Studies suggest that this practice modulates the stress response.
Since the 1970s, meditation and other stress-reduction techniques have been studied as possible treatments for depression and anxiety. One such practice, yoga, has received less attention in the medical literature, though it has become increasingly popular in recent decades. One national survey estimated, for example, that about 7.5% of U.S. adults had tried yoga at least once, and that nearly 4% practiced yoga in the previous year.
Yoga classes can vary from gentle and accommodating to strenuous and challenging; the choice of style tends to be based on physical ability and personal preference. Hatha yoga, the most common type of yoga practiced in the United States, combines three elements: physical poses, called asanas; controlled breathing practiced in conjunction with asanas; and a short period of deep relaxation or meditation.
Many of the studies evaluating yoga's therapeutic benefits have been small and poorly designed. However, a 2004 analysis found that, in recent decades, an increasing number have been randomized controlled trials — the most rigorous standard for proving efficacy.
Available reviews of a wide range of yoga practices suggest they can reduce the impact of exaggerated stress responses and may be helpful for both anxiety and depression. In this respect, yoga functions like other self-soothing techniques, such as meditation, relaxation, exercise, or even socializing with friends.
Taming the stress response
By reducing perceived stress and anxiety, yoga appears to modulate stress response systems. This, in turn, decreases physiological arousal — for example, reducing the heart rate, lowering blood pressure, and easing respiration. There is also evidence that yoga practices help increase heart rate variability, an indicator of the body's ability to respond to stress more flexibly.
A small but intriguing study further characterizes the effect of yoga on the stress response. In 2008, researchers at the University of Utah presented preliminary results from a study of varied participants' responses to pain. They note that people who have a poorly regulated response to stress are also more sensitive to pain. Their subjects were 12 experienced yoga practitioners, 14 people with fibromyalgia (a condition many researchers consider a stress-related illness that is characterized by hypersensitivity to pain), and 16 healthy volunteers.
When the three groups were subjected to more or less painful thumbnail pressure, the participants with fibromyalgia — as expected — perceived pain at lower pressure levels compared with the other subjects. Functional MRIs showed they also had the greatest activity in areas of the brain associated with the pain response. In contrast, the yoga practitioners had the highest pain tolerance and lowest pain-related brain activity during the MRI. The study underscores the value of techniques, such as yoga, that can help a person regulate their stress and, therefore, pain responses.
Improved mood and functioning
Questions remain about exactly how yoga works to improve mood, but preliminary evidence suggests its benefit is similar to that of exercise and relaxation techniques.
In a German study published in 2005, 24 women who described themselves as "emotionally distressed" took two 90-minute yoga classes a week for three months. Women in a control group maintained their normal activities and were asked not to begin an exercise or stress-reduction program during the study period.
Though not formally diagnosed with depression, all participants had experienced emotional distress for at least half of the previous 90 days. They were also one standard deviation above the population norm in scores for perceived stress (measured by the Cohen Perceived Stress Scale), anxiety (measured using the Spielberger State-Trait Anxiety Inventory), and depression (scored with the Profile of Mood States and the Center for Epidemiological Studies Depression Scale, or CES-D).