The number of Americans who attend religious services at least once a week jumped nearly three points to 27.5 percent during the two years ended in 2004, according to statistics to be released this week by the University of Chicago's National Opinion Research Center.

This leap could be good news for the nation's health. A growing body of scientific evidence shows that Americans who attend religious services at least once a week enjoy better-than-average health and lower rates of illness, including depression. Perhaps most important, the studies show that weekly attendance confers a significant reduction in mortality risk over a given period of time.

These studies have received almost no attention, in part because there is skepticism among many medical scientists about their validity, as Dr. Lynda Powell can attest. A professor of preventive medicine at Chicago's Rush University Medical Center, Powell was a nonchurchgoer who was very suspicious of such studies. Then in 2001, the National Institutes of Health asked her to lead a three-scientist panel that would review the mounting pile of medical literature purporting to link religion to health.

The panel found scant evidence of the benefit of religion on illness, and found that patients who used religion to cope fared slightly worse than those who didn't. "Religious people who become upset by the belief that God has abandoned them or who become dependent on their faith, rather than their medical treatment, for recovery may inadvertently subvert the success of their recovery," concluded the panel's report, which was published in the January 2003 journal American Psychologist.

But the panel's examination of studies showing the effect of church attendance on health reached an altogether different conclusion. As Powell, who is continuing to research this issue, puts it: "After seeing the data, I think I should go to church."

The panel reported that the studies showed a 25 percent lower mortality rate for those who attend religious services at least weekly. Each study covered a different period of time. But generally speaking, that means that during any period in which there were 100 deaths among those who don't attend weekly, only 75 weekly attendees would die, even though both groups on paper seemed at equal risk for death, Powell says.