Epidemiologic studies have consistently shown an association of long sleep (≥8 hr) with mortality and multiple morbidities. However, there has been little experimental investigation of the effects of sleep extension. The aim of this study was to examine the effects of time in bed (TIB) extension, on depression, anxiety, sleepiness, and systemic inflammation. Following baseline, 14 healthy sleepers (31.79±10.94 years) were randomized to one of two one-week treatments: (1) a TIB extension treatment involving a fixed sleep schedule in which TIB was increased by 3 hours/night compared with the participants' median baseline TIB; (2) a control treatment involving a fixed schedule in which TIB was the same as the participants' median baseline TIB. Actigraphic recording of sleep was assessed throughout both weeks. Self-reported depression, state anxiety, sleepiness, and sleep quality, as well as blood pressure, and inflammation were assessed at baseline and following the treatment week. Compared with baseline, TIB increased by 127.12±3.92 min and total sleep time increased by 119.88±18.52 min during TIB extension, but decreased slightly in the control treatment. Depression was elevated more following TIB extension (effect size (ES)=-0.86) vs. control (ES=-0.50). Interleukin-6 levels increased by 2-fold following TIB extension (ES=-0.65), but did not change following the control treatment. Sleepiness increased after TIB extension, but decreased after the control treatment. The results revealed negative effects of TIB extension on mood and inflammation. Larger-scale studies involving more prolonged, but less profound sleep extension, are warranted.
Keywords: Depression; Healthy adults; Inflammation; Sleep extension.