Time magazine recently made it a cover story. Physicians with names like Chopra, Dossey, and Benson have produced best-selling books on the topic and now frequent radio and TV talk shows. Foundations are offering big bucks to research the relationship, and energetic sociologists, psychologists, and health practitioners are vying for these funds.

What's the fuss all about? The relationship between faith and health. After many decades of neglect and even outright opposition, interest in the religion-health connection is now considered by many to be "medicine's last great frontier."

The Healing Power of Faith by Harold G. Koenig—the director of Duke University's prestigious Center for the Study of Religion/Spirituality and Health—is, therefore, most timely and informative.

As recently as a decade ago the religion-health connection was spurned. Skepticism, even hostility, toward any suggestion that there may be any health benefit from religious faith and practice prevailed. The public, never mind scientists, regarded it as the field of charlatans and quack faith healers.

But starting in the late 1980s a series of review articles began appearing in scientific journals that kept tabs on the growing evidence supporting religion's effects on health and mortality. The evidence, though sometimes conflicting and overinterpreted, is nevertheless convincing: rates of health and life span vary across religions and religious denominations, but on average, high levels of religious involvement are moderately associated with better health. These effects are not influenced by gender and are seen in different racial and ethnic groups and in samples from a wide range of religions.

This last point is crucial. Even when stringent statistical ...