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What is “light pollution?” Is it really a
factor in breast cancer?
The glow of city lights blotting out stars in the
night sky has frustrated many a stargazer, but recent studies have shown
that “light pollution” — defined as excess or obtrusive
light at night — can actually have serious health effects.
Researchers have found that exposure to bright nocturnal light can decrease
the human body’s production of melatonin, a hormone secreted at night
that regulates our sleep-wake cycles, and decreased melatonin production
has in turn been linked to higher rates of breast cancer in women.
“Light at night is now clearly a risk factor for
breast cancer,” says David Blask, a researcher at the Cooperstown,
N.Y.-based Mary Imogene Bassett Research Institute. “Breast tumors
are awake during the day, and melatonin puts them to sleep at night,”
he adds. Epidemiologist Richard Stevens of the U.S. Department
of Energy’s Pacific Northwest National Laboratory first discovered
the link between breast cancer and light pollution in the late 1980s.
Stevens found that breast-cancer rates were significantly higher in
industrialized countries, where nighttime lighting is prevalent, than in
developing regions. Lending credence to Stevens’ research are the
findings of another researcher, William Hrushesky of the South
Carolina-based Dorn Veterans Affairs Medical Center, who discovered that
female night-shift workers have a 50 percent greater risk of breast cancer
than do other working women. He also found that blind women have high
melatonin concentrations and unusually low rates of breast cancer. To reduce breast-cancer risks from light pollution, Prevention magazine
recommends nine hours of sleep nightly in a dark room devoid of both
interior (computer screens) and exterior (street lamps) light sources. A
study of 12,000 Finnish women found that those who slept nine hours nightly
had less than one-third the risk of a breast tumor than those who slept
only seven or eight hours. Even bright light from a trip to the bathroom
can have an effect, so dim nightlights are recommended for night lighting. Light pollution causes other problems besides
increased cancer risk. According to the Sierra Club, birds and animals can
be confused by artificial lighting, leading them away from familiar
foraging areas and disrupting their breeding cycles, and the photosynthetic
cycles of deciduous trees (those that shed their leaves in the fall) have
been shown to be disrupted by the preponderance of artificial nighttime
lights. Another environmental impact of excessive use of
artificial light is, of course, energy waste. The International Dark-Sky
Association computes that unnecessary nighttime lighting wastes more than
$1.5 billion in electricity costs around the world each year while
accounting for the release of more than 12 million tons of carbon dioxide,
the leading greenhouse gas, into the atmosphere. Individuals can do their
part by keeping lights dim or off at home at night — and persuading
their employers and local government offices to do the same.
For more information:
International Dark-Sky Association, www.darksky.org; Sierra Club,
newyork.sierraclub.org/longisland/lightpollution.html.
Send questions to Earth Talk, care of E/The Environmental Magazine,
P.O. Box 5098, Westport, CT 06881 or e-mail earthtalk@emagazine.com.
This article appears in May 31 – Jun 6, 2007.
