Yoga

What is it? A set of ritualized relaxation and breathing techniques, body positions, and movements derived from Indian philosophy, emphasizing harmony between mind, body, and spirit.

Supporters say: Some studies report that cancer patients who do yoga sleep better and have improved quality of life and lower stress. A study published last month concluded that an intensive yoga program improved the overall health of a small group of adults, reducing stress, anxiety, and depression. And yoga has been found to relieve symptoms of asthma, heart disease, depression, epilepsy, lower-back pain, fatigue, and headache.

Critics say: Evidence of such benefits is thin and mixed. A 2005 study found that yoga provided no significant benefit for those with mild-to-moderate asthma.

Risks: Small but real. Overstretching can cause injury or worsen an existing medical problem. Cases of stroke, blood vessel blockage, and damage to the eye, nerves, and spine have been reported.