We have conducted a large and comprehensive study characterizing cancer rates among U.S. cabin crew relative to the general U.S. population, which adds to the relatively sparse literature regarding cabin crew health and has included profiling a wide range of cancers. Consistent with previous studies reporting on cancer incidence and mortality among flight attendants, we report a higher prevalence of breast, melanoma and non-melanoma skin cancers (comprising basal cell and squamous cell carcinomas) among this occupational group relative to the general population. This is striking given the low rates of overweight and smoking among flight attendants in our study population, which we take to be indicators of general health and healthy behaviors, as well as being independent risk factors for some cancers [1, 11]. We also report associations between job tenure as a flight attendant and several cancer outcomes, consistent with previous U.S. and European studies [7–11], though we note that our reliance on cancer prevalence rather than incidence complicates the interpretation of our findings with regard to the timing of both work exposures and cancer outcomes, and the conflation of cancer incidence and survivorship. Nevertheless, our study extends the sparse literature on this important topic, confirms previous findings, and is the first study to note an increase in non-melanoma skin cancer among U.S. cabin crew (consistent with studies of European cabin crew and pilots). Our work informs future research directions regarding the health of this understudied group of workers and highlights the question of what can be done to minimize the adverse exposures and cancers common among cabin crew. 
 
 Our finding of a greater prevalence of breast and skin cancers among flight attendants is consistent with most of the epidemiologic literature on this topic to date [7–11]. As noted above, our study is the first to show an increase in non-melanoma skin cancer among U.S. cabin crew relative to the general population, which replicates findings among European flight attendants and pilots [11, 24]. We also observed that job tenure as a flight attendant was associated with the prevalence of non-melanoma skin cancer, as well as breast cancer (within parity subgroups), among females. We were also able to conduct SPR analyses among crew with in-flight secondhand smoke exposure prior to 1988 and found that some associations were strengthened among this subset of participants. Interpretation of the latter results is somewhat hampered by the fact that participants’ occupational secondhand exposures ended by 1998 at the latest, and studies regarding smoking or secondhand smoking exposures and breast and skin cancers have reported mixed results [25, 26]. However, secondhand smoke has been linked to breast and skin cancers in some studies and is certainly a potential risk factor for these cancers, and unlike for cardiovascular disease, smoking-related risk of cancer never falls to baseline, even years after cessation of the exposure [25, 26]. 
 
 Our results are also consistent with cabin crews’ occupational exposures to ionizing radiation [2, 6], Circadian rhythm disruption [3], historical exposures to in-flight secondhand smoke [5], and ongoing exposures to other chemical agents [2], most of which are classified as confirmed or probable carcinogens in humans [27–29]. Ionizing radiation is a known causal factor for non-melanoma skin cancer and breast cancer [27], whereas the studies regarding melanoma in relation to ionizing radiation are more conflicted [30]. It should be noted that cabin crew have the largest annual ionizing radiation dose of all U.S. workers (e.g. 3.07 mSv vs. 0.59 mSv for U.S. Department of Energy workers) [5]. These exposures can easily exceed guidelines released by the NCRP or the International Commission on Radiological Protection [6, 31]. Although we evaluated job tenure prior to age 45 or age 40 in relation to cancer prevalence, in part to isolate the potential effects of ionizing radiation exposure at younger ages, these restrictions generally did not meaningfully alter our results. This may be because ionizing radiation exposure is also important to cancer risk at older ages, and because it is difficult to disentangle the relevant exposure years in our study population, which has a median tenure of 19 years of employment and for which cancer diagnosis date was not recorded. One possible exception is for breast cancer, for which associations were somewhat stronger when evaluating tenure prior age 45 rather than lifetime tenure. These results, while imprecise and requiring replication in a study that estimates cosmic ionizing radiation exposure directly (rather than using tenure as a proxy), may suggest that flight-related exposures are most important to breast cancer risk when occurring at earlier ages. 
 
