Light at night, melatonin and breast cancer

摘要

A recent paper published in Chronobiology International hypothesized that exposure to light at night (LAN) is coincident with decreased melatonin secretion, epigenetic modifications and results in a higher breast cancer tumor growth rate (Schwimmer et al., 2013). The study involved the inoculation of Balb/ c mice with 4T1 mouse breast cancer cells and their followup over the subsequent 21 days. Three groups of mice were studied: (1) mice maintained on a 8L:16D photoperiod, (2) mice subjected to 30 minutes of light, starting 7 h after the onset of darkness (LAN; presumably commencing the day of inoculation) and (3) mice exposed to the LAN, but given melatonin in their drinking water. The primary outcomes of the experiment were that mice subjected to LAN had the greatest tumor burden while those mice subjected to LAN and given melatonin had the lowest tumor burden. In addition, LAN decreased global DNA methylation in the tumors compared to the control group, while treatment with melatonin partially reversed this effect.