Shift work and cancer risk: Potential mechanistic roles of circadian disruption, light at night, and sleep deprivation

The circadian disruption in shift-workers is suggested to be a risk factor to develop overweight and metabolic dysfunction. The conflicting time signals given by shifted activity, shifted food intake and exposure to light at night occurring in the shift-worker are proposed to be the cause for the loss of internal synchrony and the consequent adverse effects on body weight and metabolism. Because food elicited signals have proven to be potent entraining signals for peripheral oscillations, here we review the findings from experimental models of shift-work and verify whether they provide evidence about the causal association between shifted feeding schedules, circadian disruption and altered metabolism. We found mainly four experimental models that mimic the conditions of shift-work: protocols of forced sleep deprivation, of forced activity during the normal rest phase, exposure to light at night and shifted food timing. A big variability in the intensity and duration of the protocols was observed, which led to a diversity of effects. A common result was the disruption of temporal patterns of activity; however, not all studies explored the temporal patterns of food intake. According to studies that evaluate time of food intake as an experimental model of shift-work and studies that evaluate shifted food consumption, time of food intake may be a determining factor for the loss of balance at the circadian and metabolic level.

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shift work, light at night, and breast cancer risk: a meta-analysis

ISEE Conference Abstracts ◽

10.1289/isee.2013.p-3-27-29 ◽

2013 ◽

Vol 2013 (1) ◽

pp. 4664

Author(s):

Chunla He ◽

Sonia Taj Anand ◽

Sara E Wagner

Keyword(s):

Breast Cancer ◽

Breast Cancer Risk ◽

Cancer Risk ◽

Shift Work ◽

Meta Analysis ◽

Light At Night

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Shift work and cancer

Russian Journal of Occupational Health and Industrial Ecology ◽

10.31089/1026-9428-2019-59-9-838-839 ◽

2020 ◽

pp. 838-838

Author(s):

M. C. Turner

Keyword(s):

General Population ◽

Shift Work ◽

Preventive Measures ◽

Night Shift ◽

Circadian Disruption ◽

Light Spectrum ◽

Light At Night ◽

Epidemiological Evidence ◽

Cardiometabolic Diseases ◽

Breast And Prostate Cancer

Circadian disruption and night-shift work have been associated with a range of acute and chronic health effects including cardiometabolic diseases, obesity, as well as breast and prostate cancer. Circadian disruption may also affect the health of the general population because of widespread mistimed lifestyle practices including mistimed eating and sleep patterns and increasing exposure to light-at-night and particularly blue light spectrum through the use of e-readers, LEDs and smartphones. New epidemiological evidence on the effects of circadian disruption and light-at-night in workers and the general population will be presented, and mechanisms of disease and potential preventive measures discussed.

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Measuring Light at Night and Melatonin Levels in Shift Workers: A Review of the Literature

Biological Research For Nursing ◽

10.1177/1099800417714069 ◽

2017 ◽

Vol 19 (4) ◽

pp. 365-374 ◽

Cited By ~ 25

Author(s):

Claudia M. Hunter ◽

Mariana G. Figueiro

Keyword(s):

Shift Work ◽

Quantitative Methods ◽

English Language ◽

Circadian Disruption ◽

Light At Night ◽

Shift Workers ◽

Pubmed Database ◽

Increased Risk ◽

Disease Risks ◽

Cancerous Cells

Shift work, especially that involving rotating and night shifts, is associated with an increased risk of diseases, including cancer. Attempts to explain the association between shift work and cancer in particular have focused on the processes of melatonin production and suppression. One hypothesis postulates that exposure to light at night (LAN) suppresses melatonin, whose production is known to slow the development of cancerous cells, while another proposes that circadian disruption associated with shift work, and not just LAN, increases health risks. This review focuses on six studies that employed quantitative measurement of LAN and melatonin levels to assess cancer risks in shift workers. These studies were identified via searching the PubMed database for peer-reviewed, English-language articles examining the links between shift work, LAN, and disease using the terms light at night, circadian disruption, health, risk, cancer, shift work, or rotating shift. While the results indicate a growing consensus on the relationship between disease risks (particularly cancer) and circadian disruption associated with shift work, the establishment of a direct link between LAN and disease has been impeded by contradictory studies and a lack of consistent, quantitative methods for measuring LAN in the research to date. Better protocols for assessing personal LAN exposure are required, particularly those employing calibrated devices that measure and sample exposure to workplace light conditions, to accurately assess LAN’s effects on the circadian system and disease. Other methodologies, such as measuring circadian disruption and melatonin levels in the field, may also help to resolve discrepancies in the findings.

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Association between light at night, melatonin secretion, sleep deprivation, and the internal clock: Health impacts and mechanisms of circadian disruption

Life Sciences ◽

10.1016/j.lfs.2017.02.008 ◽

2017 ◽

Vol 173 ◽

pp. 94-106 ◽

Cited By ~ 159

Author(s):

Yvan Touitou ◽

Alain Reinberg ◽

David Touitou

Keyword(s):

Sleep Deprivation ◽

Internal Clock ◽

Circadian Disruption ◽

Health Impacts ◽

Melatonin Secretion ◽

Light At Night

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Implications of Lifestyle and Occupational Factors on the Risk of Breast Cancer in Shiftwork Nurses

Healthcare ◽

10.3390/healthcare9060649 ◽

2021 ◽

Vol 9 (6) ◽

pp. 649

Author(s):

Javier Fagundo-Rivera ◽

Regina Allande-Cussó ◽

Mónica Ortega-Moreno ◽

Juan Jesús García-Iglesias ◽

Adolfo Romero ◽

...

