Shift Work and Prostate Cancer Incidence in Industrial Workers: A Historical Cohort Study in a German Chemical Company

Risk of prostate cancer with increasing years of night shift work: A two-stage dose-response meta-analysis with duration of night shift work as exposure dose

Introduction

Night shift work could be a modifiable risk factor for prostate cancer. However, the epidemiological evidence is inconsistent. To summarize the existing evidence on this topic, we conducted a two-stage dose-response meta-analysis.

Methods

Medical librarians searched PubMed, EMBASE, and the Cochrane Library on December 30, 2022. Seven criteria were used to determine the inclusion of each study in the present analysis.

Results

Eleven cohort studies (12 cohort reports; total cases: 9366; and total person-years: 88,238,009) and seven case-control studies (seven case-control reports; total cases: 5593; and total controls: 6876) were included. This study estimated that the risk of prostate cancer increased by 1, 12, 24, and 39% after 1, 10, 20, and 30 years of night shift work exposure, respectively, according to four cohort and five case-control studies.

Discussion

Seven inclusion criteria were used to determine which studies were eligible for this analysis. Risk ratios from cohort studies and odds ratios from case-control studies were analyzed separately. However, all odds ratios from the case-control studies were excluded because of a high likelihood of publication bias. Moreover, exposure, measured in years of night shift work, was defined based on the information provided by individual studies. Finally, we utilized a recently reported two-stage dose-response meta-analysis method. This study provides evidence that night shift work contributes to the risk of prostate cancer in a dose-dependent manner.

Prostate cancer in workers exposed to night-shift work: two cases recognized by the Korean Epidemiologic Investigation Evaluation Committee

Background

In 2019, the International Agency for Research on Cancer re-evaluated the carcinogenicity of night-shift work and reported that there is limited evidence that night-shift work is carcinogenic for the development of prostate cancer. Therefore, in 2020 and 2021, the Korean Epidemiologic Investigation Evaluation Committee concluded that 2 cases of prostate cancer were occupational diseases related to the night-shift work. Here, we report the 2 cases of prostate cancer in night-shift workers which were first concluded as occupational diseases by the Korean Epidemiologic Investigation Evaluation Committee.

Case presentation

Patient A: A 61-year-old man worked as a city bus driver for approximately 17 years, from 2002 to 2019, and was exposed to night-shift work during this period. In March 2017, the patient was diagnosed with high-grade prostate cancer through core-needle biopsy after experiencing stinging pain lasting for 2 months. Patient B: A 56-year-old man worked as an electrician and an automated equipment operator in a cement manufacturing plant for 35 years from 1976 to 2013 and was exposed to night-shift work during this period. In 2013, the patient was diagnosed with high-grade prostate cancer through core needle biopsy at a university hospital because of dysuria that lasted for 6 months.

Conclusions

The 2 workers were diagnosed with high-grade prostate cancer after working night shifts for 17 and 35 years respectively. Additionally, previous studies have reported that high-grade prostate cancer has a stronger relationship with night-shift work than low or medium-grade prostate cancer. Therefore, the Korean Epidemiologic Investigation Evaluation Committee concluded that night-shift work in these 2 patients contributed to the development of their prostate cancer.

A broken circadian clock: The emerging neuro-immune link connecting depression to cancer

Circadian clocks orchestrate daily rhythms in many organisms and are essential for optimal health. Circadian rhythm disrupting events, such as jet-lag, shift-work, night-light exposure and clock gene alterations, give rise to pathologic conditions that include cancer and clinical depression. This review systemically describes the fundamental mechanisms of circadian clocks and the interacting relationships among a broken circadian clock, cancer and depression. We propose that this broken clock is an emerging link that connects depression and cancer development. Importantly, broken circadian clocks, cancer and depression form a vicious feedback loop that threatens systemic fitness. Arresting this harmful loop by restoring normal circadian rhythms is a potential therapeutic strategy for treating both cancer and depression.

Association Between Night-Shift Work and Cancer Risk: Updated Systematic Review and Meta-Analysis

