Indoor and outdoor artificial light-at-night (ALAN) and cancer risk: a systematic review and meta-analysis of multiple cancer sites and with a critical appraisal of exposure assessment

Abstract

Exposure to artificial light-at-night (ALAN) has been linked to cancer risk. Few meta-analyses on this topic have reviewed only breast cancer. This study aimed to systematically review and meta-analyze existing studies on ALAN exposure and cancer incidence, thoroughly evaluating exposure assessment quality. We considered observational studies (cohort, case-control, cross-sectional) on ALAN exposure (indoor and outdoor) and cancer incidence, measured by relative risk, hazard ratio, and odds ratio. We searched six databases, two registries, and Google Scholar from inception until April 17, 2024. Quality of studies was assessed using the Joanna Briggs Institute (JBI) critical appraisal tools. Random-effects meta-analysis was used to estimate relative risks (RR) and 95 % confidence intervals (CI) for ALAN exposures. We identified 9835 studies and included 28 for qualitative synthesis with 2,508,807 individuals (15 cohort, 13 case-control). Out of the included studies, 20 studies on breast cancer (731,493 individuals) and 2 studies on prostate cancer (53,254 individuals) were used for quantitative synthesis. Higher levels of outdoor ALAN were associated with breast cancer risk (meta-estimate = 1.12, 95 % CI 1.03-1.23 (I2 = 69 %)). We observed a non-significant positive association between indoor ALAN levels and breast cancer risk (meta-estimate = 1.07, 0.95-1.21, I2 = 60 %), and no differences by menopausal status. The meta-analysis for prostate cancer suggested a non-statistically significant increased risk for higher levels of outdoor ALAN (meta-estimate = 1.43, 0.75-2.72, I2 = 90 %). In the qualitative synthesis, we observed positive associations with non-Hodgkin lymphoma and colorectal, pancreatic and thyroid cancer. We found an association between outdoor ALAN and breast cancer risk. However, most studies relied on satellite-images with a very low resolution (1 to 5 km, from the Defense Meteorological Program [DMSP]) and without information on color of light. Future studies with better exposure assessment should focus on investigating other cancer sites.

AP-C was supported by the MINECO (Ministry of Economy in Spain) Grant no. PRE2019-089038, fellowship. AD was supported by an Alberta Innovates Summer Research Studentship and a Northern Alberta Clinical Trials and Research Centre Summer Studentship Award. KP has received funding from the EU Horizon Health (Grant 101080788). PL received funding from Synergy Respiratory & Cardiac Care, Sherwood Park, AB, Canada, and AstraZeneca Canada, and she reports personal fees from AstraZeneca Canada and GSK Canada, outside the submitted work. SM reports personal fees from Elsevier Inc. (USA), Synergy Respiratory & Cardiac Care (Canada), and Permanyer Inc. (Spain); lecture fees from Apollo Gleneagles Hospital (India) and Institute of Allergy, Kolkata (India), outside the submitted work. RM and HD received funding of the Asthma and Lung UK WAPG22/100005. HD additionally received funding by MRC-CSF-MR/V029460/1. AA and JFN are supported by the grant PID2020-117767GB-I00 of Spanish Ministry of Science and Innovation (MCIN/AEI/10.13039/501100011033); AA is supported by the Generalitat de Catalunya (2021SGR801). BH has received funding from the Instituto de Salud Carlos III (ISCIII) and the European Union NextGenerationEU/PRTR (Grant IHMC22/00017). ISGlobal acknowledges support from the Spanish Ministry of Science and Innovation through the "Centro de Excelencia Severo Ochoa 2019-2023" Program (CEX2018-000806-S), and support from the Generalitat de Catalunya through the CERCA Program.