Cytokines and sleep: Effects on daytime sleepiness

Introduction: Sleep disturbances have been associated with chronic inflammation. This study examined the relationship between saliva cytokine concentrations and sleep and daytime sleepiness. Materials and methods: Healthy young Dutch students were recruited. After a normal night of sleep (without previous day alcohol consumption) previous night sleep quality was assessed using the Groningen Sleep Quality Scale. Daytime sleepiness was assessed with the Karolinska Sleepiness Scale (KSS), and single item ratings (0, absent, to 10, extreme) of sleepiness and being tired. In addition, the Fatigue-Inertia subscale of the Dutch version of the Profile of Mood States (POMS) scale was completed. Saliva was collected to determine cytokine concentrations of GM-CSF, IFN-γ, TNF-α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8 and IL-10. Sleepiness related outcomes were associated with cytokine levels using nonparametric Spearman correlations. Results: N=36 healthy subjects (38.9% men) with a mean (SD) age of 21.1 (1.8) years old participated in the study. Total sleep time correlated significantly with salivary TNF-α, IL-4, IL-5, IL-6, and IL-10 concentrations. No significant correlations were found with previous night's sleep quality. POMS-SF Fatigue-Inertia scores correlated significantly with IFN-γ and IL-2 concentrations, and KSS sleepiness scores correlated significantly with IFN-γ, IL-2, and TNF-α concentrations. The single item sleepiness and being tired score correlated significantly with IFN-γ and IL-2 concentrations. Conclusion: A significant positive correlation was found between salivary pro-inflammatory cytokine concentrations and daytime sleepiness. Total sleep time correlated significantly with daytime concentrations of both pro- and anti-inflammatory cytokines.