darker.
http://www.lef.org/whatshot/2010_09.htmMelatonin linked with cancer protection
The results of a study conducted by Professor Abraham Haim and colleagues at the Center for Interdisciplinary Chronobiological Research of the University of Haifa in Israel adds new evidence to an association between light at night and an increased risk of cancer due to light-induced suppression of the hormone melatonin.
Previous research conducted by Dr Haim 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.
For the current research, the team injected mice with cancerous cells and divided them to receive one of the following daily regimens: exposure to 16 hours of light and 8 hours of darkness, the same regimen 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 averaged 0.85 cubic centimeters in size, while those exposed to the half hour interval of light had tumors that averaged 1.84 cubic centimeters. 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.