Background: Nightshift work introduces light at night and causes circadian rhythm among night workers, who are considered to be at increased risk of cancer. However, in the last 2 years, nine population-based studies reported insignificant associations between night-shift work and cancer risks. We aimed to conduct an updated systematic review and meta-analysis to ascertain the effect of night-shift work on the incidence of cancers. Methods: Our protocol was registered in PROSPERO and complied with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Embase, PubMed, and Web of Science databases were used to comprehensively search studies published up to May 31, 2019. The random-effect model (Der Simonian-Laird method) was carried out to combine the risk estimates of night-shift work for cancers. The dose-response meta-analysis was performed to verify whether the association was in a dose-dependent manner. Results: Our literature searching retrieved 1,660 publications. Included in the meta-analyses were 57 eligible studies with 8,477,849 participants (mean age 55 years; 2,560,886 men, 4,220,154 women, and 1,696,809 not mentioned). The pooled results showed that night-shift work was not associated with the risk of breast cancer (OR = 1.009, 95% CI = 0.984-1.033), prostate cancer (OR = 1.027, 95% CI = 0.982-1.071), ovarian cancer (OR = 1.027, 95% CI = 0.942-1.113), pancreatic cancer (OR = 1.007, 95% CI = 0.910-1.104), colorectal cancer (OR = 1.016, 95% CI = 0.964-1.068), non-Hodgkin's lymph (OR = 1.046, 95% CI = 0.994-1.098), and stomach cancer (OR = 1.064, 95% CI = 0.971-1.157), while night-shift work was associated with a reduction of lung cancer (OR = 0.949, 95% CI = 0.903-0.996), and skin cancer (OR = 0.916, 95% CI = 0.879-0.953). The dose-response meta-analysis found that cancer risk was not significantly elevated with the increased light exposure of night- shift work. Conclusion: This systematic review of 57 observational studies did not find an overall association between ever-exposure to night-shift work and the risk of breast, prostate ovarian, pancreatic, colorectal, non-Hodgkin's lymph, and stomach cancers.

Shift Work and Prostate Cancer: An Updated Systematic Review and Meta-Analysis

The International Agency of Research in Cancer (IARC) has recently confirmed shift work as a type 2A carcinogen. The results presented in published epidemiological studies regarding prostate cancer are inconsistent and the association remains controversial. The aims of this study were: (a) to investigate the possible association between shift work and prostate cancer incidence, identifying possible sources of heterogeneity; and (b) to analyze the potential effect of publication bias. A search for cohort and case-control studies published from January 1980 to November 2019 was conducted. The quality of the articles was assessed using the Newcastle-Ottawa Scale. Pooled OR were calculated using random-effects models. Heterogeneity was evaluated using Cochran's Q test and data were stratified by potential sources of heterogeneity. Publication bias was analyzed. Eighteen studies were included. No association was found between rotating/night-shift work and prostate cancer, pooled OR 1.07 (95%CI 0.99 to 1.15), I2 = 45.7%, p = 0.016. Heterogeneity was eliminated when only cohort studies (pooled OR 1.03; 95%CI 0.96 to 1.10; I2 = 18.9%, p = 0.264) or high-quality studies (pooled OR 0.99; 95%CI 0.89 to 1.08; I2 = 0.0%, p = 0.571) were considered. A publication bias was detected. An association between shift work and prostate cancer cannot be confirmed with the available current data. Future analytical studies assessing more objective homogeneous exposure variables still seem necessary.

Night-Shift Work and Risk of Prostate Cancer: Results From a Canadian Case-Control Study, the Prostate Cancer and Environment Study

Night-shift work involving disruption of circadian rhythms has been associated with breast cancer risk. A role in prostate cancer is also suspected, but evidence is limited. We investigated the association between night-shift work and prostate cancer incidence in the Prostate Cancer and Environment Study (PROtEuS), a population-based case-control study conducted in 2005-2012 in Montreal, Quebec, Canada. Participants were 1,904 prostate cancer cases (432 high-grade cancers) and 1,965 population controls. Detailed work schedules for each job held for at least 2 years (n = 15,724) were elicited in face-to-face interviews. Night-shift work was defined as having ever worked ≥3 hours between midnight and 5:00 am ≥3 nights/month for ≥1 year. Unconditional logistic regression was used to estimate odds ratios and 95% confidence intervals for the association between night-shift work and prostate cancer, adjusting for age, ancestry, and education. No association was found between overall prostate cancer and night-shift work metrics, including ever exposure, duration, intensity, cumulative exposure, rotating shifts, and early-morning shifts. For none of the exposure indices was there evidence of heterogeneity in odds ratios between low- and high-grade cancers. Sensitivity analyses restricting exposures to ≥7 nights/month or considering screening history yielded similar results. Our findings lend no support for a major role of night-shift work in prostate cancer development.

Sex Differences in the Association between Night Shift Work and the Risk of Cancers: A Meta-Analysis of 57 Articles

Objectives

To identify the association between night shift work and the risk of various cancers with a comprehensive perspective and to explore sex differences in this association.

Methods

We searched PubMed, Embase, and Web of Science for studies on the effect of night shift work on cancer, including case-control, cohort, and nested case-control studies. We computed risk estimates with 95% confidence intervals (CIs) in a random or fixed effects model and quantified heterogeneity using the I ² statistic. Subgroup, metaregression, and sensitivity analyses were performed to explore potential sources of heterogeneity. Contour-enhanced funnel plots and the trim and fill method were used together to analyze bias. Linear dose-response analysis was used to quantitatively estimate the accumulative effect of night shift work on the risk of cancer.

