The Effects of an Online Yoga Nidra Meditation on Subjective Well-Being and Diurnal Salivary Cortisol: A Randomised Controlled Trial.

Yoga Nidra meditation has been increasingly examined in recent years for its potential to enhance psychological well-being. However, few studies have examined its biological effects-such as diurnal cortisol patterns particularly in larger samples using pre-post designs. The primary objective of this randomised controlled trial was to examine both the psychological (stress, anxiety, depression, rumination, sleep, satisfaction with life) and the biological effects (diurnal salivary cortisol) of Yoga Nidra. Participants were randomly assigned to 1 of 2 intervention groups (EG1: 11 min Yoga Nidra, n = 101; EG2: 30 min Yoga Nidra, n = 80), an active control group (AC: 10 min music, n = 74), or a waitlist control group (WC, n = 107). The intervention was delivered online via pre-recorded audio files and practiced ideally daily over 2 months. Significant improvements were observed for the 11-min Yoga Nidra group compared to the WC (effect sizes d = 0.08-0.16). Regular practice was associated with reductions in total cortisol and steeper diurnal slopes. Additionally, the short form significantly reduced depression compared to the AC (d = 0.13). The long form of Yoga Nidra showed an increase in acting with awareness (d = 0.10) compared to the short form. It also exceeded the effects of EG1 when compared to the AC and WC, including a flatter cortisol wake-up reaction. The importance of small effects through economic interventions for health-promoting behaviour is highlighted.