OK, all you grumps and grouches out there--it may be time for some self-reflection and a change of heart, because your bad attitude could be killing you.

A new study finds that unpleasant people have a higher risk of stroke.

In fact, the most disagreeable people are more likely to have actual physical differences in the lining of the carotid artery, putting them at risk for this life- altering, debilitating and possibly even deadly event.

Researchers at the National Institute on Aging in Bethesda, Maryland, examined data from an ongoing study of 5,614 residents of Sardinia, an island off Italy known for its beautiful beaches.

You might think it would be hard to be disagreeable while living in a Mediterranean paradise, but an assessment of six character traits found that some of these people managed to be real jerks despite all that wine, cheese and sun.

And ultrasound measurements of their carotid arteries found that the most hostile and antagonistic of the bunch--those who rated in the lowest 10 percent in the agreeability assessment--were 40 percent more likely to have thickening in the lining of the carotid artery.

These nastier folks also had a higher risk of increased thickening during a three-year follow-up period, according to the study published in Hypertension.

What's more, this difference remained even after the researchers factored in other possible causes--such lifestyle-related risk factors. The study indicates that having a highly aggressive personality may be as much of a stroke risk factor as smoking, high LDL ("bad") cholesterol or high blood pressure.

And while many people associate overly aggressive behavior with men, the researchers say aggressive women were more likely to experience thicker artery linings.

On the other hand, men tend to have thicker artery walls to begin with, so maybe there's some truth to that old feminist rallying cry: Men are jerks.

The researchers behind the new study say not all unpleasant traits are equally deadly--because the highest risk came from those who were specifically manipulative and aggressive.

If that sounds like anyone you know, you might want to warn them that it's time to change their ways, or maybe you'll be visiting them in the emergency room one of these days.

Of course, a true jerk won't listen anyway--and that emergency room might turn out to be a very lonely place.