Meditation may help ease anxiety and depression in certain patients, and in some cases the practice may be as effective as taking anti-depressant medications, said a study Monday. However, a review of scientific literature on mindfulness meditation published in the Journal of the American Medical Association found that the effects of meditation are limited. For instance, little or no evidence could be found of meditation's impact on positive mood, attention, substance use, eating habits, sleep and weight. Mindfulness meditation is a form of Buddhist self-awareness designed to focus attention -- not judgement-- to the moment at hand, the JAMA study said. "The evidence suggests that mindfulness meditation programs could help reduce anxiety, depression, and pain in some clinical populations," it said. "Thus, clinicians should be prepared to talk with their patients about the role that a meditation program could have in addressing psychological stress." The systematic review and meta-analysis was led by experts at Johns Hopkins University and included 47 randomized clinical trials with 3,515 participants. Of the thousands of studies the authors found on the topic, just three percent were scientifically rigorous enough to meet the criteria for inclusion in the JAMA review. Those that were reviewed found some small to moderate benefits, but lacked evidence of leading to better health. "Contrary to popular belief, the studies overall failed to show much benefit from meditation with regard to relief of suffering or improvement in overall health," said an accompanying commentary by Allan Goroll, a doctor at Harvard University. "With the important exception that mindfulness meditation provided a small but possibly meaningful degree of relief from psychological distress." The patients who received these benefits did not typically have full-blown anxiety or depression. Mindfulness meditation is usually practiced for about 30 minutes per day, and emphasizes acceptance of feelings and thoughts without judgment. It also requires body and mind relaxation. "A lot of people have this idea that meditation means sitting down and doing nothing," said the JAMA study's lead author Madhav Goyal, an assistant professor at the Johns Hopkins University School of Medicine. "But that's not true. Meditation is an active training of the mind to increase awareness, and different meditation programs approach this in different ways."