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The Dark Side of Light

Mar 11, 2013 08:38PM ● Published by Arden Haley

By Kathleen Jepsen
Photo Credit: NASA/GSFC
Edited by Sarah Hagerty

Blame Thomas Edison.
Although he didn’t invent the light bulb, he did improve upon it and patented a system for electricity distribution. In 1882, his Edison Illuminating Company provided electric current to 59 customers in lower Manhattan. Edison helped us light the candle, so we would no longer curse the darkness; but a growing body of evidence suggests that we may have reason to curse the brightness as well.

Nowadays, we live in perpetual daylight. Motivated by concerns about safety, crime, and a desire to extend our activities beyond the allotted cycle of the sun, we exist in almost total illumination—our roads, our shopping centers, our playing fields, our neighborhoods, all so brightly lit that they are visible from space. Edison would no doubt be astounded to see the latest NASA satellite photos that expose all our major cities, and most of the East coast, lit up like a Christmas tree.

Astronomers and naturalists have decried this situation for years, mourning the loss of our celestial experience—as sky glow from Light at Night (LAN) washes out our view of the Milky Way. But research shows that this proliferation of nighttime light may have far more serious consequences.

Melatonin, a hormone produced in the pineal gland at night, regulates the body’s biological clock, maintaining our circadian (daily function) rhythms. When the retina is subjected to light beyond the natural cycle of sunrise/sunset, melatonin production decreases. Scientists have linked this suppression to an epidemic of sleeplessness, depression, diabetes, obesity, and even cancer.

According to the Harvard Health Letter, their Medical School study that shifted the timing of human test subjects’ circadian rhythms found that blood sugar levels increased to a pre-diabetic state, and levels of leptin (a hormone that leaves us feeling full after a meal) decreased. A joint U.S.-Israeli study published in Proceeding of the National Academy of Sciences (PNAS) found that over the course of eight weeks, mice subjected to light beyond the normal spectrum gained up to 50 percent more weight compared to those within the normal exposure, even though both groups were given the same amount of food.

Other research results are more ominous. When melatonin is suppressed, it may spur the production of estrogen with unwelcome results. A Danish study in 2004 of 40,000 female nightshift workers, found that these women had an 85 percent higher risk of miscarriage and stillbirth compared to women who worked day shifts.

According to the Breast Cancer Fund, “high levels of melatonin at nighttime are important for regulation of both pituitary and ovarian hormones…enhancing the activity of pathways that can prevent the development of cancer.” Their 2008 report, “State of the Evidence: The Connection between Breast Cancer and the Environment,” cited laboratory tests in which melatonin inhibited the growth of mammary tumor cells in rats. Conversely, implanted tumors grew more aggressively when melatonin production was suppressed by light. A study published in the British Journal of Cancer in 2001 found that blind women had up to a 50 percent less risk of developing breast cancer because their retinas do not process light, leaving natural melatonin release unaltered.

According to the December 2008 issue of the Journal of Chronobiology, women living in neighborhoods where light was bright enough to read a book outside at midnight had a 73 percent higher risk of developing breast cancer than those residing in areas with the least outdoor artificial light. From 2006 to 2009, University of Connecticut epidemiologist Richard Stevens and colleagues at the University of Haifa conducted research that compared satellite measurements of light emissions to cancer rates in 164 countries. They found a direct correlation between an area’s use of nighttime lighting and rates of both breast cancer in women and prostate cancer in men.

Based on these and similar findings, the World Health Organization (WHO) declared in 2007 that the interruption of circadian rhythms inherent in nightshift work for women was “a probable carcinogen.” In 2012, the American Medical Association (AMA) issued a report, “Light Pollution: Adverse Effects of Nighttime Lighting,” a comprehensive look at previous scholarship. It raised alarms about the effects of both outside light (street light, commercial illumination) and inside light (late-night viewing of television, computers, bedroom brightness), with an increased concern about our exposure to blue light as a part of our nightly routines.

The average American gets six to eight hours of sleep each day. Many spend the hours beforehand bathed in the addictive splendor of blue-spectrum light, which emanates from LED (light-emitting diode) screens on computers, tablets, and electronic gadgets (as well as the newly mandated high-efficiency bulbs). Blue LEDs emit an intense, single wavelength that research has shown to be the biggest threat to melatonin release. A 2012 study by Rensselaer Polytechnic Institute found that a mere two-hour exposure to such light results in a melatonin suppression of 22 percent.

While no expert is advocating the abandonment of all outside illumination, or all inside technology, ample proof exists that we should adjust our routines to better accommodate the natural rhythms of our bodies. In order to ensure a brighter future, we might have to consider spending more time in the dark.

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