Evidence

Clinical Research on the Health Benefits of Meditation

Several hundred studies have been conducted on meditation and its health benefits for a variety of conditions, including heart disease, cholesterol, high blood pressure, insomnia, chronic pain, cancer, and immunity. Research also indicates benefits in mental health, memory, concentration, and productivity. Some of the more significant of these studies are listed below:

Heart disease

1) Meditation lowers blood pressure in people who are normal to moderately hypertensive. This finding has been replicated in more than nineteen studies, some of which have shown systolic reductions among subjects of 25 mmHg or more.
Murphy and Donovan, The Physical and Psychological Effects of Meditation, Institute of Noetic Sciences, 1997

2) Stress management appears to be as beneficial as aerobic exercise in preventing major cardiac events. A group receiving standard care turned out to have the most cardiac events, such as heart attacks, open-heart surgery, and angioplasty. The group that studied stress management had fewer problems - equal to that of the aerobics group.
Blumenthal, American Journal of Cardiology, 89 (January, 2002)

3) Twenty-eight people with high levels of blocked arteries and high risk of heart attack practiced a program of meditation, yoga, a low-fat vegetarian diet, and exercise. A control group received conventional medical care endorsed by the AMA. In one year, most of the experimental group reported that their chest pains had virtually disappeared; in 82% of the patients, arterial clogging had reversed. The control group experienced an increase in chest pain and arterial blockage. Subsequent studies indicate that stress-reduction may be the most significant factor. 
Ornish, The Lancet 336 (July, 1990)

4) Meditation significantly increases circulation. Forearm blood flow increased in novice meditators by 30%. Frontal cerebral blood flow increased an average of 65% in experienced meditators, and remained elevated afterwards, with brief increases of up to 100 to 200%.
Murphy and Donovan, The Physical and Psychological Effects of Meditation, Institute of Noetic Sciences (1997)

Insomnia

5) 75% of long-term insomniacs who have been trained in relaxation, meditation, and simple lifestyle changes can fall asleep within 20 minutes of going to bed.
Jacobs, Harvard Medical, Say Goodnight To Insomnia, Owl Books (1999)

Chronic pain

6) Those trained in meditation were able to reduce chronic pain by more than 50%. This gain was maintained even 4 years after the initial training. 
Kabat-Zinn, Clinical Journal of Pain 2 (1986)

7) Meditation and relaxation therapies are effective in treating chronic pain, and can markedly ease the pain of low back problems, arthritis, and headaches. 
National Institutes of Health (NIH), JAMA 276 (4) (1996)

Hospitalisation

8) In a study of health insurance statistics, meditators showed hospitalization rates 87% less than non-meditators for heart disease, 55% less for benign and malignant tumors, 30% less for infectious diseases, and 50% less for out-patient doctor visits.
Orme-Johnson, Psychosomatic Medicine 49 (1987)

9) Surgery patients who learned simple relaxation and meditation techniques stayed in the hospital an average of 1.5 days fewer than those in a control group. Results include faster recovery from surgery, fewer complications, and reduced postsurgical pains. Findings were consistent in 191 independent studies.
Devine, University of Wisconsin, School of Nursing, Patient Education and Counseling 19 (1992)

Mental health

10) A group of inner-city residents suffering from chronic pain, anxiety, depression, diabetes, and hypertension were trained in meditation. They experienced a 50% reduction in overall psychiatric symptoms, a 70% decrease in anxiety, and a 44% reduction in symptoms.
Roth and Creaser, Nurse Practitioner, 22 (3) (1997)

11) Meditation helped chronically depressed patients to reduce their relapse rate by half.
Journal of Consulting and Clinical Psychology 68 (2000)

Aging

12) Those practicing meditation for more than five years were physiologically 12 years younger than their chronological age, measured by reduction of blood pressure, better near-point vision, and auditory discrimination. Short-term meditators were physiologically five years younger than their chronological age.
International Journal of Neuroscience 16 (1982)

Children's health

13) Middle school students exposed to relaxation and meditation techniques over a three year period scored higher on work habits, cooperation, attendance and had significantly higher GPA's than non-meditating students.
Benson, Journal of Research and Development in Education 33 (3) (2000)

14) Forty-eight children who participated in a 6-week meditation program showed significant improvements in behavior, self-esteem, and relationship quality, with an average 35% improvement in ADHD symptoms. Of 31 children taking medication for their ADHD. 11 were able to reduce their medications.
Harrison, Clinical Child Psychology and Psychiatry 9 (4) (October, 2004)

Addiction

15) Meditative self-awareness can reduce binge overeating. In a study of overweight women, meditation training and awareness practice while eating (slowly savoring the flavor of a piece of cheese, being aware of how much is enough), reduced eating binges from an average of 4 per week to 1.5 per week.
Kristeller and Hallett, Journal of Health Psychology 4 (1999)

16) Meditation produced a larger reduction in tobacco, alcohol, and illicit drug use than standard substance abuse treatments or prevention programs. Whereas effects of conventional programs normally decrease significantly by three months, effects of meditation on total abstinence from tobacco, alcohol, and illicit drugs ranged from 50% to 89% over 18 to 22 months.
Alexander, Alcoholism Treatment Quarterly 11 (1994)

Productivity

17) Stress reduction significantly reduces medical errors. Twenty-two hospitals that implemented a stress prevention program experienced a 50% drop in medical errors and a 70% reduction in malpractice claims, compared to a control group of twenty-two hospitals, which showed no change in errors or claims.
Jones, Journal of Applied Psychology 73 (4) (1988)

18) Technology workers at a small Wisconsin company reported high stress and unhappiness with their jobs. Scans confirmed high levels of right-brain activity.* After eight weeks of meditation practice, activity in the left side of the brains increased significantly. Workers reported feeling happier, with a renewed sense of enthusiasm for life and work. The control group showed no change. At the end of the 8 weeks, both groups received flu shots to test immune responses. The meditators developed more antibodies against the flu virus than the non-meditators. Those with the strongest immune response had the highest levels of left-sided brain activity.

*Brain scans show that meditation shifts activity in the prefrontal cortex from the right hemisphere to the left. People who have a negative disposition tend to be right-prefrontal oriented; left-prefrontals have more enthusiasms, more interests, relax more, and tend to be happier.
Davidson and Kabat-Zinn, Psychosomatic Medicine 65 (2003)