Firefighting and Cancer: A Meta-analysis of Cohort Studies in the Context of Cancer Hazard Identification.

Objective: We performed a meta-analysis of epidemiological results for the association between occupational exposure as a firefighter and cancer as part of the broader evidence synthesis work of the IARCMonographs program. Methods: A systematic literature search was conducted to identify cohort studies of firefighters followed for cancer incidence and mortality. Studies were evaluated for the influence of key biases on results. Random-effects meta-analysis models were used to estimate the association between ever-employment and duration of employment as a firefighter and risk of 12 selected cancers. The impact of bias was explored in sensitivity analyses. Results: Among the 16 included cancer incidence studies, the estimated meta-rate ratio, 95% confidence interval (CI), and heterogeneity statistic (I2) for ever-employment as a career firefighter compared mostly to general populations were 1.58 (1.14-2.20, 8%) for mesothelioma, 1.16 (1.08-1.26, 0%) for bladder cancer, 1.21 (1.12-1.32, 81%) for prostate cancer, 1.37 (1.03-1.82, 56%) for testicular cancer, 1.19 (1.07-1.32, 37%) for colon cancer, 1.36 (1.15-1.62, 83%) for melanoma, 1.12 (1.01-1.25, 0%) for non-Hodgkin lymphoma, 1.28 (1.02-1.61, 40%) for thyroid cancer, and 1.09 (0.92-1.29, 55%) for kidney cancer. Ever-employment as a firefighter was not positively associated with lung, nervous system, or stomach cancer. Results for mesothelioma and bladder cancer exhibited low heterogeneity and were largely robust across sensitivity analyses. Conclusions: There is epidemiological evidence to support a causal relationship between occupational exposure as a firefighter and certain cancers. Challenges persist in the body of evidence related to the quality of exposure assessment, confounding, and medical surveillance bias.

Prevalence and risk factors for silicosis among a large cohort of stone benchtop industry workers.

OBJECTIVES: High silica content artificial stone has been found to be associated with silicosis among stone benchtop industry (SBI) workers. The objectives of this study were to determine the prevalence of and risk factors for silicosis among a large cohort of screened SBI workers, and determine the reliability of respiratory function testing (RFT) and chest x-ray (CXR) as screening tests in this industry. METHODS: Subjects were recruited from a health screening programme available to all SBI workers in Victoria, Australia. Workers undertook primary screening, including an International Labour Office (ILO) classified CXR, and subject to prespecified criteria, also underwent secondary screening including high-resolution CT (HRCT) chest and respiratory physician assessment. RESULTS: Among 544 SBI workers screened, 95% worked with artificial stone and 86.2% were exposed to dry processing of stone. Seventy-six per cent (414) required secondary screening, among whom 117 (28.2%) were diagnosed with silicosis (median age at diagnosis 42.1 years (IQR 34.8-49.7)), and all were male. In secondary screening, silicosis was associated with longer SBI career duration (12 vs 8 years), older age, lower body mass index and smoking. In those with silicosis, forced vital capacity was below the lower limit of normal in only 14% and diffusion capacity for carbon monoxide in 13%. Thirty-six (39.6%) of those with simple silicosis on chest HRCT had an ILO category 0 CXR. CONCLUSION: Screening this large cohort of SBI workers identified exposure to dry processing of stone was common and the prevalence of silicosis was high. Compared with HRCT chest, CXR and RFTs had limited value in screening this high-risk population.

The carcinogenicity of opium consumption: a systematic review and meta-analysis.

The carcinogenicity of opium consumption was recently evaluated by a Working Group convened by the International Agency for Research on Cancer (IARC). We supplement the recent IARC evaluation by conducting an extended systematic review as well as a quantitative meta-analytic assessment of the role of opium consumption and risk for selected cancers, evaluating in detail various aspects of study quality on meta-analytic findings. We searched the published literature to identify all relevant studies on opium consumption and risk of selected cancers in humans through 31 October, 2022. Meta-relative risks (mRRs) and associated 95% confidence intervals (CIs) were estimated using random-effects models for studies of cancer of the urinary bladder, larynx, lung, oesophagus, pancreas, and stomach. Heterogeneity among studies was assessed using the I2 statistic. We assessed study quality and conducted sensitivity analyses to evaluate the impact of potential reverse causation, protopathic bias, selection bias, information bias, and confounding. In total, 2 prospective cohort studies and 33 case-control studies were included. The overall pooled mRR estimated for 'ever or regular' versus 'never' use of opium ranged from 1.50 (95% CI 1.13-1.99, I2 = 0%, 6 studies) for oesophageal cancer to 7.97 (95% CI 4.79-13.3, I2 = 62%, 7 studies) for laryngeal cancer. Analyses of cumulative opium exposure suggested greater risk of cancer associated with higher opium consumption. Findings were robust in sensitivity analyses excluding studies prone to potential methodological sources of biases and confounding. Findings support an adverse association between opium consumption and cancers of the urinary bladder, larynx, lung, oesophagus, pancreas and stomach.

