When Jenny Smith was 41 years old, her mental illness became so severe that she could barely walk or speak. After days of feeling wonderful one moment and hallucinating that spiders and bugs were crawling on her skin the next, she landed in the hospital.

Smith is a victim of , an illness characterized by oscillating feelings of elation and utter . And though she had tried 11 different medications for relief, some in combination, nothing seemed to work. Upon leaving the hospital, Smith was told that she could expect to be in and out of hospitals for the rest of her life. Soon after her release, Smith decided to learn hatha yoga, which incorporates specific postures, and pranayamas, deep abdominal breathing techniques that relax the body. As she practiced daily, Smith noticed that her —a symptom of , a disease that some bipolar disorder sufferers also contend with—were subsiding. She has since become a certified hatha yoga instructor, and with the help of only Paxil, an that she'd taken before without effect, Smith's pattern of severe seems to have ended. She even taught her 11-year-old daughter—who had experienced panic attacks since age 7—the simple breathing technique of inhaling to the count of four and exhaling to the count of eight; as a result, her daughter's panic attacks subsided.

Key to reaping hatha yoga's mental benefits is reducing and . To that end, Jon Cabot-Zinn, Ph.D., of the University of Massachusetts, developed the Stress Reduction and Relaxation Program (SRRP), a system that emphasizes , a meditation technique where practitioners observe their own mental process. SRRP has been the focus of several scientific studies in the last 20 years, and has been shown to significantly reduce anxiety and depression, and thus alleviate mental illness.

To date, the most persuasive evidence of the benefits of hatha yoga, and in particular pranayama, stems from research conducted by the National Institute of Mental Health and in India. New studies have shown a high success rate—up to 73 percent—for treating depression with sudharshan kriya, a pranayama technique taught in the U.S. as "The Healing Breath Technique." It involves breathing naturally through the nose, mouth closed, in three distinct rhythms.

According to Stephen Cope, a psychotherapist and author of Yoga and the Quest for the True Self, hatha yoga's postures improve mood by moving energy through places in the body where feelings of or are stored. "Hatha yoga is an accessible form of learning self-soothing," he says. "These blocked feelings can be released very quickly, [creating a] regular, systemic experience of well-being." Yoga students may also benefit from their relationship with the yoga instructor, Cope said, which can provide a "container" or a safe place for investigating, expressing and resolving . The instructor's encouraging and accepting words may also help students defeat self-limiting notions.

Not all mental health practitioners are convinced of yoga's healing powers, but many agree it can be helpful when combined with more traditional treatments. Zindel Segal, Ph.D., a University of Toronto psychiatry professor, recently studied SRRP when used in conjunction with cognitive . He asked 145 people who were at risk for depression to undergo cognitive therapy either alone or with the SRRP. Segal found that after eight weeks of treatment, those participants who received both types of therapy were much less likely to into depression. "This means that people can learn about their emotions not just by writing down their thoughts, which is what cognitive therapy is all about, but also by paying to the way their emotions are expressed in their bodies," he says. "Both approaches allow people to observe their experience without judgment, an important first step in stepping out of depression."

While yoga's therapeutic capabilities are still under scientific scrutiny, Smith isn't waiting for more proof. Having lost her grandmother to depression—she was one of many bipolar sufferers who take their own life due to the disease—Smith is determined not to let the disorder get the best of her. Since 1994, she has practiced and taught hatha yoga to depression sufferers—passing on what she believes has literally saved her life.