 We report associations between duration of employment as a flight attendant and breast cancer risk among women who had three or more children, with some evidence of an association among nulliparous women as well, though the latter association was imprecise. Nulliparity is a risk factor for breast cancer, and women who are parous may be less susceptible to the effects of carcinogenic exposures on the breast due to breast cell differentiation occurring after a first pregnancy [32, 33]. Hence, our findings of a somewhat stronger association between job tenure and breast cancer among nulliparous women is consistent with the current state of biologic and epidemiologic knowledge, though it should be noted that the few relevant previous studies among cabin crew did not show increased risk of breast cancer among nulliparous relative to parous participants [20, 21, 34]. Our findings of a stronger association between tenure as a flight attendant and breast cancer among women with three or more children is, interestingly, consistent with two other recent publications on this topic among cabin crew [20, 21]. The authors of the latter studies, which evaluated breast cancer in relation to calculated cosmic radiation exposure and Circadian rhythm disruption, hypothesized that these unexpected results may be due to Circadian rhythm changes from shift work and crossing time zones [21], especially since flight attendants report a much higher rate of sleep disorders and disturbances relative to the general population [11, 12] and these effects may be exacerbated among women with young children who have greater sleep disruptions from both their home and work lives [21]. 
 
 Limitations of our study include its cross-sectional design, which precludes inferences about causality, as an observed association may reflect the effect of flight attendant work on a given condition, or the effect of an outcome on a factor related to employment as a flight attendant. Use of structured questionnaires, as in our study, aims to minimize this bias. We also note a further limitation that the date of cancer diagnosis was not recorded in the FAHS questionnaire. Hence, some reported cancers may have been diagnosed prior to employment as a flight attendant, and some flight attendant work (i.e. exposure) may have occurred following a cancer diagnosis, making the direction of the potential bias unclear. These limitations are counteracted in part by our analyses evaluating job tenure prior to age 40 and 45 years in relation to cancer prevalences, as many cancers, including of the skin and breast, occur later in life. Therefore, this restriction increases the probability that the exposure of interest occurred prior to the reported cancer outcome. 
 
 Another potential limitation of our study involves the question of whether a population of flight attendants is sufficiently comparable to the general U.S. population with regard to cancer risk factors, and whether differences in risk factors may introduce bias to the SPRs. For example, we report substantial differences in racial profile, smoking status, overweight prevalence, and number of live births between the FAHS and NHANES cohorts, all of which are related to the risk of various cancers. We have counteracted this issue in part by restricting the NHANES comparison group to currently employed adults with at least a high school degree and above a certain income to poverty ratio, and by conducting sensitivity analyses restricting to non-Hispanic white participants that showed no meaningful differences from our main results. We also note that the FAHS includes a substantially smaller percentage of current smokers and overweight participants than the NHANES population, which would be expected to decrease the risk of several cancers, whereas we consistently observed increased cancer SPRs. At the same time, we should note that FAHS participants had fewer children than NHANES participants (which elevates the risk of breast cancer), though this is in part ameliorated by the fact that we observed associations between tenure as a flight attendant and breast cancer within parity subgroups. Even with the above reported sensitivity analyses, we acknowledge that the potential for residual confounding by cancer risk factor profile differences between the two study populations (such as for race and parity) still exists. 
 
 In addition, health outcomes in our study and in the NHANES were based on self-report; validation through medical records was not possible due to the scope and cost of this endeavor. Validity of self-reported health outcomes varies by study population and the outcome of interest. Sensitivity and specificity of self-reported outcomes relative to medical records or linkage to disease registries were found to be moderate to high for common cancers (including breast cancer and melanoma), particularly among those with higher socioeconomic status, such as in our well-educated cohort [35]. However, this has not been the case for non-melanoma skin cancer. We should note that non-melanoma skin cancers are excluded from most U.S. cancer registries and may be under-reported by those that do include it [36]. This may explain why non-melanoma skin cancer assessed through the California Cancer Registry was not related to flight attendant work in a previous study [9], in contrast to many other studies conducted among cabin crew and pilots, including our own research presented here [11, 24]. 
 
 A further limitation of our study is that we recruited flight attendants from a mix of company rosters, on-site airport recruitment, and an online/social media presence. Recruiting volunteer participants not recruited from employee files may have contributed to selection bias. For example, volunteer participants may differ from those recruited using a more randomized approach in terms of various factors, including their socioeconomic status, attitude toward health research, and factors related to time and ability to complete online surveys (which may also be related to health), as discussed in a recent analysis with regard to online recruitment in the Heart eHealth Study relative to NHANES [37]. However, the above analysis reported that, while selection bias was likely on a variety of factors, such as gender and marital status, it was much less likely to affect internal (rather than external) validity of exposure-outcome associations [37]. This is likely to be especially true in a relatively homogenous workforce than in a general population study recruited online. It is also important to note that an online recruitment strategy has many advantages in terms of efficiency, reliability of data collection and coding, and the ability to reach a wider range of potential study participants [37]. 
 
