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Goodnight Moon: Study Finds More Evidence Lights at Night Linked to Cancer

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Cancer related image Photo: Getty Images

High-powered light bulbs may be producing more than light pollution. It may be contributing to an disturbing increase in breast cancer among women and prostate cancer in men.

A new study from the Center for Interdisciplinary Chronobiological Research at the University of Haifa in Israel has found an additional link between "Light At Night" (LAN) and cancer. The research adds to a growing body of evidence that exposure to too much light at night can raise the risk of cancer by interfering with the brain’s production of a tumor-suppressing hormone.

Earlier studies have shown that people living in neighborhoods brightly-lit at night are more susceptible to prostate and breast cancer. Scientists have known for years that rats raised in cages where the lights are left on for much of the night have higher cancer rates than those allowed to sleep in the dark. And epidemiological studies add further credence, showing nurses, flight attendants and other women who typically work the night shift have breast cancer rates 60 percent above normal, even when other factors such as diet differences are factored in.

Professor Abraham Haim, who led the new study, set out to establish or refute the claim of previous studies showing LAN harms melatonin production. Melatonin is a hormone released from the brain’s pineal gland primarily at night as part of the body’s cyclical night-day activity. The hormone helps prevent tumor formation. However, melatonin levels drop precipitously in light.

For instance, previous studies have shown that when those rats kept in LAN cages were injected with melatonin, their cancer rates went to nearly normal, and blind women, whose eyes can’t detect light have superior melatonin production and lower-than-average breast cancer rates.

In the current study, Professor Haim and his team tested the melatonin hypothesis by injecting four groups of mice with cancer cells.

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