Secret to old age: Happy nuns live longer according to research from the University of Kentucky - but why is that, and what can we learn to benefit from it?

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Three generations ago, 180 young women wrote brief essays describing why they wanted to become nuns. Years later, a team of psychological researchers came across these spiritual autobiographies in the convent's archives.

The researchers were seeking material that would confirm earlier studies hinting at a link between having a good vocabulary in youth and a low risk of Alzheimer's disease in old age. What they found was something even more amazing.

Although the young women had barely been out of college when they wrote their "why I want to be a nun" essays, the emotions expressed in these youthful writings were predictive of how long they would live: those who wrote the most upbeat autobiographies lived more than 10 years longer than those whose language was more neutral.

The results were particularly striking because all members of the convent lived similar lifestyles, eliminating many of the variables that normally make it difficult to interpret longevity studies.

"Once in a lifetime finding"

"It was a phenomenal finding," says Deborah Danner, a psychologist at the University of Kentucky in the U.S., who spearheaded the study. "A researcher gets a finding like that maybe once in a lifetime."

Because the autobiographies were written with the knowledge that they would be read by the mother superior, none were negative. "But even with that, you could get a feel for the person," says Danner. "Some had this glow about them."

Danner's study, however, offered no clues as to why positive emotions might have such strong life-extending effects.

Barbara Fredrickson, an associate professor of psychology at the University of Michigan, believes that part of the answer is something she calls the "undo effect." According to this theory, positive emotions help you live longer by shutting down the health-damaging side effects of negative ones.

Fredrickson's theory begins with the observation that negative emotions, like fear and anxiety, helped our ancestors survive by enhancing the flight-or-fight response to very real threats, such as predators or raiders from an enemy tribe. Even disgust plays a survival role, encouraging you to spit out food whose repulsive taste might mean that it is poisonous or spoiled.

Lingering cardiovascular effects

But when the crisis is gone, negative emotions produce lingering effects. One of these is excessive "cardiovascular reactivity."

Cardiovascular reactivity is a laboratory measure of cardiac excitability. "It's kind of like being jumpy," says Brooks Gump, an associate professor of psychology and stress researcher at the State University of New York in Oswego. Behaviourally, he says, it is related to excessive "vigilance," which is the state of being constantly on guard for potential dangers.

Not only is it physically draining to live in a perpetual state of high vigilance, but high cardiovascular reactivity has been linked to increased risk of heart attack.

Fredrickson believes that positive emotions work their magic by producing a rapid unwinding of pent-up tension, rapidly restoring the cardiovascular system to normal. People who quickly bounce back from stress often speed the process by deliberately harnessing such emotions as amusement, interest, excitement, and happiness, she says.

To test her theory, Fredrickson and co-worker Michele Tugade, now of Vassar College in Poughkeepsie, New York, told a group of student volunteers that they had only a few minutes to prepare a speech that would be critiqued by experts.

After letting the students get nervous about that for a few minutes, Fredrickson and Tugade then let them off the hook by telling them they wouldn't actually have to deliver their speeches. All the while, they monitored heart rates, blood pressures, and other factors related to cardiovascular reactivity. Afterward, they asked the students to report how they'd felt during the experiment.

Not surprisingly, everyone got nervous about the speech. But those who viewed the experiment with amusement, interest, and good-humoured excitement saw their heart rates return to normal much more quickly than those who were angry about being fooled.