Light at Night May Increase Risk of Cancer


A new study published in the journal Sleep Science reached similar conclusions to previous studies that there is a link between light at night (LAN) and cancer. Previous studies by the researchers at the Center for Interdisciplinary Chronobiological Research at the University of Haifa showed that people who lived in areas with more night time illumination were more at risk for prostate cancer in men and breast cancer in women. In this follow up study they hypothesised that LAN harms the production of melatonin, a hormone released from the pineal gland during the dark and linked to the body’s cyclical night-day activities and seasonality and when this hormone is suppressed there is a rise in cancer cases.

To establish or refute this hypothesis the researchers studies 4 groups of lab mice that were injected with cancerous cells and subjected to one of the following: 1) long days of 16 hours of light and 6 hours of darkness; 2) same long days but were treated with melatonin; 3) short days of 8 hours light and 16 hours of darkness; and 4) short day but during the dark hours was exposed to a half hour interval of light.

Results showed those exposed to short days had the smallest cancerous growths (average 0.85 cubic centimeters) while those exposed to the interval LAN during dark hours had larger growths (average 1.84 cubic centimeter) and those exposed to long days had even larger growths (average of 5.92 cubic centimeters). Results also showed that suppression of melatonin had an effect on tumor development. Tumors in the mice exposed to long days but treated with melatonin were smaller (average 0.62 cubic centimeter) which was similar to the size of the tumors in those exposed to short days. The death rate of mice treated with melatonin was also lower than those who did not receive it. Thus, they concluded that their results show a link between LAN and cancer and the suppression of melatonin and cancer growth.

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