A long-term study of U.S. Navy veterans found little increased disease risk associated with exposure to radar. The report, which involved over 40 years of follow-up, was published in the May issue of the American Journal of Epidemiology.

There has long been public concern that exposure to low energy, non-ionizing electromagnetic radiation, including that associated with power lines, electrical appliances, cellular telephones and radar, may have significant health effects. Unlike higher energy, ionizing radiation (such as X-rays), which has been linked to increased cancer risks, lower energy radiation has shown no consistent association.

An earlier study published in 1980 by the Medical Follow-up Agency of the National Academy of Sciences suggested a possible link between high radar exposure and lung cancer. The current report extends the earlier report an additional 25 years.

The study involved 40,581 male veterans who graduated from Navy technical schools between 1950 and 1954 and served on ships or in air squadrons during the Korean War. Approximately half (20,021) had jobs with the potential for high levels of microwave exposure from radar ("high exposure" group); the other half (20,560) held jobs thought to involve low levels of radar exposure ("low exposure" group).

The researchers compared the mortality rates of the veterans to the rates for the general U.S. male population. The death rates for the high and low exposure groups were then compared to each other.

Compared to the general population, there was no increased risk of any disease either for the entire group of veterans, or for either of the two exposure groups. Overall, 8,393 deaths occurred among the veterans, while over 11,300 deaths would be expected, based on death rates in the general population.

For several diseases, such as lung cancer, diabetes, and vascular, digestive and nonmalignant respiratory diseases, the veteran death rates were significantly lower than for the general population; for other cancers, the rates of the veterans were less than (e.g. brain cancer, testicular cancer and lymphoma) or similar to (e.g. leukemia) those in the general population. However, the Navy veterans were significantly more likely to have died from air transportation accidents or injuries resulting from war operations.

The death rates for all diseases were significantly less for both the low exposure (20 percent less) and the high exposure (35 percent less) groups than the rate for the general U.S. male population. The lower disease rates observed in these veterans support previous studies showing that servicemen tend to be healthier than the general population; this is known as the healthy soldier effect. This study showed little diminution of the healthy soldier effect even 40 years after entering military service.

When the scientists compared the death rates among the high and low exposure veterans to each other, they found that for most diseases and most types of cancer, the veterans with higher potential microwave exposure had lower disease rates than the low-exposure veterans.

For example, mortality rates for chronic obstructive lung disease, ischemic heart disease (a condition involving obstruction of blood vessels), diabetes, and lung and brain cancers were less for the higher than for the lower exposure groups. The lower death rate for smoking-related diseases in the high radar exposure group was contrary to the lung cancer finding in the earlier report based on this cohort, and may reflect lower smoking rates.

The exception to the trend of lower mortality rates in the high exposure occupations was non-lymphocytic leukemia, particularly acute myeloid leukemia (a cancer of white blood cells known as myeloid cells). Increased leukemia mortality was observed primarily in aviation electronics technicians, a group which was observed to have over twice the risk of non-lymphocytic leukemia as that in the general population (i.e., 12 non-lymphocytic leukemia deaths compared to 5.5 such deaths expected based on general population rates).

Aviation electronics technicians were one of three groups of veterans assigned to the "high exposure" group which also included electronics technicians and fire control technicians. Electronic technicians and fire control technicians had non-lymphocytic leukemia rates comparable to those in the general population.

The researchers note that the increased leukemia risk for aviation electronics technicians should be interpreted cautiously. The estimated elevated risk of leukemia may be related to occupational exposures other than radar or to lifestyle factors unrelated to occupation, or it may simply have been due to chance. If radar exposure causes leukemia, then increased risks would have been expected in the other two high exposure occupations as well. Thus, the authors conclude that it is unlikely that radar exposure is causally associated with increased leukemia risk.

Previous studies on the health effects of radar and other types of low energy electromagnetic radiation have shown no clear association with cancer. In a study of men who served in the U.S. Navy from 1974 through 1984 by the Naval Health Research Center no increased leukemia risks were seen among aviation electronics technicians or other occupation with high radar exposures.

On the other hand, a small increased risk of leukemia was reported among electrician's mates, who had little occupational exposure to radar.

The electromagnetic spectrum covers an enormous range of wavelengths (see chart to the left). As the wavelength gets shorter, the energy increases. At the shortest wavelengths, ionizing radiation such as X-rays or gamma rays is known to break molecular bonds and cause cancer, but the health effects of longer wavelength radiation are uncertain. The energy associated with power lines, electrical appliances, and radar is much too low to break molecular bonds.

In general, no consistent epidemiologic or laboratory associations of low energy radiation with cancer have been shown. Several reports looking at the health effects of electromagnetic fields associated with power lines and household appliances are largely negative. Studies looking at the effect of cellular telephones on brain tumors and leukemia have found no increased risk. The associations between radar exposure and cancer from other epidemiologic studies are weak and inconclusive. According to the current report, radar exposure appears to have very little, if any, effect on mortality.

SOURCES:
American Journal of Epidemiology, May 2002; 155(9):810-818
National Cancer Institute (http://www.nci.nih.gov)