Sleep duration implicated in cognition
Both short and long sleep duration are associated with poorer cognitive outcomes, exerting a small negative effect on reaction time and visual memory, as reported in a recent study.
Researchers conducted a Mendelian randomization (MR) study with 77 single-nucleotide polymorphisms (SNPs) for sleep duration. They collected individual-participant data from the UK Biobank cohort (n=395,803; mean age, 56.9 years; 54 percent female) and summary statistics from the International Genomics of Alzheimer’s Project (cases: n=17,008; controls: n=37,154) to examine the potential impact of sleep duration on cognitive outcomes.
The average sleep duration in the cohort was 7.17 hours/day. There were U-shaped/inverted U-shaped patterns across sleep duration categories for most variables. Compared with those who reported sleeping for 7 hours/day, participants in both <7 and >7 hours/day sleep categories had lower scores in the baseline visual-memory and reaction-time tests.
The worst scores were observed among participants sleeping 10–12 hours/day (average number of incorrect matches in visual-memory test, 4.6; average reaction time, 591 milliseconds). Linear MR indicated that each additional hour/day of sleep slowed reaction time by 1 percent (p=0.008) and increased errors in visual-memory test by 3 percent (p=0.05).
There was, however, little evidence to support associations between increased sleep duration and visual memory decline (odds ratio [OR] per additional hour/day of sleep, 1.10, 95 percent CI, 0.76–1.57; p=0.62), reaction time decline (OR, 1.28, 0.49–3.35; p=0.61), all-cause dementia (OR, 1.19, 0.65–2.19; p=0.57) or Alzheimer’s disease risk (OR, 0.89, 0.67–1.18; p=0.41).
Meanwhile, nonlinear MR showed both short and long sleep duration to be associated with poorer visual memory (p-nonlinearity=3.44–9) and reaction time (p-nonlinearity=6.66–16).
The findings suggest that increased sleep duration may be causally related to poorer reaction time and visual memory, despite relatively small linear-effect sizes, the researchers said.
Therefore, improved sleep habits could represent a potential therapeutic target for cognition, which is important as there is currently no single-measure treatment that can decelerate cognitive decline or the risk of dementia, they added.