Hatha yoga reduces momentary stress but does not impact diurnal profiles of salivary cortisol and alpha-amylase: A randomized controlled trial

Does the practice of yoga impact stress? Various studies have suggested that yoga may reduce both self-reported stress and stress biomarkers, but the evidence for such claims remains inconclusive, especially for yoga styles with a focus on physical postures. In a randomized controlled trial with 98 participants, we therefore examined whether an eight-week Hatha yoga intervention (60 min, 3×/week or more) led to reduced levels of diurnal salivary cortisol (sCort), salivary alpha-amylase (sAA), and subjective momentary stress as compared to a waitlist control group. To ensure the concomitant assessment of self-report and biological measures in an ecologically valid setting, and to capture the diurnal profile of cortisol and alpha-amylase, we employed an ecological momentary assessment approach. Five times per day, participants reported their momentary stress levels on a visual analogue scale and collected saliva samples for the assessment of salivary biomarkers. The intervention led to a significant reduction of subjective momentary stress but there was no change in diurnal sCort or sAA levels. There are several potential explanations for these findings: The intervention may have helped participants to cope better with stress while leaving diurnal levels of stress biomarkers unaffected, or the change may at least not have been reflected in sCort and sAA. Alternatively, there may have been a self-report bias, insofar as a favorable disposition towards yoga may have led participants to report reductions in stress in order to indicate positive effects of the intervention. Our findings contribute to a better understanding of the effects of distinct yoga interventions, demonstrating their potential to serve as low-risk stress relief tools.