These results have been ascribed to the rules imposed on believers and to the social support they receive from fellow worshipers, but these external factors didn’t account for all the benefits. In the new paper, the Miami psychologists surveyed the literature to test the proposition that religion gives people internal strength.

“We simply asked if there was good evidence that people who are more religious have more self-control,” Dr. McCullough. “For a long time it wasn’t cool for social scientists to study religion, but some researchers were quietly chugging along for decades. When you add it all up, it turns out there are remarkably consistent findings that religiosity correlates with higher self-control.”

As early as the 1920s, researchers found that students who spent more time in Sunday school did better at laboratory tests measuring their self-discipline. Subsequent studies showed that religiously devout children were rated relatively low in impulsiveness by both parents and teachers, and that religiosity repeatedly correlated with higher self-control among adults. Devout people were found to be more likely than others to wear seat belts, go to the dentist and take vitamins.

But which came first, the religious devotion or the self-control? It takes self-discipline to sit through Sunday school or services at a temple or mosque, so people who start out with low self-control are presumably less likely to keep attending. But even after taking that self-selection bias into account, Dr. McCullough said there is still reason to believe that religion has a strong influence.

“Brain-scan studies have shown that when people pray or meditate, there’s a lot of activity in two parts of brain that are important for self-regulation and control of attention and emotion,” he said. “The rituals that religions have been encouraging for thousands of years seem to be a kind of anaerobic workout for self-control.”