Predictors of psychological stress in silica-exposed workers in the artificial stone benchtop industry.

BACKGROUND AND OBJECTIVE: Artificial stone benchtops are a popular kitchen product, but dust from their preparation and installation contains respirable crystalline silica, which causes silicosis. Silicosis is a preventable, permanent lung disease. The aim of this study was to assess mental health in workers from the artificial stone benchtop industry at risk of silicosis. METHODS: Workers from the artificial stone benchtop industry undergoing assessment for silica-associated disease were included. Information on demographics; occupational, medical and smoking history; modified Medical Research Council dyspnoea scale; Perceived Stress Scale (PSS-10) questionnaire; spirometry; and chest x-ray was collected. Univariate and multivariate regression analyses were conducted. RESULTS: Of the 547 participants, the majority were men, aged under 45 years, in the industry for less than 10 years. With each increase of dyspnoea score, PSS-10 scores increased. Higher PSS-10 scores were also observed in those no longer in the industry, with a history of anxiety or depression, attending assessment early in the programme and a medium exposure duration. Participants who used an interpreter reported lower stress. No difference was observed across job title, age, sex, smoking, spirometry or chest x-ray categories after multivariate analysis. CONCLUSION: This study identified workers with dyspnoea as likely to report higher stress. Other factors, such as leaving the industry, early attendance and a history of anxiety or depression, are also helpful in identifying workers at risk of poorer mental health outcomes.

Cancer and mortality in coal mine workers: a systematic review and meta-analysis.

Coal mine workers are exposed to a number of workplace hazards which may increase the risk of cancer and mortality. We conducted a systematic review and meta-analysis to investigate cancer and mortality in coal mine workers We searched in Ovid Medline, PubMed, Embase and Web of Science databases using keywords and text words related to coal mines, cancer and mortality and identified 36 full-text articles using predefined inclusion criteria. Each study's quality was assessed using the Newcastle-Ottawa Scale. We performed random-effect meta-analyses including 21 of the identified articles evaluating cancer and/or mortality of coal mine workers. The meta-analysis showed an increased risk of all-cause mortality (SMR 1.14, 95% CI 1.00 to 1.30) and mortality from non-malignant respiratory disease (NMRD) (3.59, 95% CI 3.00 to 4.30) in cohorts with coal workers' pneumoconiosis (CWP). We found a somewhat increased risk of stomach cancer (1.11, 95% CI 0.97 to 1.35) and of mortality from NMRD (1.26, 95% CI 0.99 to 1.61) in the cohorts of coal miners with unknown CWP status. The meta-analysis also showed a decreased risk of prostate cancer and cardiovascular and cerebrovascular mortality among coal miners. This may be a result of the healthy worker effect and possible lower smoking rates, and perhaps also reflect the physically active nature of many jobs in coal mines. The meta-analysis for lung cancer did not show increased risk in coal miners with CWP (1.49, 95% CI 0.70 to 3.18) or for coal miners of unknown CWP status (1.03, 95% CI 0.91 to 1.18). Lower smoking rates in coal mine workers could explain why case-control studies where smoking was controlled for showed higher risks for lung cancer than were seen in cohort studies. Coal mine workers are at increased risk of mortality from NMRD but decreased risk of prostate cancer and cardiovascular and cerebrovascular mortality. Studies of coal mine workers need long-term follow-up to identify increased mortality and cancer incidence.

Are There Ethnic Disparities in Exposure to Workplace Hazards Among New Zealand Migrants to Australia?