 Our study may have attracted a disproportionate number of flight attendants with cancer, leading to detection bias, as flight attendants with worse health are likely to be more motivated to participate in an epidemiological study of flight attendant health, are likely to attend regular medical check-ups (this is true for flight attendants in general), and the question of cancer risk in relation to flight exposures is well known within the aviation community. However, it is reassuring that our results are consistent with previous studies that recruited participants from employee rosters [8–10]. 
 
 Additional limitations of our study include reliance on job tenure as a surrogate for occupational exposures, lack of correction for multiple testing, insufficient power to evaluate less common cancers, and insufficient information on confounders for some cancers. In particular, we were not able to control for leisure-time UV exposure when evaluating skin cancer risk, though it should be noted that a large study found no difference in sunbathing habits between flight attendants and the general population [38]. We plan to evaluate specific exposures in future individual exposure-outcome analyses. Finally, we note that our reliance on prevalence rather than incidence of cancer confuses the issues of cancer risk and survivorship in interpreting our results. This is in part ameliorated by the fact that breast and skin cancers have relatively low mortality rates (especially for basal cell carcinoma, which is not considered fatal or disabling), and that we are comparing to prevalence rates in NHANES as well. Nevertheless, the limitation remains, and it is also important to note that flight attendants may differ from the general population of U.S. workers with regard to health insurance access, paid leave policies, and other benefits that could affect survivorship, and may be more likely to have access to an urban center with better quality health care for cancer treatment. It is reassuring that our results are consistent with previous studies that relied on cancer incidence [9, 10]. 
 
 Strengths of our study include access to the resources of a large cohort of cabin crew with information on a range of cancer outcomes, work experiences, and potential confounders. In addition, online questionnaires are an increasingly popular option in epidemiologic research, including high profile studies such as the Millennium Cohort and the Nurses’ Health Study 3 [39]. This mode of data collection allows for validation checks, reduced data entry and coding errors, personalized question administration, convenience to participants, equal or better validity compared to hard copy questionnaires, and the collection of metadata, such as date, time, and time to completion, which can be used for quality control and sensitivity analyses [39]. 
 
 Our study findings contribute to the sparse literature on flight attendant health, which may also be applicable to passengers, especially frequent flyers. Conducting high quality studies within this group of workers is important given that U.S. cabin crew are subject to fewer protections than most workers in this country and relative to flight attendants working in the European Union (EU). For example, the EU requires airlines to monitor radiation dose, organize schedules to reduce radiation exposure, and inform workers of current studies [40]. ||||| TIME Health For more, visit TIME Health 
 
 Flight attendants are exposed to a number of known cancer-causing risks, but few studies have rigorously quantified that risk, and researchers say they are an understudied occupational group. 
 
 The Harvard Flight Attendant Health Study (FAHS), begun in 2007, addresses some of the gaps in understanding health risks among flight attendants. In the latest report, published in the journal Environmental Health, researchers found that flight attendants had higher rates of many cancers, including breast cancer and melanoma, compared to the general population. 
 
 The FAHS included more than 5,300 flight attendants who were recruited through online and mailed surveys, and given in person at airports. The flight attendants answered questions about their flight schedules, as well as any diagnoses of cancer. The researchers, led by Irina Mordukhovich, a research associate at Harvard T. H. Chan School of Public Health, then compared the responses to those from a matched group of people not in the airline profession from an ongoing national health survey. 
 
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 Mordukhovich found higher prevalence of breast, melanoma, uterine, gastrointestinal, thyroid and cervical cancers among the flight attendants compared to the general public. The study also revealed for the first time a higher rate of non-melanoma skin cancers, such as basal cell and squamous cell carcinomas, among flight attendants. 
 
 The prevalence of breast, melanoma and non-melanoma cancers were especially striking, says Mordukhovich. Flight attendants had a 51% higher prevalence of breast cancers, more than two-fold higher prevalence of melanoma and four-fold greater prevalence of non melanoma skin cancers, compared to people not in the profession. 
 
