Lee C. Yong

Increased frequency of chromosome translocations in airline pilots with long-term flying experience

Background: Chromosome translocations are an established biomarker of cumulative exposure to external ionising radiation. Airline pilots are exposed to cosmic ionising radiation, but few flight crew studies have examined translocations in relation to flight experience. Methods: We determined the frequency of translocations in the peripheral blood lymphocytes of 83 airline pilots and 50 comparison subjects (mean age 47 and 46 years, respectively). Translocations were scored in an average of 1039 cell equivalents (CE) per subject using fluorescence in situ hybridisation (FISH) whole chromosome painting and expressed per 100 CE. Negative binomial regression models were used to assess the relationship between translocation frequency and exposure status and flight years, adjusting for age, diagnostic x ray procedures, and military flying. Results: There was no significant difference in the adjusted mean translocation frequency of pilots and comparison subjects (0.37 (SE 0.04) vs 0.38 (SE 0.06) translocations/100 CE, respectively). However, among pilots, the adjusted translocation frequency was significantly associated with flight years (p = 0.01) with rate ratios of 1.06 (95% CI 1.01 to 1.11) and 1.81 (95% CI 1.16 to 2.82) for a 1- and 10-year incremental increase in flight years, respectively. The adjusted rate ratio for pilots in the highest compared to the lowest quartile of flight years was 2.59 (95% CI 1.26 to 5.33). Conclusions: Our data suggests that pilots with long-term flying experience may be exposed to biologically significant doses of ionising radiation. Epidemiological studies with longer follow-up of larger cohorts of pilots with a wide range of radiation exposure levels are needed to clarify the relationship between cosmic radiation exposure and cancer risk.

Occupational Exposure to Polychlorinated Biphenyls and Risk of Breast Cancer

Background Despite the endocrine system activity exhibited by polychlorinated biphenyls (PCBs), recent studies have shown little association between PCB exposure and breast cancer mortality. Objectives To further evaluate the relation between PCB exposure and breast cancer risk, we studied incidence, a more sensitive end point than mortality, in an occupational cohort. Methods We followed 5,752 women employed for at least 1 year in one of three capacitor manufacturing facilities, identifying cases from questionnaires, cancer registries, and death certificates through 1998. We collected lifestyle and reproductive information via questionnaire from participants or next of kin and used semiquantitative job-exposure matrices for inhalation and dermal exposures combined. We generated standardized incidence ratios (SIRs) and standardized rate ratios and used Cox proportional hazards regression models to evaluate potential confounders and effect modifiers. Results Overall, the breast cancer SIR was 0.81 (95% confidence interval, 0.72–0.92; n = 257), and regression modeling showed little effect of employment duration or cumulative exposure. However, for the 362 women of questionnaire-identified races other than white, we observed positive, statistically significant associations with employment duration and cumulative exposure; only smoking, birth cohort, and self- or proxy questionnaire completion had statistically significant explanatory power when added to models with exposure metrics. Conclusions We found no overall elevation in breast cancer risk after occupational exposure to PCBs. However, the exposure-related risk elevations seen among nonwhite workers, although of limited interpretability given the small number of cases, warrant further investigation, because the usual reproductive risk factors accounted for little of the increased risk.

Quit interest, quit attempt and recent cigarette smoking cessation in the US working population, 2010

Objectives To determine the prevalence of cigarette smoking cessation and examine the association between cessation and various factors among workers in a nationally representative sample of US adults. Methods Data were derived from the 2010 National Health Interview Survey. Prevalence rates were calculated for interest in quitting smoking, making an attempt to quit smoking, and successful smoking cessation (defined as smokers who had quit for 6–12 months). Logistic regression analyses were used to identify factors associated with cessation after adjustment for demographic characteristics (age group, race/ethnicity, educational level and marital status). Results Data were available for 17 524 adults who were employed in the 12 months prior to interview. The prevalence of quit interest, quit attempt and recent cessation was 65.2%, 53.8% and 6.8%, respectively. Quit interest was less likely among workers with long work hours, but more likely among workers with job insecurity, or frequent workplace skin and/or respiratory exposures. Quit attempt was more likely among workers with a hostile work environment but less likely among workers living in a home that permitted smoking or who smoked ≥11 cigarettes/day. Recent smoking cessation was less likely among workers with frequent exposure to others smoking at work or living in a home that permitted smoking, but more likely among workers with health insurance. Conclusions Factors associated with cessation interest or attempt differed from those associated with successful cessation. Cessation success might be improved by reducing exposure to others smoking at work and home, and by improving access to health insurance.

High dietary antioxidant intakes are associated with decreased chromosome translocation frequency in airline pilots

