One of the most striking scientific discoveries about religion in recent years is that going to church weekly is good for you. Religious attendance -- at least, religiosity -- boosts the immune system and decreases blood pressure. It may add as much as two to three years to your life. The reason for this is not entirely clear.
Social support is no doubt part of the story. At the evangelical churches I've studied as an anthropologist, people looked out for one another. They showed up with dinner when friends were sick and sat to talk with them when they were unhappy.
The help was sometimes surprisingly concrete. Perhaps a third of the church members belonged to small groups that met weekly to talk about the Bible and their lives. One evening, a young woman in a group I had joined began to cry. Her dentist had told her that she needed a $1,500 procedure, and she didn't have the money. To my amazement, our small group -- most of them students -- simply covered the cost, by anonymous donation.
A study conducted in North Carolina found that frequent churchgoers had larger social networks, with more contact, affection and social support among their friends than their unchurched counterparts. We know that social support is directly tied to better health.
Healthy behavior is no doubt another part. Certainly many churchgoers struggle with habits they would like to change, but on average regular church attendees drink less, smoke less, use fewer recreational drugs and are less sexually promiscuous than others.
That tallies with my own observations. At a church I studied in Southern California, the standard conversion story seemed to tell of finding God and never taking methamphetamine again. (One woman told me that while cooking her dose, she set off an explosion in her father's apartment and blew out his sliding glass doors. She told me, "I knew that God was trying to tell me I was going the wrong way.")
In my next church, I sat in a group listening to a woman talk about an addiction she could not break. I assumed she was talking about meth. It turned out that she thought she read too many novels.
There may be another factor. Any faith demands that you experience the world as more than just what is material and observable. This does not mean that God is imaginary, but that because God is immaterial, those of faith must use their imaginations to represent God. To know God in an evangelical church, you must experience what can only be imagined as real, and you must also experience it as good.
This is a skill that can be learned. Call it absorption: the capacity to be caught up in your imagination, in a way you enjoy.
What I saw in church as an anthropological observer was that people were encouraged to listen to God in their minds, but to pay attention only to those mental experiences that were in accord with what they took to be God's character, which was good. People were able to learn to experience God in this way, and those who experienced a loving God vividly were healthier -- at least, as judged by a standardized psychiatric scale. Increasingly, other studies bear out this observation that the capacity to imagine a loving God vividly leads to better health.
In one study, when God was experienced as remote or not loving, the more someone prayed, the more psychiatric distress she seemed to have; when God was experienced as close and intimate, the more someone prayed, the less ill he was.
In another study, at a private Christian college in southern California, the positive quality of an attachment to God significantly decreased stress and did so more effectively than the quality of the person's relationships with other people.
Eventually, this may teach us how to harness the "placebo" effect -- a terrible word, because it suggests an absence of intervention rather than the presence of a healing mechanism that depends neither on pharmaceuticals nor on surgery. We do not understand the placebo effect, but we know it is real. That is, we have increasingly better evidence that what anthropologists would call "symbolic healing" has real physical effects on the body. At the heart of some of these mysterious effects may be the capacity to trust that what can only be imagined may be real, and good.
But not everyone benefits from symbolic healing. The youngest son of famed pastor Rick Warren recently took his own life. We know few details, but the loss reminds us that to feel despair when you want to feel God's love can worsen the sense of alienation.
We urgently need more research on the relationship between mental illness and religion, not only so that we more intimately understand the ways in which they are linked and different, but to lower the shame for those who are religious and nonetheless need to reach out for other care.
T.M. Luhrmann is professor of anthropology at Stanford University and author of "When God Talks Back: Understanding the American Evangelical Relationship With God." She wrote this for The New York Times.