The Possible Impact of Light at Night and Light Interference on Human Health

Corresponding author e-mail: ahaim@research.haifa.ac.il One of the most significant environmental changes that spread world wide in the twenty century is light at night (LAN). No doubt that LAN had a positive contribution to world economy, culture, health services transportation and sports. However it also exposed the human to abolishment of seasonality or to “seasons out of time”, while humans as other mammals show seasonality in several variables. The results of recent studies carried out in our center reviled that LAN and Light Interference (LI) have a significant impact on seasonal acclimatization in rodents as well as on human breast and prostate (BC and PC) cancers but not on lung and recto-colon cancers. The results of in vivo studies showed that inoculation of BC and PC mice cancer cells to mice and LAN, LI, and melatonin treatment had a significant effect on the proliferation of cancer cells, as assessed by tumor volume. The disruption of our circadian rhythms by LAN and light interference (LI) has impact also on daily rhythms of blood coagulation as we showed in short day (SD) acclimated rats exposed to LI. In such rats daily rhythms of prothrombin time (PT) while LI to SD-acclimated golden spiny mice Acomys russatus affected daily rhythms of immune variables. In regards to LAN and LI we should remember that light intensity, wave length and duration of exposure are important variables. The results of a recent study in our laboratory revealed that exposure of mice inoculated with PC cells to blue light at night (~470 nanometer) facilitated the proliferation of the PC cells relatively to mice exposed to long wave length illumination - red light (~700 nanometer). What is the mechanism? Results from our experiments show that LI is a stressor as assessed by the increase of stress hormones (adrenaline and cortisol). Furthermore, a melatonin treatment to mice inoculated with PC or BC cells had a negative effect on cell proliferation. In modern life children and pregnant mothers are exposed to LAN and LI, we are trying to understand if such exposure has an impact on health issues in adults. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil