Night Shift Work and Risk of Breast Cancer in Women

Background: Night shift work involving circadian disruption has been associated with increased breast cancer rates in some epidemiological studies, but the evidence is still on debate.

Aim of the study: The objective of this study is to assess the association between night shift work and breast cancer in Mexican women.

Methods: A Case-control study was conducted with incident cases of breast cancer at the Instituto de Seguridad Social del Estado de México y Municipios. Cases were interviewed about past exposures prior to the final diagnosis. Controls were women without breast cancer matched on multiple sociodemographic characteristics.

Results: 101 cases and 101 matched controls were interviewed; this small sample size provided consistent, but wide estimates of the assessed associations. The multivariate conditional logistic regression showed that breast-feeding was associated with reduced risk for breast cancer (OR 0.12; 95% CI: 0.02-0.60); women who experienced early menarche (12 years) were more likely to develop breast cancer (OR 18.58; 95% CI 18: 2.19-148). Women who worked at night were more likely to develop breast cancer compared to women who never did (OR = 8.58; 95% CI: 2.19-33.8).

Conclusions: Our results are consistent with studies from other countries, which positively associated night shift work with breast cancer.