Commentary: cancer in the air

Cancer incidence among male military and civil pilots and flight attendants: an analysis on published data

Flight personnel are exposed to cosmic ionizing radiation, chemicals (fuel, jet engine exhausts, cabin air pollutants), electromagnetic fields from cockpit instruments, and disrupted sleep patterns. Only recently has cancer risk among these workers been investigated. With the aim of increasing the precision of risk estimates of cancer incidence, follow-up studies reporting a standardized incidence ratio for cancer among male flight attendants, civil and military pilots were obtained from online databases and analysed. A meta-analysis was performed by applying a random effect model, obtaining a meta-standardized incidence ratio (SIR), and 95% confidence interval (CI). In male cabin attendants, and civil and military pilots, meta-SIRs were 3.42 (CI=1.94-6.06), 2.18 (1.69-2.80), 1.43 (1.09-1.87) for melanoma; and 7.46 (3.52-15.89), 1.88 (1.23-2.88), 1.80 (1.25-2.58) for other skin cancer, respectively. These tumors share as risk factors, ionizing radiation, recreational sun exposure and socioeconomic status. The meta-SIRs are not adjusted for confounding; the magnitude of risk for melanoma decreased when we corrected for socioeconomic status. In civil pilots, meta-SIR was 1.47 (1.06-2.05) for prostate cancer. Age (civil pilots are older than military pilots and cabin attendants) and disrupted sleep pattern (entailing hyposecretion of melatonin, which has been reported to suppress proliferative effects of androgen on prostate cancer cells) might be involved. In male cabin attendants, meta-SIR was 21.5 (2.25-205.8) for Kaposi’s sarcoma and 2.49 (1.03-6.03) for non-Hodgkin’s lymphoma. AIDS, which was the most frequent single cause of death in this occupational category, likely explains the excess of the latter two tumors.

Risk of breast cancer after night- and shift work: current evidence and ongoing studies in Denmark

Breast cancer is the most frequent cancer among women, and the number is increasing worldwide. This tumour is strongly associated with Western lifestyle, but the specific risk factors behind this observation are not well known. Exposure to light-at-night, including disturbance of the circadian rhythm, possibly mediated via the melatonin synthesis and clock genes, has been suggested as a contributing cause of breast cancer. Since shift- and night-time work is prevalent and increasing in modern societies, this exposure may be of public health concern, and contribute to the continuing elevation in breast cancer risk. Until now only few epidemiological studies have evaluated breast cancer risk after shift and night work. Although these studies are all suffering from methodological problems, especially concerning assessment of light exposure, results have consistently shown an increase in risk associated with night and shift work. Good opportunities for epidemiological cancer research exist in Denmark, and several studies on different aspects of breast cancer, work schedules, light exposure and melatonin levels are ongoing in order to further examine different aspects of this issue.

Cancer Incidence among Female Flight Attendants: A Meta-Analysis of Published Data

BACKGROUND

Flight attendants are exposed to cosmic ionizing radiation and other potential cancer risk factors, but only recently have epidemiological studies been performed to assess the risk of cancer among these workers. The aim of the present work was to evaluate the incidence of various types of cancer among female cabin attendants by combining cancer incidence estimates reported in published studies.

METHODS

All follow-up studies reporting standardized incidence ratio (SIR) for cancer among female flight attendants were obtained from online databases and analyzed. A metaanalysis was performed by applying Bayesian hierarchical models, which take into account studies that reported SIR = 0 and natural heterogeneity of study-specific SIRs.

RESULTS

A total of seven published studies reporting SIR for several cancer types were extracted. Meta-analysis showed a significant excess of melanoma (meta-SIR 2.15, 95% posterior interval [PI] 1.56-2.88) and breast carcinoma (meta-SIR 1.40; PI 1.19-1.65) and a slight but not significant excess of cancer incidence across types (meta-SIR 1.11, PI 0.98-1.25).

CONCLUSIONS

Although further studies are necessary to clarify the exact role of occupational exposure, all airlines should, as some companies do, estimate radiation dose, organize the schedules of crew members in order to reduce further exposure in highly exposed flight attendants, inform crew members about health risks, and give special protection to pregnant women.

