A growing mountain of evidence suggests that an upbeat, positive attitude could be the key to a long life. Some of the best scientific proof comes from the world of religion.
At the Franciscan Handmaids of Mary in New York, there can be an 80-year divide between the sisters who teach and the children in their classes. The age difference hardly matters. Many of the nuns are aging remarkably well, and doctors wonder if it's a matter of personality.
"I realize it is not how long you live but how intensely you live, in terms of appreciating your life and living life to the fullest," said Sister Loretta Theresa Richards.
Richards is 76, and doctors say her sense of purpose may be helping to keep her healthy. Studies show people who are busy, optimistic and have networks of friends tend to live longer. Involvement is good, not tiring.
"It does not wear you out," said Dr. David Bennett, director of the Rush Institute for Healthy Aging in Chicago. "It seems to keep everything working."
But why? How does the mind affect the body? Several studies have focused on nuns and monks because they have consistent lifestyles -- and are happy to help scientists in the cause of knowledge.
"I wake up in the morning and there is one prayer I say every day, and it carries me for the day," said Sister Anthony Marie Granger, 83.
Psychologists say there is an obvious need for negative emotions, such as fear, which tell us to run from danger.
But over the years, the stress hormones that result are bad for the heart and immune system. So it may be that positive emotions -- like optimism and serenity -- help your body recover from that stress.
Research has shown that people who meditate -- whether in prayer or under a doctor's guidance -- can lower their blood pressure.
"You can bring about biochemical, molecular, physiological changes in the body that are effective in treating stress conditions," said Dr. Herbert Benson, founding president of the Mind/Body Medical Institute and an associate professor at Harvard Medical School. Benson is the author of several best-selling books on what he calls "the relaxation response," a technique he says people can use daily to control stress.
Additional studies suggest that upbeat, stress-reducing traits appear at an early age. Some of the most striking findings have come, not from examining nuns in their later years, but from essays they wrote when they entered the convent in their 20s.
Those who were optimistic and had active minds back then, were the ones who aged best. On average, they lived 10 years longer than others.
The essays offer tantalizing clues, but researchers caution that, until recently, few people reached age 65. They died from infections, heart attacks and other causes, long before they had a chance to reach old age.
"You realize that this is really the first generation in the history of the world to get old," said Bennett. "We are really at the beginning of understanding aging."