(HealthScoutNews) -- Air pollution may be damping the heartbeat enough -- even in young, healthy men -- to pave the way for heart disease later on, a new study suggests.

Air pollution changed the heart rates of healthy young men whose job sites were filled with dirty air, researchers say. But don't change occupations just yet. The researchers say more study is necessary to prove a connection between breathing polluted air and heart disease later in life.

"The reason for this study is that there have been community-based epidemiological studies that had linked pollution to cardiac death in the elderly. But nobody had looked at pollution and its effects on young, healthy people," says Dr. David Christiani, professor of occupational medicine and epidemiology at Harvard University's School of Public Health in Boston, Mass.

Christiani and his colleagues outfitted each of 40 male boilermakers and their apprentices with an air pollution-measuring device that scans for particles 2.5 micrograms or less in diameter. That's the size of ash and fossil fuel particulates that previous studies indicated was linked to increased heart disease, say the researchers.

The men, all about age 38, also wore monitors to record changes in heart rate.

Christiani says, "These were a good group of men to study because they were young and strapping, and they are also exposed on a regular basis to a varied level of fossil fuel particulates in the air."

Christiani says, "The central finding looked at a fairly simple outcome called heart rate variability. The heart rate varies quite a bit from minute to minute. You're sitting, standing, typing, breathing, emoting and your heart responds accordingly. And that's an important measure of health. So a decrease in that variability is a problem."

Variability also is a marker for heart disease in older people, he says.

And those "young, and strapping men" had a problem. Their normal heart rate variability, sampled every five minutes, decreased 2.6 percent for every milligram per cubic meter increase of the particulates, Christiani reports.

"So now what we have are two pieces of the puzzle -- lowered [heart rate] variability with established heart disease, and lowered variability in healthy people," Christiani says. "So the question is: Is exposure to particulates of this particular size and its subsequent decrease in heart variability related to heart disease?"

"That's something we need more research on," he says.

The findings appear in the latest issue of Circulation: Journal of the American Heart Association.

The American Heart Association says air pollution's poisonous chemicals can increase blood clotting, damage arteries and promote atherosclerosis, the buildup of fatty deposits in blood vessels. Pollutants also can damage the lungs, reducing the blood's ability to carry oxygen.

"What's being studied here is the non-voluntary part of the nervous system that controls heartbeat and all sorts of other bodily functions, like breathing," says Dr. Russell Luepker, head of epidemiology at the University of Minnesota in Minneapolis. "We do know that heart rate variability is a window into these non-voluntary parts of the nervous system known as autonomic function."

"Still, it's a long way from saying these men are getting heart disease from working in this environment. It's a hint -- a big hint -- but it's no firm evidence. It's still a long way from a causal relationship."

Christiani says, "We're continuing to research this. We've received funding from the National Institutes of Health, and we're going to follow up on this," he says.

What To Do: For more information on the possible link between air pollution and heart disease, see the American Heart Association or Boston's Beth Israel Deaconess Medical Center.

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