Guy looking in the mirror(Photo: Courtesy of Men's Health)

Researchers found that men who scored high on a psychological scale of narcissistic behavior had levels of the stress hormone cortisol that were three times higher than men who scored low in narcissism. "So we can infer that narcissistic guys are under more constant stress than the average person," says study author Sara Konrath, Ph.D., a psychology professor at Michigan.

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Perpetually high cortisol levels could lead to an increased risk of cardiovascular disease and heart attacks, Konrath says. What's more, too much stress also makes it tougher to survive cancer, diabetes, and a number of other chronic diseases. Although no one has studied a direct connection between narcissism and health consequences, a series of studies in the 1980s found that people who used "I" most frequently while speaking also had the highest risk of heart disease.

Konrath believes that narcissists stress themselves out by constantly bridging the mental gap between their own unrealistically high confidence and their actual less-than-stellar performance. "It's hard to keep up that image of themselves when reality keeps slapping them in the face," she says.

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While a healthy amount of self-esteem is always nice to have, too much of a good thing can turn ugly. In narcissists, confidence comes along with a lack of empathy toward others and a tendency toward aggressive behavior, particularly when facing criticism, Konrath says. In her study, those worst aspects of narcissism were also most associated with high cortisol levels.

If you think you're in love with yourself, then you probably are. Konrath is working on a one-question test for narcissism that simply asks whether someone thinks they're a narcissist. So far, just agreeing with that statement lines up well with the standard 40-question psychological test, although the results are still preliminary.

In the meantime, buddy up. Konrath recommends spending time with people who share a common interest -- maybe join a running club, or meet up with fellow alumni to watch your college hoops team. In a separate study, she found that focusing on a shared trait makes narcissists less pushy and helps them to care more about others.

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