Keyword(s):

Breast Cancer ◽

Shift Work ◽

Regression Tree ◽

Night Work ◽

Circadian Disruption ◽

Classification And Regression Tree ◽

Baseline Risk ◽

Unhealthy Lifestyle ◽

Cross Sectional ◽

Occupational Factors

Shift work that involves circadian disruption has been highlighted as a likely carcinogenic factor for breast cancer in humans. Also, unhealthy lifestyle habits observed in night work nurses could be causally related to an increase in the incidence of estrogen-positive breast tumours in this population. Assessing baseline risk of breast cancer in nurses is essential. The objective of this study was to analyze the risk of breast cancer that nurses had in relation to their lifestyle and labour factors related to shift work. A cross-sectional descriptive study through a questionnaire about sociodemographic variables, self-perception of health, and working life was designed. The sample consisted of 966 nurses. The relationship between variables was tested. A binary logistic regression and a classification and regression tree were performed. The most significant labour variables in relation to the risk of breast cancer were the number of years worked (more than 16 years; p < 0.01; OR = 8.733, 95% CI = 2.811, 27.134) and the total years performing more than 3 nights per month (10 or more years; p < 0.05; OR = 2.294, 95% CI = 1.008, 5.220). Also, the nights worked throughout life (over 500; OR = 4.190, 95% CI = 2.118, 8.287) were significant in the analysis. Nurses who had or ever had breast cancer valued their self-perceived health more negatively (p < 0.001) and referred a lower quality of sleep (p < 0.001) than the non-cases nurses. The occupational factors derived from night work could have several impacts on nurses’ health and their family-work balance. Promoting healthy lifestyles, informing about shift work risks, and adjusting shift work schedules are critical methods to decrease the possible effects of circadian disruption in nurses.

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Rotating Night-Shift Work and Lung Cancer Risk Among Female Nurses in the United States

American Journal of Epidemiology ◽

10.1093/aje/kwt155 ◽

2013 ◽

Vol 178 (9) ◽

pp. 1434-1441 ◽

Cited By ~ 46

Author(s):

E. S. Schernhammer ◽

D. Feskanich ◽

G. Liang ◽

J. Han

Keyword(s):

United States ◽

Lung Cancer ◽

Cancer Risk ◽

Shift Work ◽

Lung Cancer Risk ◽

Night Shift ◽

The United States ◽

Night Shift Work ◽

Female Nurses

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Is shift-work associated with increased risk of rectal cancer? A meta-analysis.

Journal of Clinical Oncology ◽

10.1200/jco.2021.39.15_suppl.e15600 ◽

2021 ◽

Vol 39 (15_suppl) ◽

pp. e15600-e15600

Author(s):

Chenyu Sun ◽

Ce Cheng ◽

Kelly Kozma ◽

Gopika Chandra ◽

Na Hyun Kim ◽

...

Keyword(s):

Rectal Cancer ◽

Cancer Risk ◽

Shift Work ◽

Meta Analysis ◽

Night Shift ◽

Fixed Effect Model ◽

Night Shift Work ◽

Increased Risk ◽

Rotating Shift Work ◽

Trim And Fill

e15600 Background: Globally, more than 1.8 million people were diagnosed of colorectal cancer (CRC) in 2018, with over 30% of CRC in the rectum. Shift-work, involving circadian disruption, sleep deprivation and lifestyle changes, was designated as a probable cause of cancer by The International Agency for Research on Cancer. Previous studies investigating the impact of permanent night-shift work and rotating shift-work on rectal cancer risk showed controversial results. Thus, this meta-analysis was conducted. Methods: A comprehensive literature search on PubMed was conducted to identify all relevant studies published prior to January 2021 according to the established inclusion criteria. The quality assessment was performed by the Newcastle-Ottawa Scale (NOS). The pooled odds ratio (OR) and 95% confidence intervals (CI) were calculated to estimate the association between the shift-work and rectal cancer risk. Based on heterogeneity significance, random-effect or fixed-effect model was used. Subgroup analyses were conducted to explore the night-shift and rotating-shift, respectively. Sensitivity analysis and publication bias detection were performed, and trim and fill analysis was also conducted. All statistical analyses were performed using RevMan software (version 5.3; Cochrane library) and STATA 15.0 statistical software (Stata Corp., College Station, TX), and all P values were two-tailed, the test level was 0.05. Results: Thirty-seven articles were obtained from database searching. Three articles involving 1,063 rectal cancer cases were included. All studies were considered moderate to high quality. All included studies investigated on the association between shift-work and rectal cancer risk. A statistically significant association between shift-work and increased rectal cancer risk was found (OR 1.53, 95%CI: 1.31, 1.79, P< 0.00001, I 2 = 35%). In subgroup analyses, night-shift work was associated with a non-statistically significant increased risk of rectal cancer (OR 1.25, 95%CI: 0.47, 3.32, P = 0.66, I 2 = 93%). In contrast, Rotating-shift was associated with a statistically significant increased rectal cancer risk (OR 1.35, 95%CI: 1.10, 1.65, P = 0.004, I 2 = 6%). Sensitivity analysis confirmed the stability of the result. Funnel plot, Egger's test (t = 1.69, P = 0.341), and Begg's test (z = 1.04, P = 0.296) found no publication bias of analysis. Trim and fill analysis on fixed-effect model showed the pooled OR kept stable after adding two “missing” studies (OR 1.403, 95%CI: 1.224, 1.609, P <0.05). Conclusions: The current meta-analysis demonstrates that shift-work is associated with increased rectal cancer risk. However, no association between night-shift work and rectal cancer risk was found. In contrast, association between rotating-shift work and increased rectal cancer risk was found. More original studies on this topic are needed to further explore shift-work impacts on rectal cancer risk.

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