DALLAS (Reuters) - Exercise, long proven to prevent heart disease from developing in the first place, can also help people who have suffered heart attacks stay alive longer, doctors reported. Regular exercise reduces the risk of death or further heart disease at least as well as drugs do, if not better, several studies presented to a meeting of the American Heart Association in Dallas show. Dr. Michael Gaziano of Brigham and Women‘s Hospital in Boston studied more than 5,000 doctors who had suffered one heart attack. He asked them a number of questions, including how often they exercised to the point of "breaking a sweat". The doctors who broke a sweat two to four times a week reduced their risk of dying from another heart attack by 40 percent. Although the doctors were not asked about precisely what exercise they did or for how long, Gaziano said exercising hard enough and long enough to break a sweat is what counts. He said he was slightly surprised that people who already had heart disease did not endanger themselves by exercising. The doctors who exercised vigorously just once a week reduced their risk of all kinds of death by 20 to 30 percent. Those who exercised two to four times a week reduced the risk of dying from any cause by 40 percent over the period of the study, and their risk of dying from heart disease by 50 percent. Dr. Charles Hennekens of Harvard found a similar effect in 4,000 women with diabetes — which increases their risk of heart disease by three to six times. But exercise helped cancel out the danger. The exercising women reduced their risk of heart disease by 35 to 55 percent. Most of the women just walked — something Hennekens pointed out that almost everyone can do. A brisk walk is best, they said. Another study found one possible way that exercise reduces the risk of heart disease. Not only does it increase blood flow to and from the heart, but it can make the blood vessels work better, Dr. Rainier Hambrecht of the University of Leipzig found. He took patients with mild heart disease and forced them onto an intense exercise programme. After four weeks, catheters were threaded into the coronary vessels of 14 of the patients and the inside of their arteries, a lining known as the endothelium, was examined. "After exercise we found significant improvement … in the ability to dilate," Hambrecht told the news conference. The doctors are not hopeful that Americans will listen to their message any time soon.