Is there an association between artificial light-at-night (ALAN) exposure and cancer risk? A recent systematic review and meta-analysis published by Ahmedabad University's Assistant Professor at the Bagchi School of Public Health Subhabrata Moitra, suggests that higher levels of outdoor ALAN is associated with a 12% increased risk of breast cancer. Additionally, the study indicates a potential, though non-significant, increase in prostate cancer risk for outdoor ALAN.
Several studies have shown that the increasing amount of ALAN across the world results in wide-ranging light pollution that has negative health impacts on humans and ecosystems. It disrupts circadian rhythms and melatonin production, impacting sleep quality and increasing the likelihood of several diseases, particularly for hormone-dependent cancers. Professor Moitra's study is the synthesis of available evidence that focuses on ALAN exposure in relation to cancer risk and includes additional cancer types. This article is the second of the ALAN series, the previous study was published in BMC Medicine earlier this year where ALAN was found to be associated with an increased risk of allergic diseases such as allergic rhinitis, asthma, and skin allergies.
Professor Moitra's research looked at studies that show circadian disruption as an important mechanism affecting biological processes in the body. Circadian rhythms are natural cycles that control many bodily functions and can be adjusted daily by external signals, such as light, which acts as the main time-giver for the brain's internal clock.
This is further evidenced in the studies conducted on night shift workers, which found a moderate level of confidence in the connection between too much light at night, not enough daylight exposure, and disruptions in circadian rhythms, which could potentially lead to cancer. Night shift work has also been identified as a “probable carcinogen” by the International Agency for Research on Cancer However, Professor Moitra's study, which covers both indoor and outdoor settings and multiple cancer types, did not indicate any significant link between indoor ALAN exposure and breast cancer.
The research paper titled "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" published in the journal "Science of the Total Environment" highlights how most studies used low-resolution satellite images to assess outdoor ALAN without accounting for light colour, limiting exposure accuracy. It also highlights how most studies are restricted to breast cancer, calling for studies to broaden focus and explore the effects on other cancer types.