cognitive-behavioral therapy; depression; duration; health; insomnia; metaanalysis; outcomes; Sleep; Transcutaneous vagal nerve stimulation; tVNS; vagus nerve; well

Short sleep duration and poor sleep quality are common in the general population. This study tested if a 2-week course of daily transcutaneous vagal nerve stimulation (tVNS) improves sleep in community-dwelling adults. Participants were n = 68 men and women aged 18-75 years randomised into four groups: early and sham tVNS and late and sham tVNS. Early groups underwent daily 4 h stimulation between Day 0 and 13, while late groups underwent daily 4 h stimulation between Day 14 and 28. tVNS was performed with transcutaneous electrical nerve stimulation (TENS) on the left tragus, and sham tVNS (control conditions) was applied on the left earlobe. Sleep was measured with the Pittsburgh Sleep Quality Index. Analysis of prespecified contrasts (C), based on linear mixed modelling, revealed that for tVNS there were significant improvements in global sleep scores over time between Day 0 and Day 13 in the early stimulation phase (C =-1.90; 95% CI =-2.87 to-0.94), and between Day 14 and Day 28 in the late phase (C =-0.87; 95% CI =-1.41 to-0.32). No such differences were found under sham tVNS (applied early or late). However, global sleep scores showed no significant improvement under tVNS when compared against control groups during both the early (chi(2) = 0.83, p = 0.36), or late stimulation phase (chi(2) = 0.24, p = 0.63). We showed that two weeks of tVNS improves global sleep scores, but the change in sleep was not significantly different to control groups. Further studies are warranted to test the utility of tVNS in alleviating sleep complains in community-dwelling adults.