Abstract
BACKGROUND: Nightshift work is a plausible risk factor for hematologic cancer, but epidemiological evidence remains sparse, especially for individual subtypes. We prospectively examined the association of rotating nightshift work with hematopoietic cancer risk. METHODS: This cohort study included US women from the Nurses' Health Study (NHS: n = 76 846, 1988-2012) and Nurses' Health Study II (NHSII: n = 113 087, 1989-2013). Rotating nightshift work duration was assessed at baseline (both cohorts) and cumulatively updated (NHSII). Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for overall hematopoietic cancer and specific histologic subtypes. All statistical tests were two-sided. RESULTS: We documented 1405 (NHS) and 505 (NHSII) incident hematopoietic cancer cases during follow-up. In NHS, compared with women who never worked rotating nightshifts, longer rotating nightshift work duration was associated with an increased risk of overall hematopoietic cancer (HR(1-14y) = 0.93, 95% CI = 0.83 to 1.04; HR(≥15y) = 1.28, 95% CI = 1.06 to 1.55; P (trend) = .009). In NHSII, results were similar though not statistically significant (HR(1-14y) = 0.99, 95% CI = 0.82 to 1.21; HR(≥15y) = 1.41, 95% CI = 0.88 to 2.26; P (trend) = .47). In the subtype analyses in the NHS, the association of history of rotating nightshift work with risk of diffuse large B-cell lymphoma varied by duration (HR(1-14y) = 0.71, 95% CI = 0.51 to 0.98; HR(≥15y) = 1.69, 95% CI = 1.07 to 2.67; P (trend) = .01) compared with those who never worked rotating nightshifts. Women reporting a longer history of rotating nightshifts also had suggestive (statistically nonsignificant) increased risks of overall non-Hodgkin lymphoma (HR(≥15y) = 1.19, 95% CI = 0.95 to 1.49), Hodgkin lymphoma (HR(≥15y) = 1.32, 95% CI = 0.43 to 4.06), and multiple myeloma (HR(≥15y) = 1.42, 95% CI = 0.85 to 2.39). CONCLUSIONS: Longer duration (≥15 years) of rotating nightshift work was associated with increased risks of overall and several subtypes of hematopoietic cancer.