New York ? Americans who said they became anxious and stressed after the Sept. 11 terrorist attacks – some just from watching the collapse of the twin towers on television – reported higher rates of heart disease up to three years later, researchers said.

While several studies have found high rates of post-traumatic stress disorder and anxiety in first responders or attack survivors, most of the nearly 2,000 people randomly selected nationwide for the study had no direct connection to Sept. 11.

The research showed that before Sept. 11, about 22 percent of the participants reported they had heart ailments. Three years after the attacks, about 31 percent of them said they had developed heart problems.

People who said they were acutely stressed by the attacks were more than twice as likely to have high blood pressure one year after the attacks and more than three times as likely to have heart problems two years after the attacks, according to the study reported in January’s issue of the journal Archives of General Psychiatry.

The findings document the physical consequences of stress, especially from watching upsetting events on television, said lead researcher Alison Holman of the University of California-Irvine. About two-thirds of the participants watched the Sept. 11 attacks on live television.

The study reported the increased rates even after taking into account other factors that could cause similar ailments, such as smoking and diabetes.