Middle-age and older people who are highly stressed, have depression or who are perhaps even just cynical may be at increased risk of stroke, according to new research.

In the study, more than 6,700 healthy adults ages 45 to 84 completed questionnaires about their stress levels, depressive symptoms, feelings of anger, and hostility, which is a measure of holding cynical views about other people. The researchers then followed the participants for eight to 11 years, and looked at the relationship between these psychological factors and people's risk of having a stroke.

"There's such a focus on traditional risk factors — cholesterol levels, blood pressure, smoking and so forth. And those are all very important, but studies like this one show that psychological characteristics are equally important," said study researcher Susan Everson-Rose, an associate professor of medicine at the University of Minnesota in Minneapolis.

By the end of the study period, about 200 strokes had occurred. The researchers found that people with high levels of cynicism were more than twice as likely to have a stroke compared with their less cynical counterparts.

The researchers also found that people with the most symptoms of depression were 86 percent more likely to have a stroke during the study compared with people with the lowest number of depressive symptoms. Similarly, people who had chronic stress were 59 percent more likely to have a stroke compared to stress-free participants. [8 Tips for Healthy Aging]

The researchers noted they did not find a link between feelings of anger and increased risk of stroke.

The results of the study held even when researchers accounted for known risk factors of stroke, including age, race, sex and health behaviors, according to the study published today (July 10) in the journal Stroke.

The findings suggest that psychological well-being, which has already been linked to heart health, also plays a role in stroke risk, the researchers said.

A stroke happens when the brain does not receive enough blood, due to the rupture of a blood vessel or a blockage in the arteries. In the United States, stroke is the fourth leading cause of death, and is a major cause of adult disability. About 800,000 people in the United States have a stroke each year, according to the Centers for Disease Control and Prevention.

It's not entirely clear how stress and negative emotions affect the heart or the brain, but emotions are shown to have metabolic, hormonal and immune effects, the researchers said. People who experience higher levels of stress, depressive symptoms or hostility could experience changes in their nervous or hormonal systems that, in turn, increase their risk for stroke, the researchers said.

It is also possible that negative emotions affect health by inducing inflammation, the researchers said.

People with high levels of stress and depression are more likely to engage in unhealthy behaviors such as smoking and excessive drinking, which would increase their stroke risk, the researchers said. But in this study, the results didn't change when the researchers accounted for people's smoking and drinking habits, or their physical activity and blood pressure.

Email Bahar Gholipour . Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.