Both fatigue and sleep quality were identified as potential risk factors linking sleep duration and self-rated health.
Data from a recent study suggest unhealthy sleep duration, defined as longer or shorter than 7 to 9 hours a night, as well as worse sleep quality, were associated with poorer self-rated health (SRH). Although those who slept for longer durations may experience better SRH in the event that they have good sleep quality, for those with shorter durations, SRH was independent of sleep quality. Investigators also observed current fatigue and sleep quality, which were identified as factors linking sleep duration and SRH.
The study included a total of 1304 individuals, with a median age of 28.8 years (range, 18-79). Women represented 57% of participants, and all completed surveys inquiring about general SRH, sleep duration and quality from the night before, as well as current impressions of fatigue. Data on fatigue was collected from 1149 (88.1%) participants.
Short sleepers (b = –0.51 [95% CI, –0.72 to –0.29]; P <.001) and long sleepers (b = –0.27 [95% CI, –0.50 to –0.03]; P = .029) reported significantly lower SRH when compared with “normal” sleepers (M = 7.91; standard error = 0.14). Participants with poor sleep quality had significantly lower SRH than those with intermediate sleep quality (b = –0.29 [95% CI, 0.56 to –0.03]; P = .032). Significantly higher SRH was reported by those with good sleep quality, when compared with those with intermediate sleep quality (b = 0.68 [95% CI, 0.48-0.89]; P <.001). Additionally, investigators found that the linear term of sleep quality moderated the quadratic relationship of SRH and sleep duration (b = 0.01 [95% CI, 0.00-0.01]; P = .001).
“A significant point to be taken from the current results is the importance of assessing both sleep duration and sleep quality when investigating sleep-health relationships. Last night's long sleep duration does not seem to be associated with poor subjective health unless it is coupled with poor sleep quality,” first author Anna Andreasson, PhD, MSc, BMed, external researcher, Stress Research Institute, and associate professor of psychology, Stockholm University, Sweden; associate professor of clinical epidemiology, Karolinska Instituet, Sweden; and honorary associate professor, Macquarie University, NSW, Australia, et al wrote. “Poor sleep quality, as well as poor SRH, are potentially factors that make an individual prioritize sleeping longer. The current results suggest that future studies on the potential health risks of long sleep will benefit from including measures of sleep quality.”
When addressing the role that fatigue plays in affecting sleep quality, a generalized structural equation model was used, which showed that SRH (b = 0.66 [95% CI, 0.33-0.98]; P <.001) was mediated by sleep quality (b = 0.30 [95% CI, 0.20-0.40]; P <.001). Sleep quality was found to partially mediate the quadratic relationship between sleep duration and SRH when using sleep quality as a mediating variable (b = 0.36 [95% CI, 0.04-0.68]; P = .029).
As second model found that fatigue (b = 0.27 [95% CI, 0.12-0.41]; P <0.001) also significantly mediated the quadratic relationship of sleep duration with SRH (b = 0.76 [95% CI, 0.36-1.17]; P <.001). Additionally, sleep duration remained significantly associated with SRH (b = 0.50 [95% CI, 0.11; 0.88]; P <.001), leading investigators to concluded that the quadratic relationship between SRH and sleep duration was partially mediated by fatigue.
The study was limited due to subjective and self-reported measurements, opening up further potential for undiagnosed sleep apnea or insomnia as well as bias. The study was also limited to data from the last night’s sleep, which may not account for chronic short or long sleep duration or varying sleep quality. Investigators also noted the observational nature of the study, the potential for an indirect relationship between sleep and SRH, and the sample’s majority of young and health individuals.