Background: Poor sleep quality is prevalent in older people and impairs their quality of life. Various studies show an association between sleep disorders and altered levels of inflammatory cytokines. The cytokine IL-1β has been shown to display both somnogenic and insomnia-promoting effects in experimental animals. Objectives: to evaluate the relationship between insomnia and salivary IL-1β concentration and the role of associated factors such as the symptoms of depression, use of hypnotics, intake of caffeinated beverages, smoking, and alcohol use in older individuals. An analytical, cross-sectional, observational research was carried out with a population of community-dwelling individuals over 60 years of age in Valencia (Spain). Sleep quality was measured with the Athens insomnia scale (AIS) and depressive symptoms with Geriatric Depression Scale (GDS). Results: 287 individuals participated in the study (mean age 74.08 years (76.7% women). 41.5% of the participants had insomnia, 36.9% took drugs for sleep problems, and 32.4% had relevant depressive symptoms. There was a significant inverse correlation between the IL-1β and total AIS score (rho = -0.302, p < 0.001), the sleep difficulty subdomain (rho = -0.259, p < 0.001), and the daytime sleepiness subdomain (rho = -0.322, p < 0.001). No significant correlation was observed between GDS and salivary IL-1β concentration. The IL-1β concentration was significantly lower in individuals taking drugs for sleeping compared with those not taking those drugs (1.11 ± 0.09 and 1.48 ± 0.08, respectively; p = 0.001). Regarding the AIS score, there was no significant difference in marital status, smoking, or the number of cups of tea or cola drinks, but there was a significant association with alcohol intake (p = 0.019) and in the number of daily intakes of coffee (p = 0.030). The receiver operating characteristic (ROC) curve analysis of IL-1β for diagnosis of moderate-severe insomnia showed an area under the curve (AUC) value of 0.78 (95% confidence interval 0.71-0.85). At the cut-off of 0.83 pg/µL of Il-1β, it had a sensitivity of 70.3% and a specificity of 69.8%.
Keywords: ageing; alcohol; cytokines; depressive symptoms; hypnotics; insomnia; sleep.