With Pesach quickly approaching, and summer break just around the corner, it won’t be long before many of us are booking airline tickets. On any given day more than 87,000 flights take off in the United States alone, yet despite its convenience and popularity, air travel is not without risk. Plane crashes, disappearance of aircrafts and terror attacks are obvious risks associated with air travel, however, statistically speaking these risks do not pose much concern. The true risks associated with air travel are those which pose genotoxic (a term referring to agents that are damaging to the cell’s genetic information) affects — those being the threats posed by airport security screenings, cosmic radiation, UV rays and circadian disruption (jet lag).
Despite popular opinion, the radiation from airport security scanners is emitted in very small quantities. One scan delivers only about 0.005 to 0.01 millirem, quantities way below the 10,000 millirem danger threshold. Interestingly, dental x-rays, mammograms, and CT scans all expose individuals to over 1,000 times more millirem than the security scanners, and it is therefore safe to assume that the screenings do not pose threats to travelers.
The radiation that may pose a greater threat to travelers and aircrews, however, is cosmic ionizing radiation. One minute of flying at an altitude of 35,000 feet may potentially expose someone to as much radiation as a single security scan. Cosmic radiation or cosmic rays are high energy charged particles of extraterrestrial origin that bombard the earth constantly from all directions. Cosmic radiation exposure at high altitudes is much greater than at sea level, as the Earth’s atmospheric layer provides a shielding effect which is equivalent to 13 feet of concrete. It is estimated that a typical pilot would incur an annual median cosmic radiation dose of 1.92 mSv- doses higher than the International Commission on Radiological Protection’s recommended effective dose limit of 1 mSv.
The effects of ionizing radiation (IR) have been studied in regard to telomeres and telomerase; telomeres are essential parts of our chromosomes that affect how our cells age, and telomerase is a specialized type of reverse transcriptase that maintains the length of the telomeres. Both the loss of function of telomerase and telomere length have been associated with genomic instability, and therefore are correlated to cancer. Studies have demonstrated that telomerase activity is altered after IR exposure, thereby suggesting that IR exposure has carcinogenic potential. With this in mind, many studies have been done to assess the instances of cancer amongst pilots and flight crew. It was seen that those with the heaviest exposure to cosmic radiation at a younger age had significant increased risk for overall cancer. Yet with the exception of both malignant melanoma and non-melanoma skin cancer, the fight crews exhibited an overall cancer incidence similar to that of the general population. Therefore despite the increased exposure to radiation, studies indicate that there is little evidence to directly link it to cancer development.
While the overall cancer risk did not correlate to cosmic radiation exposure, there does seem to be higher instances of skin cancers amongst pilots and flight crew, possibly due to UV exposure. Airplane windshields are often made out of polycarbonate plastic or multilayer composite glass, with UV-A transmission of .41- 53.5%. These windshields successfully block UV-B rays, but allow for UV-A transmission. It can therefore be calculated that Pilots flying for 56.6 minutes at 30,000 feet in the air receive the same amount of UV-A carcinogenic effective radiation as one would receive from a 20-minute tanning bed session. It is therefore possible to assume that the UV-A transmission inside airplanes play a role in pilots’ increased risk of melanoma, as the relationship between UV-A radiation and melanoma is well established.
Another possible genotoxic risk to flight personnel and passengers is that of circadian disruption or jet lag. Previous studies were unable to strongly link the cancer instances amongst flight personnel to cosmic radiation and thought has therefore turned toward the possibly of circadian disruption being a possible carcinogen. Circadian rhythm disruption has been linked to cancer genesis and development. Cancer research of mice has observed faster tumor growth and more instances of metastasis in mice exposed to jet lag conditions, as compared to mice observed under normal conditions. Such research indicates that chronic circadian disruption can promote tumor growth, metastases and tumor progression; possible risks for flight personnel constantly flying over different time zones.
Multiple studies indicate that there is a very real risk of various forms of radiation exposure to those operating and flying in a plane. The above research indicates that landing safely does not necessarily mean that one was truly safe during a flight. The potential genotoxic risks associated with flying are something that certainly must be considered.