 “Flight attendants are considered a historically understudied occupational group, so there is a lot we don’t know about their health,” says Mordukhovich. “What we do know for sure is the exposures that both pilots and flight attendants have—the main one being high radiation levels because of cosmic radiation at altitude.” That exposure may not be concerning for people taking individual flights, but for people whose jobs involve flying, that risk may have a negative effect on their health, as the study results suggest. 
 
 “Little attention has been paid to job-related cancer risks for flight attendants,” says Sara Nelson, international president of the Association of Flight Attendants-CWA, a labor union group that represents 50,000 flight attendants, in a written response to TIME about the study. “The Harvard study shines light on this issue. Job-related cancer risk factors identified in the study include exposure to ionizing radiation, jet lag, pesticides, and other onboard chemicals. We will use the results to encourage airlines, airline manufacturers, and regulators to prevent exposures and change working conditions to reduce risk.” 
 
 While cosmic radiation originates in outer space, small amounts reach the earth, and greater chances of exposure occur at higher altitudes. The World Health Organization’s International Agency for Research on Cancer determined that ionizing radiation, like that found in cosmic radiation, can contribute to cancer in people. 
 
 The National Council on Radiation Protection and Measurements reports that flight crews are exposed to the largest annual dose of radiation among U.S. radiation workers. But there are no limitations or regulations in the U.S. on how much exposure is safe for flight attendants. (Other radiation workers have certain occupational safety regulations in place to protect them from exposure and restrict risky exposure.) The European Union regulates flight attendant schedules and flying time of pregnant flight attendants to limit potentially dangerous exposures. 
 
 Flight attendants also have disrupted sleep schedules, since they frequently cross time zones and aren’t able to maintain a regular circadian wake-sleep cycle. Other studies have linked shift work and disrupted circadian clocks to higher risk of breast and prostate cancers, possibly due to a reduced ability of DNA to repair itself and the way circadian rhythm processes may be connected to immune function. 
 
 
 
 
 
 Mordukhovich says that the results need to be repeated by other groups to confirm the risk, but the data should raise concerns about the risk of cancer for flight attendants. (The risk for pilots may be similar, but this study focused specifically on flight attendants.) The Association of Flight Attendants did not provide comment in time for publication. 
 
 The findings are particularly worrisome considering that according to data the study collected, flight attendants are in many respects healthier than the general public. They are, for example, less likely to smoke or be overweight, and have lower rates of heart disease. 
 
 “The fact that we are seeing higher cancer rates in this study population is definitely striking,” she says. “We hope the study highlights issues about exposures that we know are problematic for flight attendants and pilots and aren’t currently being addressed. We have known carcinogens that flight crews are exposed to, and we’re hoping that this study allows people to start thinking about what should be done to implement protections.” ||||| Flight attendants may have a higher risk of a number of cancers, a new study finds. 
 
 Researchers found that women and men on U.S. cabin crews have higher rates of many types of cancer, compared with the general population. This includes cancers of the breast, cervix, skin, thyroid and uterus, as well as gastrointestinal system cancers, which include colon, stomach, esophageal, liver and pancreatic cancers. 
 
 One possible explanation for these increased rates is that flight attendants are exposed to a lot of known and potential carcinogens, or cancer-causing agents, within their work environment, said lead study author Irina Mordukhovich, a research associate at Harvard University's T.H. Chan School of Public Health. [10 Do's and Don'ts to Reduce Your Risk of Cancer] 
 
 One of those carcinogens is cosmic ionizing radiation, which is elevated at higher altitudes, Mordukhovich told Live Science. This type of radiation is particularly damaging to DNA and is a known cause of breast cancer and nonmelanoma skin cancer, she said. 
 
 Air cabin crews receive the highest yearly dose of ionizing radiation on the job of all U.S. workers, she added. 
 
 In the new study, the researchers looked at data from more than 5,300 flight attendants from different airlines who completed an online survey as part of the Harvard Flight Attendant Health Study. The analysis looked at the cancer rates in these flight attendants compared to a group of about 2,700 people who had a similar income and educational status but were not flight attendants. 
 
