study participants were already participating in NSHAP, a nationally representative study population of older adults.
All were born between 1920 and 1947. The youngest volunteers were 62 years old at the beginning of the study. The oldest was 95 when it ended in 2015-16. The average age was 72.
Adults in this age group often report sleep problems. They may have trouble falling asleep, difficulty staying asleep, waking up earlier than expected, or not feeling rested in the mornings. These sleep problems define an insomnia diagnosis.
“We found that more disrupted sleep is, on average, related to worse cognitive function, but only when sleep was measured objectively using the actigraph,” Lauderdale said. “Reporting sleep difficulties isn’t a risk factor for cognitive decline. The problem seems to be an inability to sleep in a consolidated way, spending significant time awake during the night. People may not be aware of this, or they may report having difficulty staying asleep but have relatively good sleep when measured by the actigraph.”
“Curiously,” she added, “more disrupted sleep had a stronger effect on cognitive decline for men than women.”
The total amount of sleep for study participants was not related to cognitive function when measured by the actigraph or by asking people how long they usually sleep.
The National Social Life, Health and Aging Project (NSHAP) is a population-based study of health and social factors on a national scale, aiming to understand the well-being of older, community-dwelling Americans by examining the interactions among physical health, illness, medication use, cognitive function, emotional health, sensory function, health behaviors and social connectedness. It is designed to provide health providers, policy makers and individuals with useful information and insights into these factors, particularly their impact on social and intimate relationships.
The National Institute on Aging of the National Institutes of Health supported this research. The study, “Associations of Sleep Characteristics with Cognitive Function and Decline among Older Adults,” was published online in the American Journal of Epidemiology. Additional authors were Eloesa McSorley at the University of Chicago and Yu Sun Bin at the University of Sydney.