'Exposure to artificial light at night elevates cancer risk'

Haifa University researchers find higher risk of prostate cancer in men working night shifts.

By JUDY SIEGEL-ITZKOVICH
It isn’t only women who are at higher risk of cancer from working night shifts while being exposed to artificial light; now men have been found to face higher cancer risks as well.
In 2008, University of Haifa researchers found that being exposed to light at night instead of sleeping in darkness reduced melatonin production in the brain and raised the risk of breast cancer; now other scientists from the same university have found a higher risk of prostate cancer in men working night shifts. The study, by Dr. Rahel Ben-Shlomo of the university’s evolutionary and environmental biology department, has just been published in the journal Cancer Genetics and Cytogenetics.
The elevated risk is not due to working late at night per se, but stems rather from exposure to artificial light for long periods during these hours. The reduced melatonin hormone, the research team suggested, interferes with the division of cells, which is one of the mechanisms that are harmed in cancer.
Ben-Shlomo investigated the expression of genes in the cells of mice brains after the rodents were exposed to 12 hours of light and 12 hours of darkness. But during the dark period, artificial light was turned on for some of the mice for one hour while the control group remained in a darkened cage. Ben-Shlomo compared the gene expression in brain cells in the two groups.
Her previous work found that artificial light at night interferes with the proper functioning of the biological clock. Her new study discovered that cell division was harmed by the light at night and that a large number of genes in the mouse brains expressed themselves in an abnormal way when the animals were exposed to light at night. Ben-Shlomo explained that among the genes that behaved abnormally were those connected to the creation of malignant tumors, but also those genes that fight “cancer genes.” What was clear from the study, she said, was that “natural division of cells was harmed.”
The changes in gene expression resulted from only a one-time exposure to artificial light, said Ben-Shlomo. Now she will study what the effects are from many exposures.
Two years ago, University of Haifa biologist Prof. Avraham Haimm doctoral student Itai Kloog and Prof. Boris Portov published in Chronobiology International a study showing that exposure to light at night is the most powerful factor in breast cancer besides genetic defects. On the basis of their findings, they advised closing the shutters when going to bed, wearing eye shades if one is unable to darken the bedroom; avoiding night lights and lowering lights in working environments after sunset.
This team found that women who live in neighborhoods and streets withstrong outdoor lighting at night are more likely to contract breastcancer than those who have minimal nocturnal lighting. They suggestedthat melatonin is a powerful antioxidant that promotes the suppressionand minimizes the expression of cancer genes such as BRCA1 and BRCA2involved in some breast cancer and P53 involved in prostate cancer.
Soonbefore that research was published, a part of the World HealthOrganization announced that it had recognized night-shift work as a“probable carcinogen” and thus as risky as exposure to certain toxicsubstances. A previous study found that young children who had a lighton all night in their rooms were at higher risk for developingnearsightedness and that it may also slow their sexual development.


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