After a busy, intense day of work at the clinic, I sometimes try to make an early evening yoga class at a nearby studio. It is a relief to empty my mind and focus on performing the poses the instructor sets forth.  

Over time, multiple studies have corroborated my experience of the benefits of yoga and meditation.  As Dr. Andrew Newberg of Thomas Jefferson University Hospital and Medical College writes, 

If you stay in a contemplative state for twenty minutes to an hour, your experiences will tend to feel more real, affecting your nervous system in ways that enhance physical and emotional health.  Antistress hormones and neurochemicals are released throughout the body, as well as pleasure-enhancing and depression-decreasing neurotransmitters like dopamine and serotonin.  Even ten to fifteen minutes of meditation appears to have significantly positive effects on cognition, relaxation, and psychological health, and it has been shown to reduce smoking and binge-drinking behavior.  

One of the pioneers in the study of the health benefits of meditation is Dr. Herbert Benson, Professor at Harvard Medical School.  His book, The Relaxation Response, is a classic and a great introduction to this field.