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

Oct 22, 2024The Science of the total environment

Artificial Light at Night Indoors and Outdoors and Its Link to Risk of Various Cancers: A Review and Analysis of Exposure Methods

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Abstract

Higher levels of outdoor artificial light-at-night (ALAN) are associated with a 1.12 times increased risk of breast cancer.

A total of 28 observational studies involving 2,508,807 individuals were included in the review.
Among the included studies, 20 focused on breast cancer, encompassing 731,493 individuals.
A non-significant positive association was observed between indoor ALAN levels and breast cancer risk.
For prostate cancer, the analysis suggested a non-statistically significant increased risk associated with higher outdoor ALAN levels.
Qualitative findings indicated positive associations between ALAN exposure and non-Hodgkin lymphoma, as well as colorectal, pancreatic, and thyroid cancers.
Most studies used low-resolution satellite imagery for exposure assessment, which may limit the accuracy of findings.

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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 (I = 69 %)). We observed a non-significant positive association between indoor ALAN levels and breast cancer risk (meta-estimate = 1.07, 0.95-1.21, I = 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, I = 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. 2 2 2

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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

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