Cosmic radiation exposure and cancer risk among flight crew

Nearly 20 epidemiologic or related studies of cancer incidence and mortality have been published during or since 2000, with several reporting increased risks of female breast cancer among flight attendants and melanoma among both pilots and cabin crew. Occasionally, excesses of other cancers have been observed, but not consistently. Although the real causes of these excess cancer risks are not known, there is concern that they may be related to occupational exposures to ionizing radiation of cosmic origin. It is possible that confounding risk factors may partially or totally explain the observed relationships, but several investigations are beginning to address lack of past adjustment for reproductive factors and sun exposure with improved study designs. With progress in aviation technology, planes will fly longer and at higher altitudes, and presumably the number of flights and passengers will increase. To respond responsibly to the real and perceived risks associated with flying, more extensive data are needed, but special efforts should be considered to ensure new projects can genuinely add to our current knowledge.

Integrating qualitative methods into occupational health research: a study of women flight attendants

AIMS

To identify possible work related sources of psychosocial stress in order to develop pertinent questionnaire items for a cross-sectional health survey of 3000 Italian women flight attendants, and to solicit suggestions on improving survey participation.

METHODS

Qualitative study in which 26 current and former women flight attendants participated: three focus groups of 6-7 participants each and six in-depth individual interviews. The session themes included positive and negative aspects of the job; relationships with colleagues, superiors, and passengers; perception of occupational risk for serious diseases; compatibility of work and family; and experiences of work related sources of stress and their effect on health. A transcript based analysis of the focus groups and interviews was used to identify emerging themes related to risk factors for mental health problems.

RESULTS

The participants indicated that mental health was a major concern. Several work related risk factors possibly related to adverse outcomes, such as depression and anxiety, were highlighted. These included isolation and solitude, fears of being inadequate partners and mothers due to job demands, passenger relationships, and lack of protection by employers with respect to workplace exposures and violent passengers. The information gained was used to develop a mental health module for inclusion in the health survey questionnaire which included questions on history of severe depression or anxiety, suicidal ideation or attempt, substance abuse, workplace sexual harassment, social support, leisure time activities, relationship with a partner, and role as mother.

CONCLUSIONS

Employing qualitative methods to identify work related sources of psychosocial stress enabled development of pertinent questionnaire items for a cross-sectional epidemiological study of women flight attendants. Follow up qualitative research may be necessary in order to put the cross-sectional study findings into context and to explore actions or strategies for preventing work related health problems evidenced from the survey.

Cancer incidence in airline cabin crew: experience from Sweden

AIMS

To determine the cancer incidence in Swedish cabin crew.

METHODS

Cancer incidence of cabin crew at the Swedish Scandinavian Airline System (SAS) (2324 women and 632 men) employed from 1957 to 1994 was determined during 1961-96 from the Swedish National Cancer Register. The cancer incidence in cabin crew was compared with that of the general Swedish population by comparing observed and expected number of cases through standardised incidence ratios (SIR). A nested case-control study was performed, including cancer cases diagnosed after 1979 and four controls per case matched by gender, age, and calendar year.

RESULTS

The SIR for cancer overall was 1.01 (95% CI 0.78 to 1.24) for women and 1.16 (95% CI 0.76 to 1.55) for men. Both men and women had an increased incidence of malignant melanoma of the skin (SIR 2.18 and 3.66 respectively) and men of non-melanoma skin cancer (SIR 4.42). Female cabin attendants had a non-significant increase of breast cancer (SIR 1.30; 95% CI 0.85 to 1.74). No clear associations were found between length of employment or cumulative block hours and cancer incidence.

CONCLUSIONS

Swedish cabin crew had an overall cancer incidence similar to that of the general population. An increased incidence of malignant melanoma and non-melanoma skin cancer may be associated with exposure to UV radiation, either at work or outside work. An increased risk of breast cancer in female cabin crew is consistent with our results and may in part be due to differences in reproductive history.

Light, timing of biological rhythms, and chronodisruption in man

This paper reviews abundant evidence suggesting that causes and course of aging and cancers can be considered as being both light- and rhythm-related. We define chronodisruption as a relevant disturbance of orderly biological rhythms over days and seasons and years in man. Light is the primary external mediator and melatonin a primary internal intermediary of such disturbances, which can result in earlier deaths via premature aging and cancers. We conclude that experimental and epidemiological research can provide further insights into common denominators of these chronic processes and may offer novel and uniform targets for prevention.