Sleep quality at age 40 linked to cognitive function a decade later
US researchers found that objectively recorded interrupted sleep at around age 40 was associated with an increased likelihood of poor cognitive performance 11 years later. Sleep duration and subjective assessment of sleep quality did not demonstrate an association with cognitive function. A report of the work is published in the journal Neurology.
The association of sleep disorders with the presence of dementia is well known. In this case, pathological changes in the brain begin to occur much earlier (sometimes for decades) than the first manifestations of the disease appear. In this regard, the relationship between the quantity and quality of sleep and cognitive functions in middle age and their possible consideration as a risk factor for the development of dementia in the future is of interest. However, there is very little objective data on this issue.
To obtain them, Yue Leng (Yue Leng) with colleagues at the University of California at San Francisco conducted additional work with 526 participants (58 percent - women; 44 percent - black) population cohort study CARDIA. From 2003-2005, when the mean age was 40.1 ± 3.6 years, the quantity and quality of their sleep was measured objectively using wrist actigraphy and subjectively using the Pittsburgh Sleep Quality Scale (PSQI). In 2015-2016, participants' cognitive function was assessed using the Digit Symbol Substitution Test (DSST), Stroop's word-numeric, Ray's Auditory Verbal Learning Test (RAVLT), letter and item category fluency, and the Montreal scale (MoCA).
At baseline, the mean sleep duration was 6.1 ± 1.1 hours and the mean sleep fragmentation index (calculated as the sum of the proportions of moving time and nonmoving periods lasting no more than a minute of total sleep duration) was 19.2 ± 8.1 percent. 239 (45.6 percent) participants rated their sleep as poor (total PSQI score less than five). Values that were below the mean by more than one standard deviation were taken as poor cognitive performance. Its relationship with sleep parameters was assessed by multivariate logistic regression with adjustments for demographics, education level, smoking, body mass index, physical activity, depression, arterial hypertension and diabetes mellitus.
It was found that those in the upper tercile on the sleep fragmentation index were more than twice as likely to have low cognitive performance on the DSST (odds ratio 2.97; 95 percent confidence interval 1.34-6.56); letter and item category freedom (odds ratio 2.42; 95 percent confidence interval 1.17-5.02) and MoCA (odds ratio 2.29; 95 percent confidence interval 1.06-4.94) compared with those in the lower tercile. This correlation was independent of gender and ethnicity. No such relationship was found for the objective measure of sleep duration and subjective assessment of sleep quality.
The results suggest that objective assessment of sleep quality in middle age by its fragmentation, but not other parameters, is associated with reduced cognitive functions in later life. It deserves further study as a potential risk factor for dementia, which may help in developing strategies to prevent the disease, the authors of the paper conclude.
In 2023, Swedish and Australian researchers reported that they failed to detect an effect of delaying the alarm clock on cognitive function, mood and feeling sleepy after waking up.