Night shift work and risk of colorectal cancer: a prospective cohort study among 56 477 female nurses in the Netherlands

Linske de Bruijn; Nina E Berentzen; Roel C H Vermeulen; Jelle J Vlaanderen; Hans Kromhout; Katarzyna Jóźwiak; Monique E van Leerdam; Flora E van Leeuwen; Michael Schaapveld

doi:10.1136/oemed-2024-109878

Night shift work and risk of colorectal cancer: a prospective cohort study among 56 477 female nurses in the Netherlands

Linske de Bruijn
, Nina E Berentzen
, Roel C H Vermeulen
, Jelle J Vlaanderen
, Hans Kromhout
, Katarzyna Jóźwiak
, Monique E van Leerdam
, Flora E van Leeuwen
, Michael Schaapveld^*

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

Objectives Night shift work has been classified as probably carcinogenic to humans, possibly related to suppression of melatonin secretion. Although experimental studies suggest that melatonin inhibits intestinal tumor proliferation, epidemiological evidence for a relationship between night shift work and colorectal cancer (CRC) risk is lacking.

Methods We prospectively examined the association between night shift work and CRC in the Nightingale Study. We included 56 477 Dutch female nurses who completed a questionnaire in 2011, including occupational history with detailed (historical) information on night shift work. Until February 2025, 468 incident CRCs were recorded. Age-adjusted HRs and 95% CIs for associations between night shift work variables and CRC risk were estimated using Cox regressions.

Results CRC risk did not differ between nurses who ever or never worked night shifts (HR=1.13; 95% CI=0.89 to 1.44). A longer duration of working night shifts (≥20 years: HR=1.19; 95%CI=0.89 to 1.60) was neither associated with CRC risk. However, a higher average number of consecutive night shifts per month (continuous per shift; HR=1.04, 95%CI=1.00 to 1.07) and a higher cumulative number of performed night shifts (continuous per 250 shifts: HR=1.02; 95%CI=1.00 to 1.04) were associated with a slightly increased risk. Chronotype did not affect the associations of CRC risk with night shift work.

Conclusions Although a longer duration of night shift work was not associated with CRC risk, both a higher frequency of and a higher cumulative exposure to night shifts were associated with slightly higher risk, suggesting a potential association between extensive exposure to night shift work and CRC risk.

Original language	English
Pages (from-to)	396-402
Number of pages	7
Journal	Occupational and Environmental Medicine
Volume	82
Issue number	8
Early online date	10 Sept 2025
DOIs	https://doi.org/10.1136/oemed-2024-109878
Publication status	Published - 17 Oct 2025

Bibliographical note

Publisher Copyright:
© Author(s) (or their employer(s)) 2025. No commercial re-use. See rights and permissions. Published by BMJ Group.

Funding

The Nightingale study is financially supported by the ZonMw Programme Electromagnetic Fields and Health (ZonMw, grant numbers 8520001 and 85500003). This study was supported by the Dutch Cancer Society (KWF Kankerbestrijding, grant numbers 6987 and 12560) and by an institutional grant of the Dutch Cancer Society and of the Dutch Ministry of Health, Welfare and Sport (Ministerie van Volksgezondheid, Welzijn en Sport). The funders did not play any part in designing the study protocol, data analyses, data interpretation or manuscript preparation.

Funders	Funder number
Ministerie van Volksgezondheid, Welzijn en Sport
ZonMw Programme Electromagnetic Fields and Health
ZonMw	8520001, 85500003
KWF Kankerbestrijding	12560, 6987

Keywords

Circadian Rhythm
Medical Oncology
Occupational Health
Shift Work Schedule

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1136/oemed-2024-109878

Cite this

de Bruijn, L., Berentzen, N. E., Vermeulen, R. C. H., Vlaanderen, J. J., Kromhout, H., Jóźwiak, K., van Leerdam, M. E., van Leeuwen, F. E., & Schaapveld, M. (2025). Night shift work and risk of colorectal cancer: a prospective cohort study among 56 477 female nurses in the Netherlands. Occupational and Environmental Medicine, 82(8), 396-402. https://doi.org/10.1136/oemed-2024-109878

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title = "Night shift work and risk of colorectal cancer: a prospective cohort study among 56 477 female nurses in the Netherlands",

abstract = "Objectives Night shift work has been classified as probably carcinogenic to humans, possibly related to suppression of melatonin secretion. Although experimental studies suggest that melatonin inhibits intestinal tumor proliferation, epidemiological evidence for a relationship between night shift work and colorectal cancer (CRC) risk is lacking. Methods We prospectively examined the association between night shift work and CRC in the Nightingale Study. We included 56 477 Dutch female nurses who completed a questionnaire in 2011, including occupational history with detailed (historical) information on night shift work. Until February 2025, 468 incident CRCs were recorded. Age-adjusted HRs and 95\% CIs for associations between night shift work variables and CRC risk were estimated using Cox regressions. Results CRC risk did not differ between nurses who ever or never worked night shifts (HR=1.13; 95\% CI=0.89 to 1.44). A longer duration of working night shifts (≥20 years: HR=1.19; 95\%CI=0.89 to 1.60) was neither associated with CRC risk. However, a higher average number of consecutive night shifts per month (continuous per shift; HR=1.04, 95\%CI=1.00 to 1.07) and a higher cumulative number of performed night shifts (continuous per 250 shifts: HR=1.02; 95\%CI=1.00 to 1.04) were associated with a slightly increased risk. Chronotype did not affect the associations of CRC risk with night shift work. Conclusions Although a longer duration of night shift work was not associated with CRC risk, both a higher frequency of and a higher cumulative exposure to night shifts were associated with slightly higher risk, suggesting a potential association between extensive exposure to night shift work and CRC risk.",

