Men who are hostile and given to fits of anger and depression may be harming their immune systems and putting themselves at risk for heart disease, as well as type 2 diabetes and high blood pressure.

These are the findings of a new study in which Steven Boyle, Ph.D., of Duke University Medical Center and colleagues studied 313 male Vietnam veterans who were part of a larger 20-year study on the effects of Agent Orange.

To begin with, the veterans underwent a standard psychological test used to assess hostility, depression and anger. They then took a series of blood tests between 1992 and 2002. Researchers measured two immune system proteins, C3 and C4, which are markers of inflammation. Inflammation is the body's response to injury or infection. Changes in C3 and C4 are associated with a number of diseases, including coronary artery disease and diabetes.

Men who showed the highest level of hostility, depressive symptoms and anger had a 7.1 percent increase in their C3 levels, while men with low levels of these attributes showed no change over the 10-year study period.

The researchers allowed for other risk factors for higher C3 levels such as smoking, age, race, alcohol use and body mass index. They did not find significant increases in C4 levels.

"We showed positives associations between psychological attributes and 10-year changes in C3 among initially healthy middle-aged males," the researchers write.

"Hostile, depressed and angry people see the world around them in a different way, and sometimes they see it as them against the world," said study co-author Edward Suarez, Ph.D. "That kind of lifestyle often leads to greater stress and possibly changes in the way the body functions that could lead to disease."

The study appears in the August 2007 issue of the journal Brain, Behavior, and Immunity.