The findings of a study conducted by Professor Abraham Haim and colleagues at the Center for Interdisciplinary Chronobiological Research of the University of Haifa in Israel contributes to a growing body of research of an association between light at night and an increased risk of cancer caused by light-induced suppression of the hormone melatonin. Melatonin is a hormone that  our bodies release at night time  from the brain’s pineal gland, in response to darkness.


Dr. Haim has conducted other studies conducted at the University of Haifa that determined that women and men who live in areas where there is a higher exposure to artificial light at night experience an increased risk of  breast and prostate  cancer.  The findings suggest that its suppression, caused by the artificial light exposure is the cause.


They theorized that artificial light interrupts melatonin production and release  from the pineal gland during the dark part of the 24-hour cycle and which is linked to the body’s cyclical night-day activity and seasonality. When melatonin levels are low, the chance of developing cancer increases.


He noted, “High power light bulbs contribute more to ‘environmental light pollution’, which the study has shown is a carcinogenic pollution,” who also lead this study, published in the journal Sleep Science.


Dr. Haim and his colleagues during this current study set out to confirm or deny their theory. They injected mice were injected with malignant cancer and separated into four groups and received one of the following daily regimens: exposure to 16 hours of light and 8 hours of darkness, simulating artificial light exposure; a second group was exposed to the same cycle of light and darkness, and received melatonin; a third group was exposed to 8 hours of light and 16 hours of darkness; and a fourth group was exposed to  the same regimen plus a one-half hour interval of light exposure during the 16 dark hours.


At the study’s conclusion, the researchers found that the 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.