BACKGROUND Dietary antioxidants may protect against DNA damage induced by endogenous and exogenous sources, including ionizing radiation (IR), but data from IR-exposed human populations are limited. OBJECTIVE The objective was to examine the association between the frequency of chromosome translocations, as a biomarker of cumulative DNA damage, and intakes of vitamins C and E and carotenoids in 82 male airline pilots. DESIGN Dietary intakes were estimated by using a self-administered semiquantitative food-frequency questionnaire. Translocations were scored by using fluorescence in situ hybridization with whole chromosome paints. Negative binomial regression was used to estimate rate ratios and 95% CIs, adjusted for potential confounders. RESULTS Significant and inverse associations were observed between translocation frequency and intakes of vitamin C, beta-carotene, beta-cryptoxanthin, and lutein-zeaxanthin from food (P < 0.05). Translocation frequency was not associated with the intake of vitamin E, alpha-carotene, or lycopene from food; total vitamin C or E from food and supplements; or vitamin C or E or multivitamin supplements. The adjusted rate ratios (95% CI) for > or =median compared with <median servings per week of high-vitamin C fruit and vegetables, citrus fruit, and green leafy vegetables were 0.61 (0.43, 0.86), 0.64 (0.46, 0.89), and 0.59 (0.43, 0.81), respectively. The strongest inverse association was observed for > or =median compared with <median combined intakes of vitamins C and E, beta-carotene, beta-cryptoxanthin, and lutein-zeaxanthin from food: 0.27 (0.14, 0.55). CONCLUSION High combined intakes of vitamins C and E, beta-carotene, beta-cryptoxanthin, and lutein-zeaxanthin from food, or a diet high in their food sources, may protect against cumulative DNA damage in IR-exposed persons.

Sleep-related problems in the US working population: prevalence and association with shiftwork status

Objective To estimate the prevalence of a comprehensive set of self-reported sleep problems by job characteristics, including shiftwork status, among a representative sample of US workers. Methods Data for 6338 workers aged ≥18 years were obtained from the National Health and Nutrition Examination Survey. Short sleep duration was defined as <7 hours per weekday/workday. Sleep quality was categorised as good, moderate and poor based on the frequency of 6 sleep-related symptoms. A sleep-related activities of daily living (ADL) score ≥2 was defined as impaired. Insomnia was defined as having poor sleep quality and impaired ADL. Shiftwork status was categorised as daytime, night, evening, rotating or another schedule. Prevalence rates were calculated and multivariate logistic regression analyses were used. Results The prevalence of short sleep duration (37.6% overall) was highest among night shift workers (61.8%; p<0.001). The prevalence of poor sleep quality was 19.2% among all workers, with the highest prevalence among night shift workers (30.7%, p=0.004). The prevalence of impaired ADL score (24.8% overall) and insomnia (8.8% overall) was also highest for night shift workers (36.2%, p=0.001 and 18.5%, p=0.013, respectively). In multivariate analysis, night shift workers had the highest likelihood of these sleep problems. Conclusions Self-reported short sleep duration, poor sleep quality, impaired ADL score and insomnia are common among US workers especially among night shift workers. Although these findings should be confirmed with objective sleep measures, they support the need for intervention programmes to improve sleep quantity and quality among night shift workers.

Mortality Among a Cohort of U.S. Commercial Airline Cockpit Crew

BACKGROUND We evaluated mortality among 5,964 former U.S. commercial cockpit crew (pilots and flight engineers). The outcomes of a priori interest were non-chronic lymphocytic leukemia, central nervous system (CNS) cancer (including brain), and malignant melanoma. METHODS Vital status was ascertained through 2008. Life table and Cox regression analyses were conducted. Cumulative exposure to cosmic radiation was estimated from work history data. RESULTS Compared to the U.S. general population, mortality from all causes, all cancer, and cardiovascular diseases was decreased, but mortality from aircraft accidents was highly elevated. Mortality was elevated for malignant melanoma but not for non-chronic lymphocytic leukemia. CNS cancer mortality increased with an increase in cumulative radiation dose. CONCLUSIONS Cockpit crew had a low all-cause, all-cancer, and cardiovascular disease mortality but elevated aircraft accident mortality. Further studies are needed to clarify the risk of CNS and other radiation-associated cancers in relation to cosmic radiation and other workplace exposures.

Abstract 2812: Chromosome translocation frequency and intakes of B vitamins, meat, and grain products in airline pilots

B vitamins such as folate and vitamins B2, B6, and B12 are essential for the maintenance of DNA integrity. Deficiency in these B vitamins can result in DNA strand breaks which, if unrepaired, can lead to the formation of chromosome aberrations (CA). Niacin also contributes to chromosome stability due to several important roles, including DNA repair and regulation of cell division and apoptosis. Animal and in vitro studies suggest that these B vitamins may protect against chromosome damage induced by ionizing radiation (IR), but data from IR-exposed human populations are limited. Airline pilots are exposed to cosmic IR, an efficient inducer of CA which have been shown to be associated with increased cancer risk. We examined the association between the frequency of translocations (stable form of CA) and intakes of these B vitamins and their food sources in 82 male airline pilots. All subjects completed a self-administered questionnaire with information on occupational history and lifestyle factors. Dietary vitamin B intakes were estimated using a validated semiquantitative food-frequency questionnaire and were energy-adjusted. Translocations were scored in an average of 1039 cell equivalents (CE) per subject using fluorescence in situ hybridization with whole chromosome paints, and expressed per 100 CE. Negative binomial regression was used to estimate rate ratios (RR) and 95% confidence intervals (CI), adjusted for age, flight experience in years, self-reported personal diagnostic X-ray procedures, military service, and lifestyle factors. We observed a significant inverse association between the frequency of translocations and intake of niacin from food: adjusted RR (95% CI) for subjects in the highest compared with lowest tertile was 0.58 (0.40, 0.83). Translocation frequency was not associated with total niacin intake from food and supplements, nor was it associated with intakes of folate, or vitamin B2, B6, or B12 either from food or from food and supplements. These results remained unchanged after further adjustment for the combined intakes of vitamins C and E, β-carotene, β-cryptoxanthin, and lutein-zeaxanthin from food (previously shown to be significantly and inversely associated with translocation frequency), or multivitamin supplement use. Additionally, the adjusted RR (95% CI) for ≥ median compared with Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2812.