Chronotype differences in the risk of cancers, diabetes mellitus, and poor mental health among shift workers: a meta-analysis.

Night shift workers with morning chronotype had significantly elevated risk of breast cancer compared to daytime workers.

• Pooled odds ratio of 1.54 (95% CI 1.01–2.37) for breast cancer among morning chronotype night shift workers
• Analysis included 2247 breast cancer cases across included studies
• Fourteen studies were included in the overall review
• Six databases were searched from inception to September 2025

Night shift workers with evening chronotype had significantly elevated risk of breast cancer compared to daytime workers.

• Pooled odds ratio of 1.41 (95% CI 1.04–1.90) for breast cancer among evening chronotype night shift workers
• Analysis included 2247 breast cancer cases
• Both morning and evening chronotypes showed elevated breast cancer risk, suggesting chronotype-matched scheduling does not mitigate night shift risks for breast cancer

Night shift workers with evening chronotype were 84% more likely to develop prostate cancer than daytime workers.

• Analysis included 3045 prostate cancer cases across included studies
• The 84% elevated risk was specific to evening chronotype night shift workers
• Cohort and case-control study designs were included in this analysis

A positive dose-response relationship was identified between cumulative years of night shift work and prostate cancer risk among evening chronotype night shift workers.

• Each additional year of night shift work was associated with a 2.1% increase in prostate cancer risk among evening chronotype workers
• This dose-response relationship was statistically significant (P=0.012)
• This relationship was specific to evening chronotype workers and not reported for other chronotypes

Night shift workers with morning chronotype had significantly elevated risk of poor mental health compared to daytime workers.

• Pooled odds ratio of 1.19 (95% CI 1.12–1.27) for poor mental health among morning chronotype night shift workers
• Analysis included 2128 poor mental health cases across included studies
• Both morning and evening chronotype night shift workers showed elevated mental health risks

Night shift workers with evening chronotype had significantly elevated risk of poor mental health compared to daytime workers.

• Pooled odds ratio of 1.11 (95% CI 1.05–1.17) for poor mental health among evening chronotype night shift workers
• Analysis included 2128 poor mental health cases
• Evening chronotype showed a slightly lower pooled OR for poor mental health than morning chronotype (1.11 vs 1.19)

Chronotype-matched scheduling does not effectively mitigate the health risks associated with night shift work.

• Both morning and evening chronotypes showed elevated risks for breast cancer and poor mental health when working night shifts
• The study included cohort and case-control studies selected according to PRISMA guidelines
• Evening chronotype night shift workers were described as particularly susceptible to various chronic non-communicable diseases

The meta-analysis included studies covering breast cancer, prostate cancer, diabetes mellitus, and poor mental health outcomes in relation to shift work and chronotype.

• Fourteen studies were included in the final review
• The review comprised 2247 breast cancer cases, 3045 prostate cancer cases, 336,218 participants in diabetes studies, and 2128 poor mental health cases
• Studies were restricted to cohort and case-control designs
• Six databases were searched from inception through September 2025