In a meta-analysis of cross-sectional studies examining non-depressed participants, sleep disturbances (poor sleep quality, long sleep duration [> 8 hours], and insomnia complaints) were associated with higher levels of both CRP and IL-6 [47], suggesting that various indicators of sleep disturbances can be associated with higher levels of inflammation in the absence of comorbid depression. Here, CRP is linked to depressive symptom measurement.