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

Authors: Palomar-Cros A, Deprato A, Papantoniou K, Straif K, Lacy P, Maidstone R, Adan A, Haldar P, Moitra S, Navarro JF, Durrington H, Moitra S, Kogevinas M, Harding BN

Year: 2024

Category: Epidemiology

Journal: Science of The Total Environment

DOI: 10.1016/j.scitotenv.2024.177059

URL: https://www.sciencedirect.com/science/article/pii/S0048969724072164

Abstract

Overview

Exposure to artificial light-at-night (ALAN) has been linked to cancer risk. Previous meta-analyses have mainly focused on breast cancer, leaving other cancer sites underexplored. This systematic review and meta-analysis aimed to comprehensively evaluate existing studies on indoor and outdoor ALAN exposure and its relation to cancer incidence, with an in-depth assessment of exposure methodologies.

Methods

  • Types of studies: Observational (cohort, case-control, cross-sectional) on ALAN and cancer incidence
  • Exposure metrics: Relative risk, hazard ratio, and odds ratio
  • Search strategy: Six databases, two registries, and Google Scholar, encompassing publications up to April 17, 2024
  • Quality assessment tools: Joanna Briggs Institute (JBI) critical appraisal tools
  • Analysis: Random-effects meta-analysis for estimating pooled relative risks (RR) and 95% confidence intervals (CI)

Findings

  • Total studies reviewed: 9,835; included in qualitative synthesis: 28 studies (15 cohort, 13 case-control, 2,508,807 individuals)
  • Quantitative synthesis comprised 20 breast cancer studies (731,493 individuals) and 2 prostate cancer studies (53,254 individuals)
  • Key associations:
    • Higher levels of outdoor ALAN are associated with increased breast cancer risk (meta-estimate = 1.12, 95% CI 1.03–1.23, I2=69%)
    • Non-significant positive association found between indoor ALAN and breast cancer risk (meta-estimate = 1.07, 95% CI 0.95–1.21, I2=60%)
    • No difference in risk by menopausal status
    • For prostate cancer, a non-statistically significant increased risk associated with higher outdoor ALAN (meta-estimate = 1.43, 95% CI 0.75–2.72, I2=90%)
    • Qualitative review indicates positive links with non-Hodgkin lymphoma and colorectal, pancreatic, and thyroid cancers

Conclusion

The study establishes a connection between outdoor ALAN exposure and increased breast cancer risk, suggesting further possible links with other cancers. However, limitations in exposure assessment — primarily reliance on low-resolution satellite imagery and lack of light color data — call for improved methodologies in future research on ALAN-related cancer risks.

artificial light at night ALAN cancer risk breast cancer prostate cancer systematic review meta-analysis
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