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 how stressed we are (and feel)? Various studies have reported that yoga may decrease self-reported stress levels, as well as those of stress biomarkers; however, evidence for these claims remains inconclusive, with results even more ambiguous for yoga styles with a focus on physical postures. In a randomized controlled trial with 98 participants, we therefore intended to answer the question if an eight-week Hatha Yoga intervention (3×/week or more, 60 min), compared to a waitlisted control group, decreased levels of diurnal salivary cortisol, salivary alpha-amylase, and subjective momentary stress. To ensure concomitant assessment of self-reported and biological measures in an ecologically valid setting, and to capture the diurnal profile of cortisol and alpha-amylase, we utilized an ecological momentary assessment approach, asking participants to report their momentary stress levels on a visual analogue scale five times a day together with self-collecting salivary biomarkers. While subjective momentary stress decreased significantly due to the intervention, we did not observe a change in diurnal salivary cortisol or alpha-amylase levels. Our results give room for several possible explanations: Participants may have learned to better cope with stress as a consequence of the intervention, but this may have left diurnal levels of stress biomarkers unaffected or, at least, diurnal sCort and sAA levels did not reflect this change. Alternatively, participants may have reported reductions in stress to indicate positive effects of the intervention, potentially influenced by a favorable disposition towards yoga, thus reflecting a self-reporting bias. Our findings contribute to a better understanding of the effects of distinct yoga interventions, showing their potential to serve as low-risk stress mitigation tools.