Rotating nightshift work and the risk of endometriosis in premenopausal women.

Abstract

The purpose of this prospective study was to study the association between rotating nightshift work and endometriosis risk within the Nurses' Health Study II. We found 89,400 women without diagnosed endometriosis at baseline; the 2062 laparoscopically confirmed cases that were documented during 16 years of follow-up evaluation formed our study population. Overall, there was no association between rotating nightshift work and risk of endometriosis. When the cases were categorized by infertility status, risk was elevated among women with concurrent infertility and ≥5 years of rotating nightshift work (rate ratio, 1.71; 95% confidence interval, 1.18-2.49; P(trend) = .005), compared with women with no rotating nightshift work. In contrast, there was no association among women without reported infertility (P(heterogeneity) = .003). Women who work rotating nightshifts for ≥5 years may have a modestly elevated risk of endometriosis if concurrently infertile. However, the relation between shiftwork, endometriosis, and infertility is complex, and the potential for bias because of a healthy or infertile worker effect must be considered.