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. One group was exposed to long days of 16 hours of light and eight hours of darkness to simulate exposure to artificial light beyond the amount of natural light in a day; a second group was exposed to the same long day but were treated with melatonin; a third group was exposed to short days of eight hours of light and 16 dark hours. The fourth group received the same short days, but during the dark hours were exposed to a half-hour interval of light.
The results showed a clear link between LAN and cancer. Mice exposed to short days and uninterrupted dark hours had the smallest cancer growth (.85 cubic cm on average) while mice whose short days were interrupted with LAN had larger cancer growths (an average of 1.84 cubic cm ). As predicted, mice in the long days group fared worst with cancer growths averaging 5.92 cubic cm.
The study also showed melatonin suppression clearly influences tumor development. In mice whose group were expose to long days but treated with melatonin averaged tumor growth that mirrored mice in the short days group (.62 cubic cm) and had a death rate significantly lower than those in the non-treatment group.
The researchers say that their study showed that suppression of melatonin due to exposure to LAN is linked to the worrying rise in the number of cancer diagnoses over the past few years. However, it is not yet clear what mechanism causes this.
“Exposure to LAN disrupts our biological clock and affects the cyclical rhythm that has developed over hundreds of millions of evolutionary years that were devoid of LAN. 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 noted.
Lynette Summerill is an award-winning writer who lives in Scottsdale, Arizona. In addition to writing about cancer-related issues, she writes a blog, Nonsmoking Nation, which follows global tobacco news and events.