Summary: Sleep duration can have a negative impact on memory skills and reaction time. While the effects of sleep deprivation are well documented, researchers report sleeping for longer than the recommended 7 to 8 hours per night is associated with more errors in memory recall and slower reaction times, with each additional hour of sleep impacting performance more.
Sleeping for less than seven hours or more than nine hours could adversely affect cognitive performance such as visual memory and reaction time, according to a new UCL study.
The study, published in the International Journal of Epidemiology, is the first to examine whether there is a potential causal link between sleep and cognitive function and dementia by analysing genes associated with sleep duration using the Mendelian randomization method.
Researchers found that people who slept for less than seven hours a day made 5% more errors per each hour less of sleep in a visual memory test, whilst those who slept for more than nine hours made even more errors (9% per each additional hour of sleep) in this test. On average, the study participants made 3% more errors in the visual memory test and had around a 1% slower reaction time for each additional hour of sleep a day.
Lead author, PhD candidate, Albert Henry (UCL Institute of Cardiovascular Science) said: “Our study provides new evidence that both short and long sleep may have a negative impact on certain cognitive domains, such as visual memory and reaction time.”
The researchers analysed data from nearly 400,000 participants from UK Biobank as well as data from the International Genomics of Alzheimer’s Project. By analysing genetic data the researchers were able to minimise reverse causation and confounding, both of which have been important limitations of previous studies.
Dr Victoria Garfield (UCL Institute of Cardiovascular Science), the senior author explained: “We conducted a large Mendelian randomization (MR) study to identify the potential causal role of sleep duration on multiple cognitive outcomes.”
“This is the first time that we were able to assess a person’s lifelong sleep duration in relation to cognitive function, as opposed to only looking at how sleep is linked to these outcomes at only one point in time.”
“We would recommend that most healthy adults follow the recommendation of seven to nine hours of sleep.”
Henry added, “Previous studies have also linked sleep problems with an increased risk of dementia. We found little evidence that sleep duration is associated with the risk of dementia in the present study, but more research is needed to explore this relationship.”
“Overall, our study highlights the importance of sleep duration in relation to cognitive function. This suggests that improving sleep habits may be beneficial for cognitive health.”
Rowan Walker – UCL
The image is credited to UCL.
Original Research: Open access
“The relationship between sleep duration, cognition and dementia: a Mendelian randomization study “. Albert Henry, Michail Katsoulis, Stefano Masi, Ghazaleh Fatemifar, Spiros Denaxas, Dionisio Acosta, Victoria Garfield, Caroline E Dale.
International Journal of Epidemiology. doi:10.1093/ije/dyz071
The relationship between sleep duration, cognition and dementia: a Mendelian randomization study
Short and long sleep duration have been linked with poorer cognitive outcomes, but it remains unclear whether these associations are causal.
We conducted the first Mendelian randomization (MR) study with 77 single-nucleotide polymorphisms (SNPs) for sleep duration using individual-participant data from the UK Biobank cohort (N = 395 803) and summary statistics from the International Genomics of Alzheimer’s Project (N cases/controls = 17 008/37 154) to investigate the potential impact of sleep duration on cognitive outcomes.
Linear MR suggested that each additional hour/day of sleep was associated with 1% [95% confidence interval (CI) = 0–2%; P = 0.008] slower reaction time and 3% more errors in visual-memory test (95% CI = 0–6%; P = 0.05). There was little evidence to support associations of increased sleep duration with decline in visual memory [odds ratio (OR) per additional hour/day of sleep = 1.10 (95% CI = 0.76–1.57); P = 0.62], decline in reaction time [OR = 1.28 (95% CI = 0.49–3.35); P = 0.61], all-cause dementia [OR = 1.19 (95% CI = 0.65–2.19); P = 0.57] or Alzheimer’s disease risk [OR = 0.89 (95% CI = 0.67–1.18); P = 0.41]. Non-linear MR suggested that both short and long sleep duration were associated with poorer visual memory (P for non-linearity = 3.44e–9) and reaction time (P for non-linearity = 6.66e–16).
Linear increase in sleep duration has a small negative effect on reaction time and visual memory, but the true association might be non-linear, with evidence of associations for both short and long sleep duration. These findings suggest that sleep duration may represent a potential causal pathway for cognition.