I woke up at 2 this morning to the red glow of the Netflix end-of-movie screen again. To my own peril, it seems.
New research out of the University of Haifa shows a clear link between light at night and cancer in mice, with the suppression of melatonin playing a key role.
Earlier studies at Haifa demonstrate that, of people living in areas with higher nighttime illumination, men are more susceptible to prostate cancer and women to breast cancer than those who live in darker areas.
In this study, which involves many of the same researchers, the team wanted to test the hypothesis that light at night interferes with the body's natural production of melatonin, a hormone released during the dark hours of the 24-hour cycle and linked to the body's cycle of night-day activities.
Their conclusion: suppression of melatonin increases tumor development.
The researchers studied four groups of mice injected with cancerous cells: the first was exposed to 16 hours of light and 8 of darkness, the second to the same hours but with melatonin treatment, the third to 8 hours of light and 16 of darkness, and the fourth to the same but with half-hour intervals of light exposure at night.
The cancerous growths were smallest in mice exposed to short days (0.85 cubic cm. average), higher in mice exposed to intervals of light during dark hours (1.84 cubic cm. average), and highest in mice exposed to 16 hours of light without melatonin treatment (5.92 cubic cm. average). Meanwhile, tumor growth in mice exposed to 16 hours of light but treated with melatonin was 0.62 cubic cm. on average, or roughly the same as the size of the growth in mice exposed to the least amount of light.
"Exposure to LAN (light at night) disrupts our biological clock and affects the cyclical rhythm that has developed over hundreds of millions of evolutionary years that were devoid of LAN," the researchers note. "Light pollution as an environmental problem is gaining awareness around the world, and the World Health Organization...has already classified working the night shift as a higher grade of cancer risk."
More research is required to better understand whether quantity and type (as opposed to just duration) of light matters, and whether light exposure at night affects those who already have cancer differently than those who do not.