Night work and risk of endometriosis

Abstract

OBJECTIVE: To assess the relation between rotating night shift work and risk of laparoscopically confirmed endometriosis, which has recently been shown to increase risk in a case-control study.DESIGN: Prospective cohort study within the Nurses' Health Study II.MATERIALS AND METHODS: A total of 116,671 women, aged 26-46 years, were followed for up to 12 years (1989-2001). Total months nurses had worked on rotating night shifts for at least 3 nights per month was assessed in 1989, 1991, 1993, 1997, and 2001. Cox proportional hazards models (adjusted for age, age at menarche, parity, oral contraceptive use, body mass index, alcohol use, and smoking status) assessed the relation between night work and incidence of endometriosis.Table 1Relative risks of endometriosis by rotating night shift work.Case definitionAll womenNever InfertileConcurrent infertilityDuration of rotating night shift (years)CasesMV RR (95% CI)CasesMV RR (95% CI)CasesMV RR (95% CI)Never6071.004901.001131.001-4.99180.99 (0.89, 1.09)7200.97 (0.87, 1.09)1861.02 (0.80, 1.29)5-9.92371.07 (0.92, 1.24)1760.99 (0.83, 1.18)581.34 (0.97, 1.85)≥10870.94 (0.75, 1.18)710.89 (0.69, 1.15)161.31 (0.77, 2.23)p for trend0.810.540.06Note: RR=rate ratio; MV=multivariable; CI=confidence interval. Open table in a new tab CONCLUSIONS: In this large, prospective assessment, we did not find evidence of an association between rotating night shift work and risk of laparoscopically confirmed endometriosis in all cases, however there was the suggestion of increased risk among infertile cases. More detailed analyses to address light at night exposure are ongoing. OBJECTIVE: To assess the relation between rotating night shift work and risk of laparoscopically confirmed endometriosis, which has recently been shown to increase risk in a case-control study. DESIGN: Prospective cohort study within the Nurses' Health Study II. MATERIALS AND METHODS: A total of 116,671 women, aged 26-46 years, were followed for up to 12 years (1989-2001). Total months nurses had worked on rotating night shifts for at least 3 nights per month was assessed in 1989, 1991, 1993, 1997, and 2001. Cox proportional hazards models (adjusted for age, age at menarche, parity, oral contraceptive use, body mass index, alcohol use, and smoking status) assessed the relation between night work and incidence of endometriosis. Note: RR=rate ratio; MV=multivariable; CI=confidence interval. CONCLUSIONS: In this large, prospective assessment, we did not find evidence of an association between rotating night shift work and risk of laparoscopically confirmed endometriosis in all cases, however there was the suggestion of increased risk among infertile cases. More detailed analyses to address light at night exposure are ongoing.