When do EMFs disturb the heart?

Among the more perplexing observations to emerge from recent studies on the biological effects of electromagnetic fields (EMFs) is their ability to sometimes—but not always—blunt heart-rate variability (SN: 1/10/98, p. 29: http://www.sciencenews.org/sn_arc98/1_10_98/bob1.htm). A reanalysis of seven studies on people exposed to EMFs now suggests that a person must be aroused or stressed for EMFs to dampen heart-rate variability.

In an attempt to maintain such vital features as blood pressure and body temperature, the nervous system orders the heart fleetingly to pick up or slow down its pace. A few studies have shown that when exposed to EMFs, the body sometimes ignores those cues, resulting in an inflexible heart rate. Such low variability has been linked to an increased risk of heart attacks and was posited last year as one explanation for elevated rates of cardiovascular disease in electrical workers (SN: 1/30/99, p. 70).

The studies that showed EMFs dampening heart responses all disturbed the participants—usually by waking them during the night to collect blood, note Charles Graham of the Midwest Research Institute in Kansas City, Mo., and his colleagues. This suggests that EMFs’ effects on heart rate “occur most readily when accompanied by some form of concomitant increase in physiologic arousal,” Graham’s team says in the August Environmental Health Perspectives. If true, the researchers note, people experiencing chronic stress or significant sleep problems may face the greatest EMF-induced cardiovascular risks.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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