THURSDAY, Dec. 11 (HealthDayNews) -- Being fearful of the new and unknown may hasten your encounter with the greatest unknown of them all: death.

Researchers have found rats with neophobia, or fear of novelty, tend to die earlier than rodents who embraced life to its fullest.

To be fair, rats (and other animals, including humans) have good evolutionary reason not to leap before they look. Martha McClintock, co-author of a study appearing in this week's Proceedings of the National Academy of Sciences, describes neophobia as somewhere in line with vigilance, although it has also been linked with traits such as shyness, fearfulness and behavioral inhibition.

Most behaviors have their time and place. "Animals that run out into open areas to explore them without being vigilant risk being picked off by a predator. On the other hand, they have the benefit of finding new food resources or interacting with a group that might have a benefit," McClintock explains. "Everything's a trade-off. The animal who is hypervigilant and is scanning the environment before it moves out -- and when it does, hugging the walls -- will be less likely to be picked off by a predator. But it's not going to have the opportunity to explore."

McClintock and co-author Sonia Cavigelli conducted two experiments to see what else neophobic animals might be missing out on. Both studies used the relatively short-lived Norway rat.

The first study looked at adrenal activity in rodents with neophobia or with neophilia (those who weren't afraid of novelty).

The rats were classified as one or the other at 4 months of age. At 8 months of age, they were checked again to see if they exhibited the same behavioral traits. They did.

The rats were then placed in a new environment, one that minimized open spaces, which would induce fear in all the animals, not just the neophobic ones. The stress of this new space was roughly equivalent to low-level human stressors, such as being stuck in traffic or experiencing a problem with a computer.

Depending on their style, the animals either explored the space with enthusiasm or proceeded with slow, cautious movements. The rats in the latter category had a more rapid and higher adrenal response than their less phobic counterparts.

"We showed that we could detect this trait of neophobia before they were even weaned, and then that predicted how their adrenals reacted to being in a challenging situation like this in young adulthood and later on in middle adulthood," McClintock says.

The second study looked at life span in relation to neophobia and neophilia. Neophobic males died earlier than neophilic males. The median lifespan for the neophobic males was 599 days, versus 701 days for the neophilic males. None of the neophobic males lived beyond 840 days, while the maximum life span for neophilic males was 1,026 days, representing a 20 percent reduction in maximum life span. The causes of death tended to be the same in both groups: tumors or urinary tract blockage.

McClintock and Cavigelli don't yet know why this adrenal reaction might lead to a shorter life span. However, they do know that it is the fluctuation of the stress hormones and not so much the actual level that seems important.

"It was the going up and not coming down as fast," McClintock says. She likens it to hearing a sound in the middle of the night. Some people will wait and listen for a few minutes then fall back asleep. Others will worry for hours, alert for another noise.

"What we showed is that they recovered from that response more slowly," she adds. "We correlated that [with] an early death. It really suggests that we need to look at the effect of having a slow recovery to a stressor to being neophobic, where it happens over and over again on a daily basis."

And that is the other key element; that these hormonal changes were in response not to major life events, but to the equivalent of everyday nuisances.

"We're back into the same issue of, 'Does stress shorten one's life?'" says Dr. Ronald Kleinknecht, a professor of psychology and dean of the College of Humanities and Social Sciences at Western Washington University in Bellingham. "Various stress-related illnesses are going to affect quality of life. I'm not sure about longevity."

McClintock has already moved her research into humans. "We are trying to look at the effects of different types of psychological styles and social interactions on risk for disease," she says.

More information

The National Institute of Mental Health has more on anxiety disorders. Or check out the American Psychological Association for more on "painful shyness."

SOURCES: Martha McClintock, Ph.D., professor, psychology, and director, Institute for Mind and Biology, University of Chicago; Ronald Kleinknecht, Ph.D., professor, psychology, and dean, College of Humanities and Social Sciences, Western Washington University, Bellingham, Wash.; Dec. 8-12, 2003, Proceedings of the National Academy of Sciences

Last Updated: Dec-11-2003