Animal study shows that exposure to light at night increase the risk of cancer due to suppression of Melatonin release

September 01, 2010

In a press release concerning new evidence of a connection between low melatonin and increased cancer risk by research scientists at the Center for Interdisciplinary Chronobiological Research of the University of Haifa in Israel it was stated that there was an association between light at night and an increased risk of cancer; and it is likely due to light-induced suppression of the hormone melatonin. Previously the same researchers found that men and women who reside in areas in which there is greater night-time exposure to artificial light have an increased risk of prostate and breast cancer. Suppression of melatonin, a hormone released by the pineal gland in response to darkness, was hypothesized to be the cause of the finding.

     In the current research, the team injected mice with cancerous cells and divided them into the following groups: exposure to 16 hours of light and 8 hours of darkness, or exposure to 16 hours of light and 8 hours of darkness plus melatonin, exposure to 8 hours of light and 16 hours of darkness, or the same regimen plus a one-half hour interval of light exposure during the 16 dark hours.

     At the end of the study, cancerous tumors in the mice that experienced 8 hours of light and 16 hours of uninterrupted darkness were on average far less than half the size of mice exposed to the half hour interval of light’s tumors. Tumors averaged 5.92 cubic centimeters among mice that were exposed to 16 hours of light, yet those treated with melatonin had tumors that averaged 0.62 cubic centimeters, as well as lower rates of mortality compared to untreated mice.

     “Light pollution as an environmental problem is gaining awareness around the world, and the World Health Organization’s International Agency for Research on Cancer (IARC) has already classified working the night shift as a higher grade of cancer risk,” the researchers note.