NEW YORK (Reuters Health) - Among firefighters who die on the job, coronary heart disease is the leading cause of death, new research indicates. Active involvement in putting out a fire raises the risk of cardiac-related death more than 100-fold compared with nonemergency duties.

"We've provided the strongest evidence to date that specific firefighting duties can precipitate coronary heart disease events," Dr. Stephanos N. Kales told Reuters Health.

Kales, from the Harvard School of Public Health in Boston, and his team obtained data from the U.S. Fire Administration on deaths that occurred while firefighters were on duty or within 24 hours after an emergency response or training. The data encompassed the period from January 1994 to December 2004, excluding the 48-hour period following the September 11, 2001 terrorist attacks.

Out of 1144 firefighter deaths, 449 (39 percent) were due to heart disease; 32 percent occurred during fire suppression, 31 percent during alarm response or return, 12.5 percent during physical training, 9.4 percent during emergencies that didn't involve fires, and 15.4 percent during nonemergencies.

The national data show that roughly 1 percent of duty time is spent in putting out fires, the researchers reported in The New England Journal of Medicine.

Compared with nonemergency duties, the risk of death from heart disease during fire fighting is 136-times greater. The mortality risk is 14.1-times greater during alarm response, 10.5-times greater during return after an alarm, and 6.6-times greater during physical training.

Kales noted that, even though physical training is part of the job, "there is wide variability in fitness among fire-fighters, from tremendous athletes" to those who are overweight and out of shape.

"There is no consistent program of physical fitness in 70 percent of fire departments," he added. "Many fire stations have weights or exercise equipment, but it's one thing to have the equipment and another to make physical training a required part of the job."

The elevated risk during alarm response and return is likely due to the release of catecholamine, a chemical secreted during a "fight-or-flight" response, Kales continued.

The more fit one is after a burst of exertion, the faster the heart rate recovers. Therefore, a delayed or altered heart rate recovery during the alarm return period is a sign of underlying cardiovascular problems.

Of course, there may be other reasons for underlying heart disease, the investigator added, including physical and psychological stressors and toxic exposures.

In a related editorial, two physicians from the University of California in Los Angeles School of Public Health recommend that "modifiable risk factors, whether or not they are related to occupation, should be aggressively addressed."

Dr. Linda Rosenstock and Dr. Jorn Olsen also urge fire departments to mandate "preplacement and annual medical examinations for all firefighters," as well as the implementation of wellness and fitness programs to reduce risk factors.