Nightshift work and risk of breast and prostate cancer: a systematic review and meta-analysis, 2012-2023.

BACKGROUND

The International Agency for Research on Cancer classifies night shift work as Group 2A, a probable human carcinogen. This study updates the evidence on the association between night shift work and the risk of breast and prostate cancer.

METHODS

Searches were conducted in PubMed and Web of Science. Case-control and cohort studies were included if they assessed night work as a risk factor for breast or prostate cancer, had =100 participants, provided full text in English or Spanish, scored =6 on the Newcastle-Ottawa Scale, and reported relative risks or odds ratio with 95% confidence interval. Heterogeneity and study quality were evaluated. Data synthesis followed PRISMA guidelines.

RESULTS

Twenty-one studies including 586,890 participants were analysed. For breast cancer, significant association were found only in cohort studies, both overall (RR=0.82; 95%CI: 0.67-0.99; I2=91%) and for <10 years of night work (RR=0.75; 95% CI: 0.68-0.82; I2=0%). Average study quality was acceptable (score 7), although heterogeneity was substantial. For prostate cancer, case-control studies reported an OR of 1.14 (95%CI; 1.02-1.27; I2=25%). For exposures =10 years, both RR (2.20; 95%CI: 1.35-3.59) and OR (1.16; 95%CI: 1.03-1.30) were significant. Overall quality was moderate (score 6) with low heterogeneity (25%).

CONCLUSIONS

Weak associations between night shift work and prostate cancer are observed in case-control studies and among individuals with =10 years of exposure, but no consistent association was found for breast cancer. These findings remain inconclusive and highlight the need for further research.