 The researchers found that in female flight attendants, the rates of breast cancer were about 50 percent higher than in women from the general population. In addition, melanoma rates were more than two times higher and nonmelanoma skin cancer rates were about four times higher in female flight attendants compared with women from the general population. (Nonmelanoma skin cancers include basal cell and squamous cell carcinomas.) 
 
 These elevated cancer rates were observed despite indications of good-health behaviors, such as low levels of smoking and obesity, in the flight-attendant group as a whole, the study authors said. 
 
 Cancer rates in male flight attendants were nearly 50 percent higher for melanoma and about 10 percent higher for nonmelanoma skin cancers compared with men from the general population group, according to the findings. 
 
 The potential cancer risks for flight attendants are not limited to cosmic ionizing radiation. Cabin crew members are also regularly exposed to more UV radiation than the general population, which can make these workers more vulnerable to skin cancers, Mordukhovich said. 
 
 In addition, some studies have found that circadian rhythm disruptions, such as jet lag, might be linked with an increased risk of cancer, she said. These disruptions could lead to changes in immune function and cell metabolism, which can reduce the suppression of tumors. 
 
 Another possible threat to the health of cabin crew members is chemical exposure, according to the study. The women and men who worked as flight attendants prior to 1988, when smoking was first banned on some U.S. flights, were routinely exposed to secondhand smoke while on board the aircraft. 
 
 Other chemical contaminants found in the cabin may include engine leakages, pesticides and flame retardants, which contain compounds that may act as hormone disruptors and increase the risk of some cancers, Mordukhovich said. 
 
 Further complicating matters is that flight attendants in the U.S. don't have the same occupational protections as their counterparts in the European Union. There, exposure levels to radiation as well as work schedules are routinely monitored and adjusted to make sure flight attendants don't exceed certain guidelines for carcinogen exposure, Mordukhovich said. [5 Real Hazards of Air Travel] 
 
 There has been only limited research on the health of flight attendants, but they may not be the only air travelers to experience higher rates of cancer. The rates may also be higher for pilots and people who fly often as passengers, Mordukhovich said. Studies of pilots have generally shown higher rates of skin and prostate cancers, she noted, adding that pilots also have been found to have circadian rhythm disruption, but these workers have somewhat more built-in protections around their scheduling and rest times than flight attendants do. 
 
 Although the cancer risks for frequent flyers have not yet been studied, there is no reason to suspect these people would not have similar risks as those faced by cabin crews, Mordukhovich said. 
 
 Some limitations of the study are that researchers were not able to take into consideration individual UV exposures, such as sunbathing habits or leisure-time activities, which could influence skin cancer risk. In addition, cancer rates were self-reported by study participants, and these diagnoses were not confirmed by a check of their medical records by the researchers, according to the study. 
 
 The study was published online today (June 25) in the journal Environmental Health. 
 
 Originally published on Live Science.
– Unfortunate news for flight attendants: A new study finds that they suffer from higher rates of many types of cancer than the general population. The researchers compared data from more than 5,300 flight attendants who completed a health survey to about 2,700 non-flight-attendants with similar income and educational status, LiveScience reports. Among their most striking findings: Female flight attendants had rates of breast cancer about 50% higher than women who weren't flight attendants; they also had melanoma rates more than two times higher and non-melanoma skin cancer rates about four times higher. And male flight attendants had melanoma rates of almost 50% higher than the general population of males and non-melanoma skin cancer rates of about 10% higher. Air cabin crew members were also found to have higher rates of cancers of the cervix, thyroid, and uterus, as well as gastrointestinal system cancers including colon, stomach, esophageal, liver, and pancreatic cancers. This despite the fact that the flight attendant group had, as a whole, indications of healthy behaviors including low levels of smoking and obesity. The researchers point out several possible reasons for the increased cancer risk: Flight attendants are exposed to many known and potential carcinogens, including the US' highest on-the-job dose of cosmic ionizing radiation, which is known to cause breast cancer and skin cancer. As Time explains, cosmic radiation originates in space, but small amounts make it to earth and exposure is more likely at higher altitudes. Cabin crew members are also regularly exposed to UV radiation and chemical contaminants from engine leakages, flame retardants, and more. Their circadian rhythms can be disrupted by jet lag, and such disruptions have also been linked to an increased risk of cancer. Researchers say pilots and frequent flyers may be at similar risk for the same reasons. (Here are five things airline workers would tell you if they could.)