Research has shown that hostile people may be courting heart attacks, but new work shows that nervous, withdrawn people also may have reason to worry.

"What we're seeing is over and beyond what can be explained by blood pressure, obesity, cholesterol, age, cigarette smoking, blood sugar levels and other cardiovascular risk factors," said Dr. Biing-Jiun Shen, a psychology professor at the University of Southern California.

Shen said the effect is stronger than those for depression, anger or hostility.

His team studied 735 men who started out in 1986 in good health, and looked at things such as doubts and obessive thoughts; introversion and discomfort in social situations; phobias; and feelings of tension when under stress. They were evaluated every three years.

The men with the highest anxiety scores -- the top 15 percent -- had a 30 to 40 percent greater chance of having a heart attack during the study.

"The good thing about anxiety is that it's very treatable," said Shen. "If someone is highly anxious -- if they're suffering from panic attacks or social phobia or constant worry -- we recommend therapy. ... This is one more reason to seek help."