Our findings extend prior work examining the therapeutic effects of yoga on emotional state. First, we found that beneficial effects not only address the biomedically defined symptoms of unipolar major depression, but yield improvements in a more broadly defined set of reports of mood state experience. Second, these effects are present at a session-by-session level as well as accruing over time. Third, pre-intervention autonomic differences were found between subjects who entered symptomatic remission with the yoga augmentation and those who did not, suggesting that it may be possible to consider prospectively which individuals with depression may benefit most from complementary yoga augmentation of anti-depressant medication.
The findings of the benefits of yoga for depressed patients in partial remission are consistent with previous studies of depressed patients (5
) using interventions that emphasize rhythmic breathing aspects of yoga. The Iyengar approach in the present study focused mainly on more active asanas and included only brief periods of relaxation and breathing exercises. Future studies will be needed to explore the relative importance of the various components of yoga practices (e.g. physical activity, attentional focus, specific postures) and the mechanisms by which they produce clinical benefits (44
). Iyengar yoga practice places a great deal of emphasis on ‘opening the chest’ as in the case of certain poses such as backbends, which may have direct effects on the circulation that may elevate mood and psychological well-being (8
A limitation of this study is the single-group outcome design with no placebo or other controls. As with many unblinded interventional studies, it is possible that the observed benefits in the present study may be related to other factors unrelated to our intervention, such as participation in a therapeutic program and expectations of benefit; of note, we found that the participants’ expectations assessed at intake were not correlated with symptomatic outcome. Regular participation in a social group is another such non-specific factor. No limitations were placed on socializing either immediately before or after each session or at other times. Future studies may incorporate explicit controls for this factor and should gather data on how much socializing took place and how it affects outcome. It is noteworthy that studies employing Iyengar yoga interventions for other conditions (cancer survivors, self-reported emotional distress) found beneficial effects for depression and mood as well as anxiety and physical well-being (45–47
). These studies included control conditions.
Our remission rate of 65% compares favorably with other CAM intervention studies: 43% using SAMe as an augmenter to anti-depressants (48
); 20% using omega-3 fatty acid (49
); 19% using folinic acid (50
). Coppen and Bailey (51
) added folic acid or placebo to fluoxetine, and found that 65% (folate) versus 48% (placebo) met ‘recovery’ criteria using a more liberal standard for remission (HAM ≤ 9) than in the present study. Using their criterion, the remission rate in our study is 77%. In a study of the effects of aerobic exercise as a monotherapy for depression, Dunn and colleagues (52
) found a 25% remission rate.
The attrition rate of 19% is lower than that occurs in exercise programs. Pollock (53
) reported that 50% of non-depressed individuals drop out of exercise programs within 6 months. In the report by Dunn et al
), 62% of the control condition using flexibility exercises dropped out. Only one of the many demographic, psychological and biological intake measures in the present study discriminated those who attended six or more classes from those who did not. Most of the latter stopped attending after one or two sessions; 6 out of the 37 who enrolled in the study attended no sessions at all. Reasons given for non-attendance were difficulties with transportation, location of the venue, parking and traffic congestion, even though all who were enrolled agreed to participate after they were informed in detail about the arrangements.
For all who completed the study, aside from clinical symptoms of depression, reductions were also observed in measures of anxiety, expression of anger, neurotic symptoms, limitations on usual role activities because of emotional difficulties, and LF-HRV. Thus, participation in yoga did not in effect target depression only but also affected psychological and biological processes indicative of improved mental health in general and more effective social behavior. LF-HRV reflects both sympathetic and parasympathetic innervation of the heart and is an indication of inadequate cardiac parasympathetic modulation (54
). The reduction in LF-HRV, however, was not coupled with an increase in HF-HRV, suggesting inadequate cardiac parasympathetic modulation. From these findings, we may speculate that yoga practice was beneficial in reducing stress responsivity, an effect which is generally associated with sympathetic nervous system activation. The pattern of HRV findings for those who achieved remission versus those who did not may seem counterintuitive in that it decreased in the former and increased in the latter. Those who achieved remission had higher levels of HRV at intake, and the observed opposite effect may reflect the phenomenon of regression to the mean.
