THURSDAY, Oct. 23, 2003 (HealthDayNews) -- A new set of studies adds to evidence that flight crews face an increased occupational risk of developing cancer.
Three studies, using data from air crews in two Nordic countries and involving several thousand cabin crew members, all point to an increased risk associated with working for long periods above the clouds.
In one study, researchers from Iceland studied cabin crews for malignant melanoma, one of the most deadly and aggressive skin cancers. They surveyed more than 1,000 pilots and cabin attendants and 2,000 others randomly selected from the general population, asking about physical and lifestyle risk factors. They found men who flew for a living doubled their chances of developing the condition, and women were at 3.5 times the increased risk.
"While there have been other studies that have shown higher incidences of skin cancer in air crews, this is one of the first to try to adjust for sunbathing and other lifestyle factors," says study author Dr. Vilhjalmur Rafnsson, a professor of preventive medicine at the University of Iceland. "And it shows that occupational risks are indeed a significant factor."
"All our routes here are in higher exposure zones, which are about double that of the equator, and that is important," Rafnsson explains. "Many people say that the amount of radiation is not a lot, but cosmic radiation has significantly greater amounts of neutron activity. There is a lot of uncertainty about the effects of these neutrons, which are morebiologically active than other types of ionizing neutrons."
Another Icelandic study of more than 1,500 female flight attendants, 35 of whom went on to develop breast cancer, also suggests that the occupation may be an significant factor in that disease as well.
Researchers in that study, which looked at more than 40 years of flying crew data, found women crew members who had worked in those positions for five or more years before 1971 were five times as likely to develop breast cancer as those who had been in service for less time before this date. The association remained after adjusting for reproductive factors.
And a Swedish study found that while the overall incidence of cancer was only slightly higher than the general population, incidences of malignant melanoma among both male and female cabin crew was two to three times higher. Moreover, it also discovered additional increases in incidences of other skin cancers among the male flight crew.
However, while that study found female flight attendants had a 30 percent increased risk of breast cancer, this was not statistically significant when adjusted, and researchers could not find any link between length of employment or cumulative hours worked. This led them to question whether other factors, such as reproductive patterns, might be contributory factors.
"While we don't have the confidence that this higher rate is relateddirectly to occupational factors," says study author Dr. Anette Linnersjö, of the Stockholm Center of Public Health, "it probably is a real increase because other studies showed similar results."
"It could also be explained by time lag or disruption of the body's rhythm," she adds. "We haven't enough data on exposure."
Researchers found that jet planes, which gained prevalence after 1971,fly higher in the atmosphere and for longer periods of time, routinelyexposing crews to cosmic radiation for long periods -- often 14 hours ormore at a time.
In an accompanying editorial, Dr. Elizabeth Whelan of the U.S. Centers for Disease Control and Prevention, wrote the average amount of exposure to ionizing radiation has increased over time due to this trend. She went on to suggest that irregular working hours and disturbances to the body's internal clock could also play a role in predisposing some to ill health.
"But the question still remains whether the increased risk found in these studies is due to work or lifestyle factors," she wrote. "The research does not yet provide definitive answers."
Nevertheless, Whelan concluded: "The evidence that flight crew are at increased risk for certain types of cancer is growing, and current concerns about potential hazards in this occupation are not without basis."
The findings appear in the November issue of Occupational and Environmental Medicine.