The study?s results suggest that cosmic radiation damages a particular chromosome in exactly the same way as radiation therapy does. Maryanne Gundestrup, MD, of the University Hospital in Copenhagen, Denmark and colleagues, studied the chromosomes of seven aircrew members with acute myeloid leukemia or myelodysplasia (a condition that often develops into acute myeloid leukemia) and found that in four of the aircrew, the same section of one of their chromosomes was deleted. The researchers found a similar abnormality in eight of 19 patients who acquired leukemia after receiving radiation therapy.

The results indicate that the genetic deletion could be an indicator of previous exposure to ionizing radiation, according to the researchers, who say larger studies will be needed to confirm a link between myelodysplasia, acute myeloid leukemia, and exposure to cosmic radiation in aircrew.

The study is a follow-up to a study published a year ago by the same researchers in The Lancet (Vol. 354, No. 9195). The earlier study, involving nearly 4,000 cockpit crew members, showed that prolonged exposure of more than 5,000 hours to cosmic radiation increased the risk of acute myeloid leukemia about five-fold.

Risk to passengers is low

Cosmic radiation does not appear to threaten the average airline passenger, however. "The general population is not exposed to the same amount of flight hours as a commercial aircrew," Gundestrup says. "Smoking and car driving is many times more dangerous," she says.

According to a Federal Aviation Administration (FAA) advisory on radiation exposure, air travelers are exposed to about a 100-fold more biologically harmful dose at 35,000 feet than on the ground. Ionizing radiation, however, found in both cosmic radiation and radiation therapy, can damage DNA and increase the risk of cancer.

"It is important to remember that flying is safe and that our findings have to be confirmed in larger studies," Gundestrup. She recommends that cockpit crew who are concerned about reducing their risk try to reduce ''passive flying'' on their way to duty as well as the amount of active flying if possible. "The only way to prevent exposure to cosmic radiation is to fly fewer hours," she says.

"This paper is interesting and provocative--perhaps it will lead to further studies," says H. Stacy Vereen, MD. Vereen, who is an FAA-designated Senior Aviation Medical Examiner and president of the Civil Aviation Medical Association, says, "Even though the risk to pilots is relatively small, we are all interested in reducing that risk to zero. Just as safety features are developed to reduce the risk of injury in automobile accidents, hopefully we will develop engineering methods to reduce the exposure and hence the risk of high-altitude cosmic radiation."