Longitudinal association between sleep disturbance and inflammation, and the role of positive affect.

Previous longitudinal evidence suggested that sleep disturbance (i.e., difficulties in sleep onset and sleep maintenance) may be longitudinally associated with systemic inflammation, which is involved in the pathophysiology of mental and somatic illness. The mechanisms underlying this association, however, remain largely unexplored. In the context of health psychology, a substantial body of literature showed that positive affect may have a favourable impact on immune and inflammatory response and buffer the proinflammatory effects of stress. Therefore, the aim of this study was to assess whether subjective sleep disturbance is longitudinally associated with serum high sensitivity C-reactive protein (hs-CRP), a marker of systemic inflammation, and whether this association is mediated by a decrease in positive affect. The data of 1894 participants aged 64.11 ± 8.02 years from the English Longitudinal Study of Ageing (ELSA) across three waves of data collection were analysed. Self-reported sleep disturbance was assessed in 2008-2009, (wave 4), positive affect was assessed in 2010-2011 (wave 5), and hs-CRP was assessed in 2012-2013 (wave 6). Path analysis adjusted for health-related variables including depressive symptoms, cardiovascular disease, BMI, smoking, alcohol consume, and drug intake showed a significant direct effect of sleep disturbance to positive affect; positive affect directly predicted hs-CRP. Lastly, an indirect effect between sleep disturbance to hs-CRP through the mediating role of positive affect emerged. The findings suggest that sleep onset and sleep maintenance difficulties may be associated with inflammation through the mediation of low positive affect. The clinical significance of the findings should be further explored.