We may speculate further on the reduction in HF-HRV observed in the patients who remitted. The capacity to suppress vagal influence appears to mediate attentional and emotional processes that allow an organism to optimally engage or cope with environment challenges (15
). Resting vagal influence and the capacity to suppress this influence have been found to be strongly related, but the precise distinction between these mechanisms and their concomitant behavioral processes is not yet clearly understood. This suggests the possibility that after yoga treatment, some patients with higher intake resting vagal tone became actively engaged in coping with their depression and improving their mental health. For the patients with initial lower resting vagal tone (non-remitters), yoga treatment may not increase vagal tone to a level needed sufficient to improve their condition. In these patients, it is possible that a longer period of treatment would be beneficial, and future experiments may explore this possibility.
We cannot exclude the possibility that a subject's breathing pattern may be affected by the specific yoga practices in this intervention and that such effects may be related to the HRV findings. Both rate and depth of respiration affect HRV (56
) and may have a general effect on the autonomic nervous system or an effect related to voluntary exercise efforts and that may be independent of vagal control of the heart. The latter may determine phasic respiration- but not tonic vagus-related changes in HF-HRV. One might see reductions in respiration rate associated with the focus on breathing in yoga practice, which would likely show up in increased HF-HRV, which was not the case for remitters. Further investigation is warranted on the effects of respiration and of other physiological pathways of yoga on mood and clinical condition.
The participants who remitted differed at intake in several ways from those who did not. They had less formal education, spent many more hours a week in regular exercise, and had higher levels of HF-HRV, lower levels of LF-HRV and higher BRS. The significance of the exercise and physiological effects is understandable and suggests that remitters were already disposed to an activity-based treatment and that from the standpoint of autonomic nervous system functioning they had a greater capacity for emotional regulation. Habitual exercise and physical activity appear to be beneficial for mood, depression and mental health in general and may facilitate remission in the treatment of depression (57
). The finding of less education for remitters may be in line with a greater disposition toward an activity-based rather than an educational or verbal therapy. In future studies, it may be advantageous to combine meditation or other mental approaches with the methods used in this study.
For further understanding of the differences between remitters and non-remitters, see which plots the means for six of the eight effects in and compares them with the means of the same measures obtained in 28 depressed and 28 matched healthy controls (30, discussed earlier). For these six measures, the calculations were exactly the same and directly comparable. It can be seen that for Education (Panel F) the NON-REMISS group had higher levels and the REMISS group lower levels compared with the ‘norms’ for depressed and healthy people. For exercise (Panel E), the NON-REMISS group stands out with many fewer hours of regular exercise. As to the measures of autonomic regulation (Panels A–D), it is apparent that the NON-REMISS participants differed most from the healthy group in all respects with lower BRS, higher LF/HF, lower HF-HRV and higher HR. It appears that exercise and education may have only additive or secondary influences on the differences between REMISS and NON-REMISS participants in baseline autonomic activity. In general, these comparisons support the conclusion that the non-remitters had reduced capacity for emotional regulation.
Differences between REMISS and NON-REMISS Participants compared with data on 28 depressed and 28 matched healthy individuals (means).
The mood data indicate that remitters tended to be in a better mood throughout the study, more positive and less negative. All participants felt better from before to after each yoga class: more positive, less negative, and more energetic; in fact, the non-remitters showed a greater improvement than the remitters as their initial and overall moods were less positive to begin with. Thus, mood improvements associated with yoga practice appear to be universal. How they affect depression in any one person must depend on other individual characteristics.
In conclusion, yoga appears to be a promising intervention for depression. It is cost-effective and easy to implement. Most importantly, yoga produces many beneficial emotional, psychological, behavioral and biological effects, as supported by observations in this study. The physiological methods are especially useful as they provide objective markers of the processes and effectiveness of the intervention. The methods and observations in this report may help guide further clinical research on the application of yoga in depression, with appropriate placebo control and comparison conditions, and in other mental health disorders, and in future research on the processes and mechanisms involved.