A Johns Hopkins review of 47 clinical trials encompassing 3,515 participants found that 30 minutes of daily meditation may improve symptoms of anxiety and depression. The review covered studies involving meditation and various health issues including depression, anxiety, stress, insomnia, substance use, diabetes, heart disease, cancer, and chronic pain.
Researchers found moderate evidence of improvement in anxiety, depression, and pain after what was typically an eight-week mindfulness meditation training program. In studies that followed participants for six months, the improvements typically continued. The researchers stated that meditation programs appear to have an effect above and beyond the placebo.
Half an hour. That is the daily investment the evidence supports. Published in JAMA by Johns Hopkins Medicine.
Source: Yoga Research: Mental Health & Trauma on ashtanga.tech. Original research.