Results

Fifty-eight studies were eligible for our meta-analysis, including 5,143,838 participants. In the random effects model, the pooled odds ratio (OR) of cancers was 1.15 (95% CI = 1.08-1.22, P < 0.001; I ² = 76.2%). Night shift work increased the cancer risk in both men (OR = 1.14, 95% CI = 1.05-1.25, P = 0.003) and women (OR = 1.12, 95% CI = 1.04-1.20, P = 0.002). Subgroup analyses showed that night shift work positively increased the risk of breast (OR = 1.22, 95% CI = 1.08-1.38), prostate (OR = 1.26, 95% CI = 1.05-1.52), and digestive system (OR = 1.15, 95% CI = 1.01-1.32) cancers. For every 5 years of night shift work, the cancer risk increased by 3.2% (OR = 1.032, 95% CI = 1.013-1.051).

Conclusion

This is the first meta-analysis identifying the positive association between night shift work and the risk of cancer and verifying that there is no sex difference in the effect of night shift work on cancer risk. Cancer risk increases with cumulative years of night shift work.

The Effect of Shift Work on Urogenital Disease: a Systematic Review

PURPOSE OF REVIEW

Non-standard shift work schedules negatively impact the overall health of shift workers, and several studies have shown that shift work, specifically, is detrimental to urogenital health. The aims of this study are to systematically review the literature and determine the effect of shift work on the outcomes of hypogonadism, male infertility, lower urinary tract symptoms, and urogenital cancers.

RECENT FINDINGS

Recent evidence supports associations between non-standard shift work and an increase in the frequency of prostate cancer and the severity of erectile dysfunction, lower urinary tract symptoms, and hypogonadal symptoms, as well as worsening of semen parameters and fertility. These associations are strengthened by the presence of shift work sleep disorder (SWSD) which affects up to 20% of shift workers. No studies have assessed the impact of shift work on the frequency or severity of nephrolithiasis, interstitial cystitis, pelvic pain, prostatitis, or urinary tract infections. Non-standard shift work has been associated with a variety of negative health outcomes and urologic complications, especially with concurrent shift work sleep disorder. Recognition of these elevated risks among shift workers can aid in more effective screening for urologic conditions.

Shift work, night work, and the risk of prostate cancer: A meta-analysis based on 9 cohort studies

BACKGROUND

Epidemiology studies suggested that shift work or night work may be linked to prostate cancer (PCa); the relationship, however, remains controversy.

METHODS

PubMed, ScienceDirect, and Embase (Ovid) databases were searched before (started from the building of the databases) February 4, 2017 for eligible cohort studies. We pooled the evidence included by a random- or fixed-effect model, according to the heterogeneity. A predefined subgroup analysis was conducted to see the potential discrepancy between groups. Sensitivity analysis was used to test whether our results were stale.

RESULTS

Nine cohort studies were eligible for meta-analysis with 2,570,790 male subjects. Our meta-analysis showed that, under the fixed-effect model, the pooled relevant risk (RR) of PCa was 1.05 (95% confidence interval [CI]: 1.00, 1.11; P = .06; I = 24.00%) for men who had ever engaged in night shift work; and under the random-effect model, the pooled RR was 1.08 (0.99, 1.17; P = .08; I = 24.00%). Subgroup analysis showed the RR of PCa among males in western countries was 1.05 (95% CI: 0.99, 1.11; P = .09; I = 0.00%), while among Asian countries it was 2.45 (95% CI: 1.19, 5.04; P = .02; I = 0.00%); and the RR was 1.04 (95% CI: 0.95, 1.14; P = .40; I = 29.20%) for the high-quality group compared with 1.21 (95% CI: 1.03, 1.41; P = .02; I = 0.00%) for the moderate/low-quality group. Sensitivity analysis showed robust results.

CONCLUSIONS

Based on the current evidence of cohort studies, we found no obvious association between night shift work and PCa. However, our subgroup analysis suggests that night shift work may increase the risk of PCa in Asian men. Some evidence of a small study effect was observed in this meta-analysis.

Can yesterday's smoking research inform today's shiftwork research? Epistemological consequences for exposures and doses due to circadian disruption at and off work

In 1950, landmark epidemiology studies by Wynder & Graham and Doll & Hill contributed to identifying smoking as a potent carcinogen. In 2007, IARC classified shiftwork involving circadian disruption (CD) as probably carcinogenic; however, epidemiological evidence in regards to the carcinogenicity of shiftwork that involves nightwork is conflicting. We hypothesize that shiftwork research is lacking chronobiological and methodological rigor and that lessons can be learned from comparison with smoking research. Herein, we provide a factual view at, and a fictional case study of, 1940s smoking research which serves as an analogy for current shiftwork research dilemmas. This analogy takes the form of limiting counting cigarettes to a particular time window (i.e. at work) rather than assessing exposures to, and doses of, accumulated smoking over 24 h, highlighting the importance of exposure and dose. Simply put, smoking insights could have been delayed or even disallowed. In conclusion, CD may be similar to smoking insofar as for quantitative measures of cumulative doses, exposures both at and off work may have to be considered. Future work must explore whether such similarity factually exists and whether CD is a cancer hazard in IARC terms.