Poor sleep quality, not duration, linked to slower daily brain function in older adults

An analysis of the Einstein Aging Study data showed that older adults who experience longer nighttime wakefulness tend to have slower processing speed, worse working memory, and worse visual memory binding. On an individual level, participants’ processing speed was slower after nights with greater-than-usual nighttime awakenings. The research was published in Sleep Health: Journal of the National Sleep Foundation.

Sleep is essential for physical health, cognitive functioning, and emotional regulation. During sleep, the body repairs tissues, strengthens the immune system, and regulates hormones involved in appetite, stress, and growth. Adequate sleep supports memory consolidation and learning by helping the brain process and organize information. Poor or insufficient sleep is linked to increased risk of cardiovascular disease, obesity, diabetes, depression, and impaired immune function.

Sleep quality is determined by examining how well and how continuously a person sleeps. Key indicators of good sleep quality include short sleep onset latency (falling asleep easily), low wake after sleep onset (minimal time awake during the night), and high sleep efficiency (most time in bed spent asleep). Feeling rested and alert during the day is another important subjective indicator of good sleep. On the other hand, frequent awakenings, long periods of nighttime wakefulness, and excessive daytime sleepiness suggest fragmented or poor-quality sleep.

Study author Orfeu M. Buxton and his colleagues wanted to examine the short-term associations between sleep and daily cognitive performance in older individuals without dementia. They hypothesized that people experiencing longer nighttime wakefulness, later sleep midpoints, more napping, and shorter sleep durations would tend to have worse overall cognitive performance. On an individual level, the authors hypothesized that a person’s cognitive performance would be worse than average on the days following nights when their sleep was more fragmented (i.e., more nighttime awakenings).

The study authors analyzed data from the Einstein Aging Study. This study recruited participants from Bronx County, NY, who were community-residing, English-speaking, 70 years of age or older, free of dementia, and without significant hearing or vision loss or severe psychiatric symptoms that might interfere with cognitive testing. They also had no current alcohol or substance abuse issues or treatment for cancer within the last 12 months.

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This analysis used data from 261 participants. Their average age was 77.2 years, and 67% were women. Over 16 days, these individuals wore wrist actigraphs and completed cognitive assessments six times daily using smartphones provided by the study. An actigraph is a small wearable device, usually worn on the wrist, that measures movement over time to estimate sleep–wake patterns and overall rest–activity cycles.

The cognitive assessments consisted of four different tasks. They were designed to assess visuospatial working memory, processing speed, visual working memory (item-location binding), and visual working memory (intra-item feature binding). On average, the tasks took a total of 4–5 minutes to complete. Participants also completed a single night of home pulse oximetry (i.e., blood oxygen saturation and pulse rate measurements conducted during the night).

Results showed that participants who generally experienced longer nighttime wakefulness (wake after sleep onset) tended to have slower processing speed, worse working memory, and worse visual memory binding (a worse ability to integrate visual features into the memory of an object or scene). On an individual level, after nights with greater-than-usual nighttime wakefulness, participants tended to have below-average processing speed the next day.

Sleep duration, timing, and naps were not associated with performance on the cognitive tests.

“The results demonstrate short-term effects of sleep fragmentation (WASO) on processing speed the next day in dementia-free older adults. Better understanding short-term effects might identify individuals who may benefit from early interventions to prevent long-term cognitive decline,” the study authors concluded.

The study contributes to the scientific understanding of the consequences poor sleep quality has on cognitive performance. However, the participants in this study were all older adults. Results in other age groups might differ.

The paper, “Within- and between-person associations of sleep characteristics with daily cognitive performance in a community-based sample of older adults,” was authored by Orfeu M. Buxton, Qi Gao, Jonathan G. Hakun, Linying Ji, Alyssa A. Gamaldo, Suzanne M. Bertisch, Martin J. Sliwinski, Cuiling Wang, and Carol A. Derby.