Background: Yoga is a representative mind-body therapy of complementary and alternative medicine. In Japan, yoga is practiced widely to promote health, but yoga-associated adverse events have also been reported. To date, the frequencies and characteristics of yoga-related adverse events have not been elucidated. This study was conducted to elucidate the frequencies and characteristics of adverse events of yoga performed in classes and the risk factors of such events. Methods: The subjects were 2508 people taking yoga classes and 271 yoga therapists conducting the classes. A survey for yoga class attendees was performed on adverse events that occurred during a yoga class on the survey day. A survey for yoga therapists was performed on adverse events that the therapists had observed in their students to date. Adverse events were defined as undesirable symptoms or responses that occurred during a yoga class. Results: Among 2508 yoga class attendees, 1343 (53.5%) had chronic diseases and 1063 (42.3%) were receiving medication at hospitals. There were 687 class attendees (27.8%) who reported some type of undesirable symptoms after taking a yoga class. Musculoskeletal symptoms such as myalgia were the most common symptoms, involving 297 cases, followed by neurological symptoms and respiratory symptoms. Most adverse events (63.8%) were mild and did not interfere with class participation. The risk factors for adverse events were examined, and the odds ratios for adverse events were significantly higher in attendees with chronic disease, poor physical condition on the survey day, or a feeling that the class was physically and mentally stressful. In particular, the occurrence of severe adverse events that interfered with subsequent yoga practice was high among elderly participants (70 years or older) and those with chronic musculoskeletal diseases. Conclusions: The results of this large-scale survey demonstrated that approximately 30% of yoga class attendees had experienced some type of adverse event. Although the majority had mild symptoms, the survey results indicated that attendees with chronic diseases were more likely to experience adverse events associated with their disease. Therefore, special attention is necessary when yoga is introduced to patients with stress-related, chronic diseases.
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