Occupational exposure to carcinogenic substances in night versus day shift jobs

Our plain-English summary of Occupational exposure to carcinogenic substances in night versus day shift jobs, by J. Parks, U. Zanif, P. Bhatti (Scandinavian Journal of Work, Environment & Health, 2026).

The study

• Authors: J. Parks, U. Zanif, P. Bhatti
• Journal: Scandinavian Journal of Work, Environment & Health
• Published: 2026;52(4):434-441
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: This study aimed to determine whether night shift work was associated with exposure to carcinogenic hazards, independent of occupation and industry.

Methods: We conducted a cross-sectional analysis of 16 250 job records reported by 7023 participants. Participants provided lifetime job histories, including shift schedules and exposures to hazardous agents. Carcinogenic agents included established carcinogens classified by the International Agency for Research on Cancer, as well as broader exposure categories that may potentially contain carcinogenic constituents. Jobs involving ≥1 and ≥7 night shifts/month were compared with day-shift jobs. Occupations and industries were coded using National Occupational Classification (2016) and North American Industry Classification System (2017) codes. Generalized linear mixed models with random intercepts for participant, occupation code (2-digit level), and industry code (2-digit level) were used to estimate odds ratios (OR) for exposures associated with night- versus day-shift work, adjusting for biological sex and job start year.

Results: Night shifts were associated with greater odds of any hazardous exposure [≥1 night shift/month: OR 3.1, 95% confidence interval (CI) 2.6-3.8; ≥7 night shifts/month: OR 3.1, 95% CI 2.5-3.8]. Significant associations were observed for multiple agents, including asbestos, degreasing agents, diesel engine exhaust, gasoline engine exhaust, ionizing radiation, mineral/cutting/lubricating oil, paints/stains/varnish, welding fume, and wood dust.

Conclusions: Night-shift work was associated with an increased likelihood of self-reported exposure to multiple potentially carcinogenic agents, independent of broad occupational and industry groupings. Future research with more granular task-level information and quantitative exposure assessment will be important for clarifying the mechanisms underlying these differences.

In plain English

This cross-sectional study used lifetime job histories from the BC Generations Project, a population-based cohort of adults in British Columbia, Canada. For each job, participants reported their shift schedule and whether they had ever been exposed to a list of potentially carcinogenic agents, including asbestos. The authors analysed 16 250 job records from 7023 participants: all 11 250 jobs with at least one night shift per month and a random sample of 5000 day shift jobs. Exposure to at least one listed agent was reported for 31.9% of these night shift jobs and 12.1% of day shift jobs. For asbestos the figures were 7.2% and 1.5%. After adjustment for sex, job start year, occupation and industry, night shift jobs had higher odds of any reported exposure (OR 3.1, 95% CI 2.6–3.8). For asbestos, jobs with at least seven night shifts per month had a fully adjusted OR of 3.8 (95% CI 1.3–11.1). The authors concluded that night shift work was associated with an increased likelihood of self-reported exposure to multiple potentially carcinogenic agents. They noted that exposures were self-reported, reflected likelihood rather than dose, and that residual confounding remained possible.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional analysis of job records from a population-based cohort, using generalized linear mixed models
• Who was studied: 16 250 job records from 7023 participants in the BC Generations Project, a cohort of adults aged 35–69 at enrollment in 2009–2016 in British Columbia, Canada. The participants completed an online occupational history questionnaire in 2018. The records were all 11 250 jobs with at least 1 night shift per month plus a random sample of 5000 day shift jobs. 63% of participants were female.
• Exposure: The exposure of interest was night shift work: jobs with at least 1, and at least 7, night shifts per month, compared with day shift jobs. The outcomes were self-reported ever-exposure, per job, to listed potentially carcinogenic agents. These included asbestos (fiber type not specified), benzene, diesel and gasoline engine exhaust, ionizing radiation, welding fumes, wood dust and others.
• Main results:
  • Exposure to at least one potentially carcinogenic agent was reported for 31.9% of jobs with at least 1 night shift per month, 35.7% of jobs with at least 7 night shifts per month, and 12.1% of day shift jobs.
  • After adjustment for sex, job start year, industry and occupation, the odds of any reported exposure were elevated compared with day shift jobs. For jobs with at least 1 night shift per month the OR was 3.1 (95% CI 2.6–3.8). For jobs with at least 7 night shifts per month the OR was 3.1 (95% CI 2.5–3.8).
  • Asbestos exposure was reported for 1.5% of day shift jobs, 7.2% of jobs with at least 1 night shift per month, and 8.3% of jobs with at least 7 night shifts per month.
  • Odds of reported asbestos exposure were elevated for night shift jobs. The text and Table 3 agree on two estimates: for jobs with at least 1 night shift per month, the OR adjusted for sex and start year was 4.2 (95% CI 1.8–9.8); for jobs with at least 7 night shifts per month, the fully adjusted OR was 3.8 (95% CI 1.3–11.1). They disagree on the other two: the text gives a fully adjusted OR of 4.4 (95% CI 1.7–11.4) for at least 1 night shift per month and a minimally adjusted OR of 6.2 (95% CI 2.4–16.0) for at least 7 night shifts per month, while Table 3 places these two figures the other way round.
  • The strongest associations were for ionizing radiation. Fully adjusted ORs were 9.3 (95% CI 3.5–24.9) for jobs with at least 1 night shift per month and 6.7 (95% CI 1.5–29.5) for jobs with at least 7 night shifts per month.
  • No statistically significant associations were found for benzene, glues, herbicides/insecticides/fungicides, or pressure-treated wood. Associations for coal tar/soot/pitch/asphalt/creosote were no longer statistically significant after adjustment for industry and occupation.
  • The number of distinct reported exposures per job was higher for night shift jobs after full adjustment. The exposure count ratio was 2.2 (95% CI 1.9–2.5) for at least 1 night shift per month and 2.0 (95% CI 1.8–2.4) for at least 7 night shifts per month.
  • After adjustment for industry and occupation, the authors found no compelling evidence that odds of exposure increased with more frequent night shifts.
• The authors' conclusion: The authors concluded that night shift work was associated with an increased likelihood of self-reported exposure to multiple potentially carcinogenic agents, independent of broad occupational and industry groupings. They called for future research with task-level information and quantitative exposure assessment.
• Limitations the authors state:
  • Exposure data were self-reported and not externally validated, so misclassification or underreporting was possible.
  • Exposure timing could not be linked to shift, because exposures were reported for the job as a whole and many jobs had mixed schedules.
  • The findings reflect the likelihood of reported exposure, not exposure intensity or cumulative dose, and say nothing about health effects.
  • Some agents were reported by few jobs, which limited statistical power.
  • Residual confounding was possible, because the broad 2-digit occupation codes may group together workers with different responsibilities.
  • Differences in workplace organization and supervision between day and night shifts may have affected workers' awareness and reporting of exposures.
  • The results reflect British Columbia's historical and regulatory context and may not generalize to other regions or to more recent workforces.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Carcinogenic, Odds Ratio, confidence interval.

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