Rotating night shift work, sleep and thyroid cancer risk in the Nurses’ Health Study 2

Abstract

Background and aim Thyroid cancer is the most common endocrine malignancy with rising incidence worldwide. We prospectively evaluated whether rotating night shift work and sleep disturbances are associated with incident thyroid cancer risk in the Nurses’ Health Study 2 (NHS2). Methods We assessed rotating night shift work (≥3 nights/month) history (cumulative number of years) at baseline and throughout follow-up (1989-2015) and sleep duration and sleep difficulty in 2001. Cox proportional hazard models, adjusted for potential confounders were used to calculate thyroid cancer hazard ratios (HR) and 95% confidence intervals (CI) for shift work history (0.1-4.9yrs, 5-9.9yrs, 10+yrs), sleep duration (≤5, 6, 7, 8, ≥9hours) and difficulty falling or staying asleep (little or none of the time, sometimes, most or all of the time). We further stratified the analyses of night shift work by sleep characteristics. Results We identified 588 incident cases among 114,534 women. We observed no association between night shift work history and thyroid cáncer risk (1-4.9 years: HR 1.19, 95% CI 0.98, 1.44; 5-9.9 years: HR 1.13 95% CI 0.86, 1.48; ≥10 years: HR 1.10, 95% CI 0.78, 1.54; Ptrend=0.55). Sleep difficulty was suggestively associated with higher incidence of thyroid cancer when reported sometimes (HR 1.26, 95% CI 0.95, 1.67) and most or all the time (HR 1.35, 95% CI 1.00, 1.81; Ptrend=0.03), compared to little or none of the time. Participants with >10 years of night shift work and ≤6 hours of sleep had a 2-fold increase in thyroid cancer risk (HR 2.23; 95%CI, 1.08-4.06). Shift workers with <5 years of shift work and frequent sleep difficulty had an increased risk of thyroid cancer (HR 1.95; 95% CI 1.03, 3.67). Conclusion We found evidence that rotating night workers with frequent sleep difficulty or short sleep had an increased risk of thyroid cáncer. Keywords night work, thyroid cancer