A randomized controlled trial of Bikram yoga and aerobic exercise in the treatment of depression: Efficacy and underlying physiological and psychological mechanisms
Empirical interest in alternative treatment options for major depression has been on the rise, in part because of the shortcomings of conventional approaches. Despite a growing body of evidence supporting the use of various alternative treatments as either stand-alone or adjunctive therapies for depression (Ravindran et al., 2016), methodological limitations have plagued numerous individual trials. The current study aimed to examine the antidepressant effects of yoga in a study design that made several methodological improvements over previous trials. Bikram yoga was used as the yoga intervention because it is a standardized style of yoga that is readily available, thus lending itself well to subsequent replication. In addition to comparing its effects to those of no treatment, Bikram yoga was compared to an aerobic exercise intervention, as the latter has been well-supported for its mood-enhancing benefits and has even been incorporated into treatment guidelines for depression. Participants were 53 adult women who met diagnostic criteria for a depressive disorder. They were randomized to one of three 8-week conditions: Bikram yoga, aerobic exercise, or waitlist control. Results from an intention-to-treat analysis demonstrated response rates (i.e., >50% reduction on the Hamilton Rating Scale for Depression; HAM-D; Hamilton, 1960) of 61.1%, 60.0%, and 6.7%, respectively, for the yoga, exercise, and waitlist groups. When considering the sample of completers, 73.3% and 80.0% of participants in the yoga and exercise groups, respectively, achieved remission (i.e., no longer meeting diagnostic criteria for depression and HAM-D≤7) compared to only 8.3% in the waitlist condition. A secondary objective of this study was to examine relevant physiological and psychological variables that may underlie the antidepressant effects of Bikram yoga and aerobic exercise. Physiological variables included pre- to post-treatment changes in heart rate, blood pressure, and cortisol response to a psychological challenge test. Psychological variables were changes in level of perceived hassles, rumination, and mindfulness. Although these variables have been linked to depression and have also been found to be influenced by yoga and exercise, their role in mediating the antidepressant effects of yoga and exercise have gone largely unexplored. Rumination emerged as a significant mediator for both active treatment conditions. Acceptance, which is a component of mindfulness, also mediated the antidepressant effects of exercise. Possibly owing to methodological issues and extraneous factors that may have been inadequately controlled for, none of the physiological variables emerged as significant mediators. Suggestions for future research, including other potential mechanisms of action that may help better understand the mental health benefits of yoga and exercise, are highlighted.