Outdoor artificial light at night, non-Hodgkin lymphoma, and the California Teachers Study cohort

Abstract

Background: Circadian disruption has been implicated in a growing number of adverse health outcomes. Circadian disruptions due to outdoor artificial light at night (ALAN) have been associated with increased circulating levels of inflammation; a hallmark of cancer. We examined the association between outdoor ALAN and a cancer strongly associated with autoimmune and inflammatory conditions, non-Hodgkin lymphoma (NHL), in the prospective California Teachers Study (CTS) cohort. Methods: The CTS is a large prospective cohort of 133,477 women that were active or retired teachers and members of the California State Teachers Retirement System in 1995-96. Outdoor ALAN was assigned to participant addresses reported at study baseline through use of the New World Atlas of Artificial Night Sky Brightness. Among 105,937 women followed from 1995-2015, linkage to the California Cancer Registry identified 873 incident cases of NHL. Age-stratified Cox proportional hazards models were used to calculate hazard ratios (HR) and 95% confidence intervals (95% CI) for overall NHL and the most common NHL subtypes; diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL) and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). In multivariate analyses, we adjusted for subtype specific covariates (e.g. body mass index (BMI) for DLBCL). Results: Compared to residents in the lowest quintile, participants residing in the highest quintile of outdoor ALAN were more likely to develop NHL overall (HR 1.32, 95% CI 1.07-1.63), and, in particular, DLBCL (HR 1.87, 95% CI 1.16-3.02). The elevated risk for DLBCL remained statistically significant after adjusting for age, race/ethnicity, BMI, and socioeconomic status (DLBCL:HR 1.70, 95% CI 1.03-2.79, NHL:HR 1.32, 95% CI 1.06-1.65). There was no association between ALAN and FL or CLL/SLL. Conclusions: Increased DLBCL risk was observed among women residing in neighborhoods with higher levels of outdoor ALAN. Future research in circadian disruption and DLBCL may clarify potential biological processes implicated in this association.