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The value of social support is the easiest to demonstrate. Religion, after all, derives from the Latin religio, meaning "to bind together"--linking individuals to family and ancestors, friends and community, clergy and congregation. A person with strong social connections could get similar benefits from family meals or knitting circles, McCullough allows, but "people who are religious may just get more of it." Plus there's the added layer of spiritual support. "If you believe there's a God watching out for you, that's profoundly comforting," he says. "It's the grand-scale equivalent of thinking, If I can't pay my rent at the end of the month, my dad will help."
Doing good works through acts of charity or prayer and meditation provides another sense of connection to community for many believers. That is a key factor in Buddhism's capacity to foster happiness, says clinical psychologist Lorne Ladner, who has written on the topic. "A person might emulate the Buddha by imagining he's breathing in the suffering of others and breathing out energy to heal them," Ladner explains. "You literally breathe in sadness and exhale joy. This doesn't magically alleviate people's suffering, but the practice does help a person develop a strong sense of compassion, and compassion has been linked to happiness."
So has the sense of purpose and grand design that religious faith provides. Studies show that those who believe in life after death, for example, are happier than those who do not. "Religion provides a unifying narrative that may be difficult to come by elsewhere in society," says sociologist Christopher Ellison of the University of Texas at Austin.
It's not just what religion gives but what it takes away. "The 'thou shalt nots'--no adultery, no drugs and so on--keep people from getting addicted or otherwise increasing their level of stress," says Koenig. (That is, if they follow the rules.) The strictures of religion may simplify life for adherents, and that can be a huge relief. "One of the benefits of observance is that it helps people solve the freedom-of-choice problem," says Barry Schwartz, a psychology professor at Swarthmore College and the author of The Paradox of Choice: Why More Is Less. "This wasn't always a blessing. In a more restrictive society, people may not have embraced being told what to do. But in a world in which anything is possible, religion can provide guidelines to those who are overwhelmed by an abundance of options."