Electromagnetic fields may damage hearts.

Men who worked in the presence of high electromagnetic fields (EMFs) were up to three times as likely to die from heart attacks and several other cardiovascular conditions as were their colleagues who had far smaller EMF exposures, a new study finds.

The observations emerge from a re-analysis of information collected during a 38-year study of almost 140,000 electric-utility workers.

EMFs are invisible lines of force that surround all electric devices and wiring. Their strength increases with the current running through the devices or wires.

Though high EMFs, especially their magnetic components, can promote the growth of cancers in laboratory animals (SN: 1/10/98, p. 29) and some evidence links them to cancers in people (SN: 6/30/90, p. 404), little attention had been paid to whether they might affect the heart.

Last year, however, Antonio Sastre and his coworkers at the Midwest Research Institute in Kansas City, Mo., published experimental data showing that 8-hour exposures to intermittent, 60-hertz fields altered heartbeat variability in healthy men.

Everyone's heart rate changes slightly from beat to beat, reflecting fine tuning by the nervous system in response to respiration and other factors, explains Sastre, a cardiovascular physiologist. Yet the magnitude of variance can differ dramatically between individuals, he notes. Even when two people each have a heart rate averaging 60 beats per minute (bpm), the heart rate of one might vary from 59 to 61 bpm, while another's swings broadly from 50 to 70 bpm.

Several studies have shown that low heart-rate variability correlates with a higher-than-normal risk of heart attacks and certain other heart conditions, particularly when the slowing occurs in the component of heart rate known as the low spectral band. In the February 1998 Bioelectromagnetics, Sastre's team reported a slowing in the low spectral band among men exposed to magnetic fields that cycle on and off every 15 seconds for an hour at a time.

When David A. Savitz, an epidemiologist at the University of North Carolina at Chapel Hill, learned of the findings, he invited Sastre to help him sift through data on heart-disease deaths within the large group of electrical workers.

The two researchers and their team now report that compared with men who worked in low-EMF jobs, men in trades exposed to high EMFs--such as linemen and power-plant operators--were far more likely to have died from heart attacks and heart conditions related to abnormal rhythms, or arrhythmias.

Moreover, risk of death from these conditions climbed as average EMF exposure increased. Savitz notes that men in the highest risk group tended to have worked in EMFs at least twice as high as those that people typically encounter in their homes.

Taken together, these data "suggest a possible association between occupational magnetic fields and arrhythmia-related heart disease," the researchers conclude in the Jan. 15 American Journal of Epidemiology. Savitz now plans to follow up with more-detailed studies, perhaps simultaneously monitoring heart-rate variability and EMFs among electricians at work.

Meanwhile, Jack Sahl, a Pasadena, Calif.-based consulting epidemiologist, is already leading a most recent study to test the Savitz team's most recent findings. Several years ago, while probing cancer rates among 50,000 southern California electrical workers, Sahl also detected an increased rate of heart disease among electricians, machinists, and others in "craft" trades with high EMF exposures. However, "I ignored the result," he now recalls, "because of my sense that heart disease was more likely to be related to lifestyle."

Indeed, Sahl remains "quite skeptical" of the putative EMF link, arguing that a heart-risky lifestyle--with heavy smoking, drinking, and consumption of a high-fat diet--"is more common among those craft workers with the high exposures to magnetic fields."