Taking it easy isn't the key to a long life, according to new research. Instead, it's the hard-working, prudent types who live the longest.

The findings come from an unprecedented study of 1,528 gifted children followed from the early 1920s until their deaths. The health and longevity part of the project has been under way for 20 years, with the results published in a new book, "The Longevity Project: Surprising Discoveries for Health and Long Life from the Landmark Eight-Decade Study" (Hudson Street Press, March 2011).

Among the findings: Conscientious, prudent people live a few years longer than carefree, happy-go-lucky sorts. Marriage lengthens life for men, but makes little difference for women, and social ties are longevity boosters for both genders. Hard workers who advanced in their careers and took on more responsibility were also more likely to live long, healthy lives.

"If you want to improve your health, you shouldn't just go on a joyride, but get involved in meaningful, productive kinds of things," study co-author Howard S. Friedman, a psychologist at the University of California, Riverside, told LiveScience.

Work harder, live longer

The children recruited for the study were identified by their teachers as the brightest students in their classes during the 1920s. At the time, Stanford professor Lewis Terman wanted to study whether intelligence led to later success in life. "There was a perception at the time that really intelligent children would grow up to be nerds and weird and maybe it was not such a good thing to be smart," Friedman said.

So he measured the children's personalities traits, recorded biographical and demographic information, and watched them throughout their lives. (For the record, the kids did show a lot of variation in how successful they were as adults. Future careers ranged from foreign reporter to atomic physicist and from trucker to secretary, Friedman said.)

Terman died in 1956. More than three decades later, Friedman and his co-author, psychologist Leslie Martin, picked up the research and turned it into a health study. The researchers combed through the data and collected new information on the participants, including death certificates from around the country.

"We know not only how long they lived but exactly what they died of," Friedman said.

The big surprise was that personality and character early on can predict health and longevity across decades, Friedman said. Dependable, prudent children on average avoided risks and eventually entered into stable relationships — a major boost for health, happiness and longevity. (Genes also matter for longevity.)

"Socioeconomic status is important, but what we found is it's probably the persistence and the dependability and the good social ties that really are the things that promote your health," Friedman said.

In many cases, Friedman said, participants made their own luck: A responsible personality helped them avoid even seemingly random stresses. The generation studied were the ones who ended up fighting in World War II, Friedman said. The most stressful combat position in that war was in the Pacific theater. When the researchers analyzed the WWII vets, they found a surprising correlation.

"It wasn't random who wound up there [in the Pacific]," Friedman said. "The most impulsive, least conscientious children were the ones who wound up fighting in the South Pacific."

Social ties that bind

The researchers also found that marriage and divorce had little effect on women's life spans, but singlehood was not kind to men. Men who got and stayed married were likely to live beyond age 70, but less than one-third of divorced men made it to that age. Men who never married outlived those who divorced, but not those who stayed married.

Part of the reason, Friedman said, is that the men's wives were their gateways to a social circle. With divorce, the men lost social support, which has been shown to be important for health and happiness. The researchers also found that men with what they termed "feminine" personality traits — a willingness to reach out to others and share feelings — outlived those with more closed-off, "masculine" traits. In the same way, more feminine women outlived more masculine women.

The researchers found that while pets can bring happiness, they were no substitute for friends in terms of improving health and well-being.

Generalizing the results

The conscientious, hard-working personality trait extends life by an average of two to three years, Friedman said, the equivalent to a 20 percent to 30 percent decreased risk of early death. That's "about the effect size of things we normally pay attention to, like systolic blood pressure," he said, referring to the life span advantage of a healthy blood pressure.

The participants were mostly white and middle class, but Friedman said the results are likely to generalize to other groups. Other studies have found similar results in other populations, including a large analysis of multiple studies done by Friedman that looked at about 8,900 people from the United States, Canada, Germany, Norway, Japan and Sweden.

The researchers continue to analyze the data from the Terman study group, and plan to branch out to include another group of people first studied as children in Hawaii in the 1950s.

Friedman said that although personality seems to affect longevity, the class clowns of today shouldn't fear an early death. People can change, he said, and those who bolster their work ethic later in life see the benefits in their health and longevity. For Friedman himself, the study has prompted at least one change.

"The whole idea of retirement has a really different meaning to me now," he said.

This article was reprinted with permission from LiveScience.

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