Disparities in exposure to workplace hazards exist between Maori and non-Maori workers in New Zealand, with Maori workers generally incurring poorer conditions. This study aimed to determine if these ethnic disparities are similar after migration to Australia. A national cross-sectional telephone survey asked participants what tasks they undertook in their job to assess exposure to carcinogens as well as whether they experienced ethnic discrimination, bullying, job precariousness, or job strain. A total of 389 New Zealand Caucasians and 152 Maori/Pasifika workers were recruited. After adjustment, 79% of Maori/Pasifika compared with 67% of New Zealand Caucasian workers were assessed as being exposed to at least one carcinogen at work. Maori/Pasifika workers were also more likely to report ethnic discrimination and fair or poor current health than New Zealand Caucasians. Some ethnic disparities in exposure to workplace hazards in New Zealand are apparent after migration to Australia.

Occupational Asbestos Exposure and Kidney Cancer: Systematic Review and Meta-analysis of Cohort Studies.

OBJECTIVES: An estimated 125 million workers are exposed to asbestos worldwide. Asbestos is classified by the International Agency for Research on Cancer as a Group 1 carcinogen. The association between occupational asbestos exposure and kidney cancer is not well established however. This study aimed to determine the mortality and incidence of kidney cancer in workers who have been exposed to asbestos. We performed a systematic review and meta-analysis to evaluate the association between occupational asbestos exposure and kidney cancer. METHODS: Medline, EMBASE, and Web of Science were searched according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for articles on occupational asbestos exposure and kidney cancer. The studies reported the standardized mortality ratio (SMR) or standardized incidence ratio (SIR) of kidney cancer in workers exposed to asbestos. SMRs or SIRs with its 95% confidence interval (CI) were pooled using a fixed-effect model. RESULTS: Forty-nine cohort studies involving 335 492 workers were selected for analysis. These studies included 468 kidney cancer deaths and 160 incident cases. The overall pooled-SMR of kidney cancer was 0.95 (95% CI: 0.86-1.05), with no significant heterogeneity (PQ = 0.09, I2 = 24.87%). The overall pooled-SIR of kidney cancer was 0.95 (95% CI: 0.79-1.11), with no significant heterogeneity (PQ = 0.68, I2 = 0.00%). Subgroup analysis did not find any increased association with occupational asbestos exposure. There was no evidence of publication bias with Egger's test P values of 0.08 for mortality studies and 0.99 for incidence studies. CONCLUSIONS: This systematic review and meta-analysis did not show evidence of association between occupational asbestos exposure and kidney cancer mortality or incidence.

OccIDEAS: web-based assessment of occupational agent exposure.

Most epidemiological studies of disease aetiology do not consider potential risk factors at work. This may be because work is a complex exposure: people usually have a series of different jobs over their working lifetime; within each job there may be a range of different tasks; and there may be a variety of exposures in each job. Because of this complexity, many epidemiologists do not have the expertise or training to assess occupational exposures accurately. Our web-based application, OccIDEAS, manages the process of occupational agent assessment in epidemiological studies. The epidemiologist chooses the agents of interest for the study and OccIDEAS provides an online set of questionnaires that are tailored to those agents. The participant is asked specific questions about their job and evidence-based algorithms provide an assessment of exposure to each agent. OccIDEAS puts the world's best occupational epidemiological expertise within reach of any researcher.

Does exposure to workplace hazards cluster by occupational or sociodemographic characteristics? An analysis of foreign-born workers in Australia.

BACKGROUND: Disparities in exposure to occupational hazards may be linked to social position as well as the type of job a person holds. This study aimed to describe the prevalence of exposure to workplace hazards among three migrant worker groups and to assess whether social disparities in exposure for these groups remain after adjusting for occupational characteristics. METHODS: Data were collected in 2017/2018 from 1630 Australian workers born in New Zealand, India, and the Philippines. Weighted estimated prevalence of exposure to 10 carcinogens and four psychosocial hazards (discrimination, job strain, vulnerability, and insecurity) was calculated for sociodemographics and occupation. Regression estimated the likelihood of exposure by sociodemographics after adjustment for occupational characteristics. RESULTS: Exposure to workplace hazards ranged from 11.7% (discrimination) to 61.2% (exposed to at least one carcinogen). Compared with workers born in India, New Zealand born workers were over twice as likely to be exposed to diesel engine exhaust (adjusted odds ratio [aOR] = 2.60) and 60% more likely to be exposed to at least one carcinogen (aOR = 1.60) but less likely to be exposed to any psychosocial hazard. Social disparities by country of birth, sex, age, education, and number of years in Australia, as well as company size, employment type, and hours, worked remained associated with greater likelihood of reporting one or more workplace hazards after adjusting for occupational characteristics. CONCLUSION: Examining sociodemographic as well as occupational characteristics helps to clarify groups most likely to be exposed to workplace hazards who can be hidden when examining occupational characteristics alone.

