Long night’s sleep staves off daytime sleepiness
medwireNews: Sleepiness in the day appears to be primarily associated with the amount of sleep an individual gets the night before, suggests a prospective study across 42 days of normal living.
Other contributing factors include poor sleep quality, early rising, and poor health, say the study researchers.
"Assuming that sleepiness is non-conducive to efficient functioning, the results suggest that at least some of the variations between 'good' and 'bad' days may be due to variations in sleep duration and sleep quality," they comment.
The team, led by Torbjörn Åkerstedt (Stockholm University, Sweden), note that their study shows the factors contributing to daytime sleepiness during "average, non-pathological and non-extreme sleep patterns." The associations were therefore modest, but are likely to be stronger with more variable sleep patterns.
Fifty healthy volunteers, aged 18 to 61 years, participated in the study and kept daily diaries detailing sleep quality, while daytime sleepiness was rated every second hour of being awake.
The participants' average total sleep time was 7.4 hours, with the average shortest sleep time of all participants 4.5 hours and the longest 10.2 hours. The average Karolinska Sleepiness Scale (KSS) score was 4.1 and the average sleep quality index rating was 4.1 out of a possible 5.0.
In multivariate analysis, sleepiness increased with shorter preceding sleep duration. For each hour of reduced sleep, the KSS score fell by 0.16 points.
"The tight day-to-day coupling observed over time adds credibility to the notion that sleep duration is coupled directly with the daytime level of sleepiness in a dose-response relationship," the researchers comment in the Journal of Sleep Research.
The other major predictor of daytime sleepiness was poor subjective health. Although unable to determine the direction of causation, the researchers refer to extensive research showing a link between sleep-inducing inflammatory cytokines, such as interleukin-6, and poor health, suggesting poor health as a cause of increased sleepiness.
Sleep quality, time of awakening, and napping were also associated with daytime sleepiness but to a lesser extent. The researchers point out that, "while napping may be seen as an effective countermeasure to sleepiness, in this study it seemed, rather, to appear as a response to sleepiness."
medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013
By Lucy Piper, Senior medwireNews Reporter