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note = "Publisher Copyright: {\textcopyright} Author(s) (or their employer(s)) 2025. No commercial re-use. See rights and permissions. Published by BMJ Group.",

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de Bruijn, L, Berentzen, NE, Vermeulen, RCH , Vlaanderen, JJ , Kromhout, H, Jóźwiak, K, van Leerdam, ME, van Leeuwen, FE & Schaapveld, M 2025, 'Night shift work and risk of colorectal cancer: a prospective cohort study among 56 477 female nurses in the Netherlands', Occupational and Environmental Medicine, vol. 82, no. 8, pp. 396-402. https://doi.org/10.1136/oemed-2024-109878

TY - JOUR

T1 - Night shift work and risk of colorectal cancer

T2 - a prospective cohort study among 56 477 female nurses in the Netherlands

AU - de Bruijn, Linske

AU - Berentzen, Nina E

AU - Vermeulen, Roel C H

AU - Vlaanderen, Jelle J

AU - Kromhout, Hans

AU - Jóźwiak, Katarzyna

AU - van Leerdam, Monique E

AU - van Leeuwen, Flora E

AU - Schaapveld, Michael

PY - 2025/10/17

Y1 - 2025/10/17

N2 - Objectives Night shift work has been classified as probably carcinogenic to humans, possibly related to suppression of melatonin secretion. Although experimental studies suggest that melatonin inhibits intestinal tumor proliferation, epidemiological evidence for a relationship between night shift work and colorectal cancer (CRC) risk is lacking. Methods We prospectively examined the association between night shift work and CRC in the Nightingale Study. We included 56 477 Dutch female nurses who completed a questionnaire in 2011, including occupational history with detailed (historical) information on night shift work. Until February 2025, 468 incident CRCs were recorded. Age-adjusted HRs and 95% CIs for associations between night shift work variables and CRC risk were estimated using Cox regressions. Results CRC risk did not differ between nurses who ever or never worked night shifts (HR=1.13; 95% CI=0.89 to 1.44). A longer duration of working night shifts (≥20 years: HR=1.19; 95%CI=0.89 to 1.60) was neither associated with CRC risk. However, a higher average number of consecutive night shifts per month (continuous per shift; HR=1.04, 95%CI=1.00 to 1.07) and a higher cumulative number of performed night shifts (continuous per 250 shifts: HR=1.02; 95%CI=1.00 to 1.04) were associated with a slightly increased risk. Chronotype did not affect the associations of CRC risk with night shift work. Conclusions Although a longer duration of night shift work was not associated with CRC risk, both a higher frequency of and a higher cumulative exposure to night shifts were associated with slightly higher risk, suggesting a potential association between extensive exposure to night shift work and CRC risk.

AB - Objectives Night shift work has been classified as probably carcinogenic to humans, possibly related to suppression of melatonin secretion. Although experimental studies suggest that melatonin inhibits intestinal tumor proliferation, epidemiological evidence for a relationship between night shift work and colorectal cancer (CRC) risk is lacking. Methods We prospectively examined the association between night shift work and CRC in the Nightingale Study. We included 56 477 Dutch female nurses who completed a questionnaire in 2011, including occupational history with detailed (historical) information on night shift work. Until February 2025, 468 incident CRCs were recorded. Age-adjusted HRs and 95% CIs for associations between night shift work variables and CRC risk were estimated using Cox regressions. Results CRC risk did not differ between nurses who ever or never worked night shifts (HR=1.13; 95% CI=0.89 to 1.44). A longer duration of working night shifts (≥20 years: HR=1.19; 95%CI=0.89 to 1.60) was neither associated with CRC risk. However, a higher average number of consecutive night shifts per month (continuous per shift; HR=1.04, 95%CI=1.00 to 1.07) and a higher cumulative number of performed night shifts (continuous per 250 shifts: HR=1.02; 95%CI=1.00 to 1.04) were associated with a slightly increased risk. Chronotype did not affect the associations of CRC risk with night shift work. Conclusions Although a longer duration of night shift work was not associated with CRC risk, both a higher frequency of and a higher cumulative exposure to night shifts were associated with slightly higher risk, suggesting a potential association between extensive exposure to night shift work and CRC risk.

KW - Circadian Rhythm

KW - Medical Oncology

KW - Occupational Health

KW - Shift Work Schedule

UR - https://www.scopus.com/pages/publications/105015647261

U2 - 10.1136/oemed-2024-109878

DO - 10.1136/oemed-2024-109878

M3 - Article

SN - 1351-0711

VL - 82

SP - 396

EP - 402

JO - Occupational and Environmental Medicine

JF - Occupational and Environmental Medicine

IS - 8

ER -

Night shift work and risk of colorectal cancer: a prospective cohort study among 56 477 female nurses in the Netherlands

Abstract

Bibliographical note

Funding

Keywords

UN SDGs

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