The estimated prevalence of exposure to carcinogens, asthmagens, and ototoxic agents among healthcare workers in Australia.

BACKGROUND: Healthcare workers are occupationally exposed to various hazardous chemicals and agents that can potentially result in long-term adverse health effects. These exposures have not been comprehensively examined at a population level. The aim of this study was to examine occupational exposures to a wide range of asthmagens, carcinogens, and ototoxic agents among healthcare workers in Australia. METHODS: Data were collected as part of the Australian Work Exposures Studies, which were computer-assisted telephone surveys conducted in 2011, 2014, and 2016 to assess the prevalence of occupational exposures to carcinogens, asthmagens, and ototoxic agents, respectively, among Australian workers. Using data on healthcare workers, the prevalence of exposures to these agents was calculated and associations of demographic variables and occupation groups with exposure status were examined. RESULTS: The prevalence of exposure to at least one asthmagen, carcinogen, and ototoxic agent was 92.3%, 50.7%, and 44.6%, respectively. The most common exposures were to (a) cleaning and sterilizing agents in the asthmagen group; (b) shift work in the carcinogen group; and (c) toluene and p-xylene among ototoxic agents. Exposure varied by occupation, with exposure to carcinogens and ototoxic agents highest among personal carers and exposure to carcinogens most likely among nursing professionals and health and welfare support workers. CONCLUSION: The results demonstrate that a substantial proportion of Australian healthcare workers are occupationally exposed to asthmagens, carcinogens, and ototoxic agents. These exposures are more common among certain occupational groups. The information provided by this study will be useful in prioritizing and implementing control strategies.

Mortality and cancer incidence among female Australian firefighters.

OBJECTIVES: To investigate the mortality and cancer incidence of female firefighters, a group where there are limited published findings. METHODS: Participating fire agencies supplied records of individual firefighters including the number and type of incidents attended. The cohort was linked to the Australian National Death Index and Australian Cancer Database. Standardised mortality ratios and standardised cancer incidence ratios were calculated separately for paid and volunteer firefighters. Volunteer firefighters were grouped into tertiles by the duration of service and by a number of incidents attended and relative mortality ratios and relative incidence ratios calculated. RESULTS: For volunteer firefighters (n=37 962), the overall risk of mortality and risk from all major causes of death were reduced when compared with the general population whether or not they had ever attended incidents. Volunteer firefighters had a similar cancer incidence when compared with the general population for most major cancer categories. Female volunteer firefighters have usually attended few fires. Of those who had turned out to incidents, only one-third had attended more than 12 fires about half the number for male volunteers. Mortality and cancer incidence for paid female firefighters (n=1682) were similar to the general population but the numbers were small and so power was limited. CONCLUSIONS: Female volunteer firefighters have a cancer incidence similar to the general population but a reduced risk of mortality which is likely to be a result of a 'healthy volunteer' effect.Most of the paid female firefighters were relatively recent recruits and it will be important to monitor the health of this group as more women are recruited to front-line firefighting roles.

Exposure to noise and ototoxic chemicals in the Australian workforce.

OBJECTIVE: To determine the current prevalence of exposure to workplace noise and ototoxic chemicals, including co-exposures. METHOD: A cross-sectional telephone survey of nearly 5000 Australian workers was conducted using the web-based application, OccIDEAS. Participants were asked about workplace tasks they performed and predefined algorithms automatically assessed worker's likelihood of exposure to 10 known ototoxic chemicals as well as estimated their full shift noise exposure level (LAeq,8h) of their most recent working day. Results were extrapolated to represent the Australian working population using a raked weighting technique. RESULTS: In the Australian workforce, 19.5% of men and 2.8% of women exceeded the recommended full shift noise limit of 85 dBA during their last working day. Men were more likely to be exposed to noise if they were younger, had trade qualifications and did not live in a major city. Men were more likely exposed to workplace ototoxic chemicals (57.3%) than women (25.3%). Over 80% of workers who exceeded the full shift noise limit were also exposed to at least one ototoxic chemical in their workplace. CONCLUSION: The results demonstrate that exposures to hazardous noise and ototoxic chemicals are widespread in Australian workplaces and co-exposure is common. Occupational exposure occurs predominantly for men and could explain some of the discrepancies in hearing loss prevalence between genders.

