Night shift work and female breast cancer: a two-stage dose-response meta-analysis for the correct risk definition.
Level 3 - non-randomized controlled study
Meta-analysis of observational cohort and case-control studies
PubMed 39085800 · doi:10.1186/s12889-024-19518-2
What was done
Authors performed a two-stage dose-response meta-analysis to evaluate the relationship between night shift work exposure duration and female breast cancer risk. PubMed, EMBASE, and Cochrane Library were searched through December 30, 2022. Using eight inclusion criteria and evaluating study biases and confounder adjustments, 10 cohort studies (15,953 cases; 6,812,138 person-years) and 11 case-control studies (9,196 cases; 12,210 controls) were included, while two cohort and five case-control studies were excluded as unreliable. Risk estimates were pooled separately for cohort (risk ratios) and case-control (odds ratios) studies at 1, 10, 20, and 30 years of exposure.
What was found
In cohort studies, the pooled risk ratio (RR) for breast cancer at 1, 10, 20, and 30 years of night shift work was 1.0042 (95% CI 1.0014–1.0070), 1.0425 (95% CI 1.0138–1.0719), 1.0867 (95% CI 1.0278–1.1490), and 1.1328 (95% CI 1.0419–1.2317), respectively. In case-control studies, the pooled odds ratio (OR) at 1, 10, 20, and 30 years of exposure was 1.0213 (95% CI 1.0108–1.0319), 1.2346 (95% CI 1.1129–1.3695), 1.5242 (95% CI 1.2386–1.8756), and 1.8817 (95% CI 1.3784–2.5687), respectively.
Why it matters
This study quantitatively estimates the dose-dependent increase in female breast cancer risk associated with cumulative years of night shift work exposure.
Limits
The analysis relies entirely on observational studies, which cannot establish causality and remain susceptible to residual confounding. The risk estimates differed markedly between study designs (OR 1.88 vs RR 1.13 at 30 years), suggesting potential recall or selection bias in the retrospective case-control reports. Specific shift schedules, rotation frequency, and breast cancer subtypes were not reported in the abstract.
Cited by
- supports Shift work is associated with an increased risk of developing certain cancers, including breast cancer.