One of the obstacles to promoting the benefits of mind-body exercise to modern healthcare providers is the lack of solid research evidence to support the health claims. In recent years, this lack of evidence has stimulated many more researchers to conduct studies so that healthcare providers will have the confidence to recommend alternative treatments to patients who need help. In a review published in the online edition of the Journal of Affective Disorders (2005; doi:10.1016/j.jad.2005.08.013), U.K.-based researchers assessed all the studies available in English on the effectiveness of yoga for depression.
The reviewers found five randomized, controlled studies that met the initial criteria for credibility in the medical community. In a random sample, subjects are drawn from a population in which each subject has an equal probability of being selected. In a randomized study, people are placed in groups within the study (e.g., the control group and the exercise group) by chance. In a controlled study, the researchers compare a group of subjects who receive a particular intervention with another group of subjects who do not receive the intervention. Two other important study variables are whether or not a study has a large enough sample size to make the results meaningful and whether or not the measurable results are clinically significant in terms of their magnitude.
The five studies deemed credible had different sample sizes, used different types of yoga interventions and included individuals with depressive conditions ranging from mild to severe. While each study showed that yoga as a treatment had potentially beneficial effects, the fact that the studies varied so widely made it difficult to draw more concrete conclusions. No negative effects occurred except for fatigue and breathlessness in one study. The reviewers noted that yoga may not be a possible treatment for those with mobility issues.
The authors recommended that future studies in this field should focus on determining which types of yoga exercises are most beneficial and what levels of clinical depression respond most effectively to yoga as therapy. They also recommended that future studies on depression compare the effectiveness of yoga with the benefits of aerobic exercise and assess what results might be expected over both the short and the long term.