Regulatory T cells mediate specific suppression by depleting peptide-MHC class II from dendritic cells.

Regulatory T cells (Treg cells) can activate multiple suppressive mechanisms in vitro after activation via the T cell antigen receptor, resulting in antigen-independent suppression. However, it remains unclear whether similar pathways operate in vivo. Here we found that antigen-specific Treg cells activated by dendritic cells (DCs) pulsed with two antigens suppressed conventional naive T cells (Tnaive cells) specific for both cognate antigens and non-cognate antigens in vitro but suppressed only Tnaive cells specific for cognate antigen in vivo. Antigen-specific Treg cells formed strong interactions with DCs, resulting in selective inhibition of the binding of Tnaive cells to cognate antigen yet allowing bystander Tnaive cell access. Strong binding resulted in the removal of the complex of cognate peptide and major histocompatibility complex class II (pMHCII) from the DC surface, reducing the capacity of DCs to present antigen. The enhanced binding of Treg cells to DCs, coupled with their capacity to deplete pMHCII, represents a novel pathway for Treg cell-mediated suppression and may be a mechanism by which Treg cells maintain immune homeostasis.

Interventions to Reduce Future Cancer Incidence from Diesel Engine Exhaust: What Might Work?

Exposure to diesel engine exhaust (DEE) contributes appreciably to the burden of occupational cancer. This study aims to estimate the potential impact of a range of interventions on the future burden of cancer from occupational exposure to DEE in Australia. The future excess fraction method, a novel method based on the lifetime risk approach, was used to model changes in the future burden of cancer among the Australian working age population exposed to DEE at work in 2012 under various intervention strategies. The interventions modeled were based on the widely accepted hierarchy of control model. At baseline, 600 (0.4%) future bladder and 4,450 (0.6%) future lung cancer cases over the lifetime of the cohort were estimated to be attributable to occupational exposure to DEE in those exposed in 2012. Up to 2,000 of these cases were estimated to be avoidable through the use of various interventions. Exhaust hoses (engineering controls) were estimated to be particularly effective. This study provides an indication of which intervention strategies may be most useful in reducing the future burden of cancer associated with occupational DEE exposure. These results show the potential effect of changing current exposure, rather than focusing on past exposures, and thus provide relevant information for policy planning.

Prevalence of exposure to occupational carcinogens among farmers.

INTRODUCTION: Farmers experience a range of carcinogenic exposures, including some pesticides, fuels, engine exhausts, metals, some organic solvents, silica, wood dusts and solar radiation. However many studies investigating the risk of cancer in farmers focus on pesticide exposure alone. The aim of this study was to determine which carcinogens Australian farmers are exposed to, the prevalence and circumstances of those exposures, and the use of protective equipment. METHODS: The study used data from the Australian Work Exposures Study (AWES) a cross-sectional study conducted in 2012 that investigated the prevalence of carcinogen exposure among Australian workers. This was supplemented with data from AWES-Western Australia (WA), conducted in 2013, which followed the same methodology but in Western Australian workers only. A total of 5498 Australian workers were interviewed about the tasks they carry out in their workplace. The 166 participants who worked in farming (126 men and 40 women, with an age range of 18-65 years) are the focus of this article. RESULTS: On average, farmers had been exposed to five different carcinogens. Highest numbers of exposures occurred among men and those working on mixed crop and livestock farms. Solar radiation, diesel engine exhaust and certain solvents were the most prevalent exposures, each with over 85% of farmers exposed. The main tasks leading to exposure were working outdoors, using and repairing farming equipment and burning waste. Sun protection and closed cabs on machinery were the most frequently used forms of protection. CONCLUSIONS: Farmers are a high risk group in relation to carcinogen exposure. The variation in tasks that they undertake results in exposure to a wide variety of different carcinogens that require similarly varied control measures.

Type I interferon signaling attenuates regulatory T cell function in viral infection and in the tumor microenvironment.

