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

## TL;DR

This study finds that night shift workers with certain chronotypes are at higher risk for cancers, diabetes, and poor mental health.

## Contribution

The study is the first to meta-analyze the role of chronotype in the health risks of shift work.

## Key findings

- Night shift workers with morning or evening chronotypes have higher breast cancer risk.
- Evening chronotype night shift workers are 84% more likely to develop prostate cancer.
- There is a dose-response relationship between years of night shifts and prostate cancer risk for evening chronotype workers.

## Abstract

Shift work is associated with various leading causes
of premature death, which has been linked with
individuals with specific chronotypes. This study
synthesized evidence on chronotype’s role in associations
between ever shift work and health outcomes.

Six databases were searched (inception–September 2025)
for cohort/case-control studies assessing
chronotype-specific shift work impacts on breast/prostate
cancer, diabetes mellitus, and mental health. PRISMA
guidelines were used for reporting.

Fourteen studies were included in the review,
comprising 2247 breast cancer cases, 3045 prostate cancer
cases, 336 218 participants in diabetes studies, and 2128
poor mental health cases. Compared to daytime workers,
both night shift workers with morning or evening
chronotypes were more susceptible to breast cancer
[morning type: pooled odds ratio (OR) 1.54, 95%
confidence interval (CI) 1.01–2.37; evening type: pooled
OR 1.41, 95% CI 1.04–1.90) and poor mental health
(morning type: pooled OR 1.19, 95% CI 1.12–1.27; evening
type: pooled OR 1.11, 95% CI 1.05–1.17]. Notably, night
shift workers with evening chronotype were 84% more
likely to develop prostate cancer than daytime workers. A
positive dose–response relationship was identified
between cumulative years of night shifts and prostate
cancer among night shift workers with evening chronotype,
indicating a 2.1% increase in risk for each additional
year (P=0.012).

Chronotype-matched scheduling does not effectively
mitigate night shift risks. Nevertheless, evening
chronotype night shift workers are particularly
susceptible to various chronic non-communicable diseases,
with a notable positive dose–response relationship
observed between prostate cancer and evening chronotype
night shift workers.