Association between sleep quantity and quality in early adulthood with cognitive function in midlife. Summary Background and objectives There is increasing evidence supporting an association between sleep quality and dementia risk. However, little is known about whether objectively measured sleep duration and quality influence cognition in midlife, a period of importance for understanding the direction of the association between sleep and dementia. We examined the association between sleep duration and quality , measured when participants were in their 30s and 40s, and midlife cognition assessed 11 years later among black and white adults. Methods As part of the Coronary Artery Risk Development in Young Adults Cohort Study, sleep duration and quality were assessed objectively using wrist actigraphy and subjectively using the Pittsburgh Sleep Quality Index (PSQI) between 2003 and 2005. During 2015-2016, we assessed midlife cognition using the Digit Symbol Substitution Test (DSST), the Stroop Test, the Rey Auditory Verbal Learning Test, the Montreal Cognitive Assessment (MoCA), and the letter fluency and category fluency. We used multivariable logistic regression to examine the association between sleep parameters and poor cognitive performance, which was defined as a score >1 SD below the mean score. Results The 526 participants (58% women and 44% black) had a mean age of 40.1 ± 3.6 years at baseline, a mean sleep duration of 6.1 ± 1.1 hours, and a mean fragmentation index. sleep (calculated as the sum of the percentage of time spent moving and the percentage of immobile periods ≤1 minute) of 19.2 ± 8.1%, and 239 (45.6%) participants reported having sleep problems as assessed defined by a global PSQI score of >5. After adjustment for demographics, education, smoking, body mass index, depression, physical activity, hypertension, and diabetes, those in the highest versus lowest tertile of the sleep fragmentation index were more than twice as likely to have a poor cognitive performance (>1 SD below the mean) on the DSST (odds ratio [OR] = 2.97; 95% CI 1.34–6.56), fluency (OR = 2.42; 95% CI 1 .17–5.02) and MoCA test (OR = 2.29; 95% CI 1.06–4.94). The association between sleep fragmentation and cognitive performance did not differ by race or sex. Objective sleep duration or subjective sleep quality were not associated with cognition in midlife. Discussion High sleep fragmentation measured with actigraphy rather than sleep duration was associated with worse cognition among middle-aged black and white men and women. Sleep quality is important for cognitive health even in middle age. |
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American Academy of Neurology
People who have more sleep disorders in their 30s and 40s may be more likely to have memory and thinking problems a decade later, according to new research published in the issue in Neurology , the medical journal of the American Academy of Neurology. The study does not prove that sleep quality causes cognitive decline. It only shows an association.
"Since signs of Alzheimer’s disease begin to accumulate in the brain several decades before symptoms begin, understanding the connection between sleep and cognition earlier in life is critical to understanding the role of sleep problems as a risk factor for the disease," said the author of the study. Yue Leng, PhD, of the University of California, San Francisco. "Our findings indicate that the quality, rather than the quantity, of sleep is most important for cognitive health in midlife."
526 people with an average age of 40 years participated in the study. They were followed for 11 years.
The researchers looked at the duration and quality of the participants’ sleep. Participants wore a wrist activity monitor for three consecutive days on two occasions about a year apart to calculate their averages. The participants slept an average of six hours.
Participants also reported bedtime and wake times in a sleep diary and completed a sleep quality survey with scores ranging from zero to 21, with higher scores indicating worse sleep quality. A total of 239 people, or 46%, reported poor sleep with a score above five.
Participants also completed a series of memory and thinking tests.
The researchers also looked at sleep fragmentation , which measures brief, repetitive interruptions to sleep. They looked at both the percentage of time they spent moving and the percentage of time they spent not moving for a minute or less during sleep. After adding these two percentages, the researchers found that participants had an average sleep fragmentation of 19%.
The researchers then divided the participants into three groups based on their sleep fragmentation score.
Of the 175 people with the most interrupted sleep, 44 had poor cognitive performance 10 years later, compared to 10 of the 176 people with the least interrupted sleep.
After adjusting for age, gender, race, and education, people with the most interrupted sleep were more than twice as likely to have poor cognitive performance compared to those with the least interrupted sleep. There were no differences in cognitive performance in midlife between those in the middle group compared to the group with the least interrupted sleep.
"More research is needed to evaluate the link between sleep disorders and cognition at different stages of life and to identify whether there are critical periods of life when sleep is most strongly associated with cognition," Leng said. "Future studies could open up new opportunities for preventing Alzheimer’s disease in the future."
The amount of time people slept and their self-reports of their sleep quality were not associated with cognition in midlife.
One limitation of the study was that, due to the small sample size, the researchers were not able to fully investigate potential racial or gender differences.
The study was funded by the National Institute on Aging and the National Heart, Lung, and Blood Institute.