Regulatory T cells (Tregs) play a cardinal role in the immune system by suppressing detrimental autoimmune responses, but their role in acute, chronic infectious diseases and tumor microenvironment remains unclear. We recently demonstrated that IFN-α/ß receptor (IFNAR) signaling promotes Treg function in autoimmunity. Here we dissected the functional role of IFNAR-signaling in Tregs using Treg-specific IFNAR deficient (IFNARfl/flxFoxp3YFP-Cre) mice in acute LCMV Armstrong, chronic Clone-13 viral infection, and in tumor models. In both viral infection and tumor models, IFNARfl/flxFoxp3YFP-Cre mice Tregs expressed enhanced Treg associated activation antigens. LCMV-specific CD8+ T cells and tumor infiltrating lymphocytes from IFNARfl/flxFoxp3YFP-Cre mice produced less antiviral and antitumor IFN-γ and TNF-α. In chronic viral model, the numbers of antiviral effector and memory CD8+ T cells were decreased in IFNARfl/flxFoxp3YFP-Cre mice and the effector CD4+ and CD8+ T cells exhibited a phenotype compatible with enhanced exhaustion. IFNARfl/flxFoxp3YFP-Cre mice cleared Armstrong infection normally, but had higher viral titers in sera, kidneys and lungs during chronic infection, and higher tumor burden than the WT controls. The enhanced activated phenotype was evident through transcriptome analysis of IFNARfl/flxFoxp3YFP-Cre mice Tregs during infection demonstrated differential expression of a unique gene signature characterized by elevated levels of genes involved in suppression and decreased levels of genes mediating apoptosis. Thus, IFN signaling in Tregs is beneficial to host resulting in a more effective antiviral response and augmented antitumor immunity.

Night shift work and breast cancer: a pooled analysis of population-based case-control studies with complete work history.

Night shift work has been suspected to increase breast cancer risk but epidemiological studies have been inconsistent due to heterogeneous assessment of exposure to night work. To overcome this limitation, we pooled data of five population-based case-control studies from Australia, Canada, France, Germany, and Spain into a single harmonized dataset using a common definition of night work including 6093 breast cancer cases and 6933 population controls. The odds ratio for breast cancer in women who ever worked at night for at least 3 h between midnight and 5 a.m. as compared to never night workers was 1.12 (95% CI 1.00-1.25). Among pre-menopausal women, this odds ratio was 1.26 [1.06-1.51], increasing to 1.36 [1.07-1.74] for night shifts ≥ 10 h, 1.80 [1.20-2.71] for work ≥ 3 nights/week, and 2.55 [1.03-6.30] for both duration of night work ≥ 10 years and exposure intensity ≥ 3 nights/week. Breast cancer risk in pre-menopausal women was higher in current or recent night workers (OR = 1.41 [1.06-1.88]) than in those who had stopped night work more than 2 years ago. Breast cancer in post-menopausal women was not associated with night work whatever the exposure metric. The increase in risk was restricted to ER+ tumors, particularly those who were both ER+ and HER2+ . These results support the hypothesis that night shift work increases the risk of breast cancer in pre-menopausal women, particularly those with high intensity and long duration of exposure. Risk difference between pre- and post-menopausal women deserves further scrutiny.

Shift work that involves circadian disruption and breast cancer: a first application of chronobiological theory and the consequent challenges.

OBJECTIVES: In 2007, the International Agency for Research on Cancer classified shift work involving circadian disruption (CD) as probably carcinogenic to humans. Circadian disruption could be conceptualised as the overlap of activity, such as work, with an individual's biological night. The latter can be approximated from a worker's chronotype (or morning/evening preference). Few previous studies have taken chronotype into account when assessing CD caused by shift work. Our objective was to test the hypothesis that women working during their biological night would be at increased risk of breast cancer. METHODS: We used data from our case-control study of breast cancer to investigate associations between shift work involving CD and breast cancer risks. Previously, we had assumed that everyone working in jobs which involved work for two or more shifts between midnight and 05:00 hours was equally exposed to CD. In the present analyses, we reclassified as unexposed those who had a late chronotype in which their preferred bedtime was 2 hours after the end of their shift. RESULTS: Only 30 of 1385 night jobs changed classification and the overall finding (OR 1.17, 95% CI 0.98 to 1.41) was not different to the original finding when chronotype was not considered. CONCLUSIONS: We found virtually no difference between our new and old classifications of exposure. However, we were not able to calculate the total number of chronodisrupted shifts over a lifetime in order to assess dose and nor were we able to determine how many women were exposed to CD when doing shifts which began before midnight. Our first practical application highlights challenges for future chronobiology-based research.