Risky flames: firefighter coronaries spike during blazes.

Fighting fires is hard on the heart. In fact, heart disease causes 45 percent of on-the-job deaths among firefighters, compared with only 22 percent among police officers. New research shows that a disproportionate number of the firefighter deaths--whether caused by heart attacks, arrhythmias, or blood clots--occur during blazes.

"This is the strongest evidence yet that specific duties, namely fire suppression, lead to deaths from heart disease," says researcher Stefanos N. Kales of the Cambridge Health Alliance and the Harvard School of Public Health. "It's an interaction between the fight-or-flight response and underlying heart disease."

When alarm bells ring, "the stress, the fear, the danger all kick in and [firefighters'] heart rates jump," Kales adds. In firefighters with blocked arteries or other risk factors, this strain can be too much.

Four years ago, a small study by Kales' group suggested that fighting fires leads to heart-related deaths. To buttress that work, the team reviewed reports of all on-duty firefighter deaths in the United States between 1994 and 2004, excluding those related to the Sept. 11, 2001, terrorist attacks.

Of the 1,144 deaths reported to the federal government's U.S. Fire Administration, Kales' team identified 449 as heart related.

The team classified each heart fatality by the firefighter's activity at the time of death. The researchers found that 32 percent of the deaths occurred while individuals faced fires. Moreover, 31 percent occurred as personnel traveled to or from fires. Of the others, 15 percent took place at a station, 12 percent during training, and 9 percent on nonfire calls.

To calculate the relative risk of heart death during each activity, the team collected data on how firefighters spend their time at small, medium, and large fire companies. They found that firefighters spend just 1 to 5 percent of on-duty time fighting fires, with the smaller stations fighting fewer fires. "A lot of their time is downtime, waiting for something to happen," says Kales.

The odds of heart death while fighting a fire range from 12 to 136 times the odds of heart death during nonemergency duties, according to the size of the station, the team reports in the March 22 New England Journal of Medicine.

Linda Rosenstock, dean of the School of Public Health at the University of California, Los Angeles, calls the findings "not surprising? Heavy exertion while at high temperatures, combined with breathing smoke and chemicals, may trigger coronary events.

Physical fitness is also an issue. "Firefighters start out healthy" but don't necessarily stay in good shape during their years of service, Rosenstock says in a commentary accompanying the new report.

Fire fighters usually pass fitness exams upon hiring, but most departments have no ongoing fitness requirements, says Kales. Both he and Rosenstock call on fire departments to encourage better fitness for the nation's 1.1 million paid and volunteer firefighters.

Both the International Association of Fire Fighters and the International Association of Fire Chiefs have voluntary fitness initiatives. The programs should be mandatory, Kales says, so that firefighters "stay healthy throughout their careers."