When going for a checkup, patients might do a double take when doctors ask them a new question in addition to how much they smoke, drink, or exercise. That question is, “Are you getting the right kind of light?” This isn’t a visit to a practitioner in hippy Haight-Ashbury or New Agey Sedona. This exchange happens in forward-thinking medical offices right now.
Today, a range of illnesses is brought about by the lack of exercise, poor diet, insufficient sleep, widespread pollution, and bad genes. But another culprit exists—the light bulb. Research shows that animals exposed to artificial light succumb to a range of ailments, including an “increase in cancer, cardiovascular disease, diabetes, and obesity,” said professor Mariana Figueiro, director of the Lighting Research Center at Rensselaer Polytechnic Institute (RPI). Animals are not alone. Experts have uncovered that shift workers—those performing the millions of jobs, from security guards to surgeons, at times other than nine to five—have an increase in the risk of cancer and heart disease. By culling reams of data about maladies and connecting them to where people live, what they do, and who they are, researchers have found an epidemiological smoking gun. Ruling out all the other medical factors, one cause for these afflictions is the bright lights beaming over their heads. The lights disrupt their body clock, or circadian rhythm, bringing about these health issues.
Specifically, we are experiencing too much of the wrong kind of light at the wrong part of the day, and these lights affect our health.
In 2002, our understanding of the function of the eye radically changed with a discovery by David Berson. He found there is a special light detector, a unique photoreceptor, in the eye (the retina) that doesn’t contribute to vision. This part of the eye acts like Paul Revere. Instead of translating the message “one if by land, two if by sea,” this photoreceptor informs the body if it is day or night. Just as Paul Revere warned the patriots in the American Revolution to prepare for ground or naval warfare, this part of the eye alerts the body to prepare for day or night.
We are experiencing too much of the wrong kind of light at the wrong part of the day, and these lights affect our health.
When this sensor detects light—being most sensitive to sky blue light—a message cascades from the eye to the brain to the rest of the body to let it know it is daytime. Specifically, that message zips down the optic nerve in the back of the eye to the part of the brain’s hypothalamus called the suprachiasmatic nucleus (or SCN). The SCN telegraphs a message to a small, pea-sized part of the brain, the pineal gland, to stop secreting melatonin, a chemical that alerts the body that it is nighttime. The throttling off of melatonin completes the chemical Paul Revere message that “morning is coming, morning is coming.”
Melatonin is an ancient molecule secreted exclusively at night that communicates to cells in our bodies that it is evening. “It is an old chemical that evolved with us,” said Thomas Wehr, scientist emeritus at the National Institute of Mental Health. The body needs such a signal because essentially humans are two different organisms—a daytime one and a nighttime one. As a way to conserve energy, our bodies have a time of being “on” and “off.” The state we are in is switched on by the lights around us, with melatonin signaling the mode. During the day, our temperature, metabolism, and the amount of growth hormone in the body increases. In the evening, they all decrease and we log off. With artificial lights, however, our bodies don’t enter this necessary rest mode. The affects are already perceivable: “Modern humans are taller than their ancestors,” said Thomas Wehr. “It is partly related to nutrition and other factors, but it is also related to artificial light.”
Before electric lights, human physiology was connected to the seasons. More women got pregnant in the late spring and summer. Our bodies tracked the time of year by following the changing length of the amount of daylight between dusk and dawn. With the longer days of the summer, we produced less melatonin than in the winter, and with less melatonin, there was more growth hormone and more opportunity for growth. Today, however, artificial lights nearly blind our bodies from the time of year. “We’ve almost wiped out our seasonal variation in conception rates,” said Wehr.
Poets say that the eye is the window to the soul. Scientists would say that the eye is a clock.
For humans, being under Edison’s electric lights puts us in a perpetual summertime mode with nearly double the growth hormone in our systems than we have on a winter evening. In this constant growth mode, the whole body swims in growth hormone. Every cell is exposed and will respond to this overstimulation. “If you are continuously bombarded with these summer-level growth hormones, with that is a risk of cancer,” said Wehr.
Nobel Laureate Aziz Sancar found that the “circadian system affects the processes that we know are involved in the causes of cancer,” said Richard Stevens, a cancer epidemiologist at the University of Connecticut. There is a “circadian connection to how our cells will repair the damage to our DNA.” The details of what is happening are incomplete, but this work underscores that our bodies have a growth mode and a repair mode, and we need the healing that comes with the dark.
When it comes to women’s health, artificial light is one factor that is often overlooked for breast cancer. According to Stevens, “it has been suggested that the pandemic of breast cancer could be explained by the use of electric lights.” More studies are needed to understand what is going on, but one population tells scientists they may be heading in the right direction. “Blind women are at a lower risk for breast cancer,” said Stevens. “They cannot perceive light at night.” Their physiology isn’t swayed by the lights. Many medical reports show that blind women are outliers for breast cancer, but much more work is needed to understand how the glow of artificial lights affects women.
A day elapses in 24 hours; our internal clock averages 24.2. If we were placed in a dark cave with no visual cues, we would slip behind the solar day, like slow, antique timepieces.
Poets say that the eye is the window to the soul. Scientists would say that the eye is a clock, or rather, like the reset button on a clock. Our bodies contain an intrinsic, built-in rhythm where we anticipate the onset of the day, but our body clocks lag by about twelve minutes. A day elapses in 24 hours; our internal clock averages 24.2. If we were placed in a dark cave with no visual cues, we would slip behind the solar day, like slow, antique timepieces. When we see light in the morning, however, specifically its sky blue light, our biological clocks synchronize with Earth again. The sensitivity of the Paul Revere photoreceptor to the color of sky blue is a clever choice by nature and makes sense biologically.
The best way to inform the body that it is daytime is to specially tune part of the eye to this iconic color, just like tuning to a specific radio station. Mother Nature could have used all of white light, which is made up of a rainbow of colors (red, orange, yellow, green, blue, indigo, and violet). A lightning storm, with white electric bolts, however, could have accidentally drawn our ancestors from nighttime mode to daytime mode. Sky blue exists unequivocally in the day; it is a unique signal to tell the body that it is time to switch. Unfortunately, artificial lights do not fully emulate the light from nature, from the sun. The mighty sun contains all the colors of the rainbow in its light. Artificial lights contain only part of the spectrum; incandescent bulbs are redder, compact fluorescent bulbs are bluer. So how can modern citizens live well under the glow of artificial lights and correct the course charted by Edison? The prescription is simple.
We must not look at light bulbs as innocuous objects glowing in the background, but as prime movers of human health.
According to cancer epidemiologist Richard Stevens, we need “dim evenings and bright mornings.” The day must start with body clock-resetting bright blue light in the morning. “Taking a walk is the best thing. You get exercise and you get a bolus of the bright blue light,” said Stevens. For those who are indoors, LED lights and bright compact fluorescent bulbs are pretty strong in the blue range of light, too. Having lots of blue light during the course of the day is good. But the type of light must change as the day progresses. We need redder light in the evening. This includes reducing the blue light from our computer monitors, television displays, and cellphone screens. “Starting at dusk, dim [the lights] way down, and have a light source that is incandescent,” said Stevens.
To improve human health, people need to get the right type of light at the right time of day. This is not a mystical claim, but a medical certitude. “Light is the driver of your biological clock,” said Figueiro. “It drives everything in your body.” And for that we must not look at light bulbs as innocuous objects glowing in the background, but as prime movers of human health.
Excerpted from The Alchemy of Us: How Humans and Matter Transformed One Another by Ainissa Ramirez. Published by The MIT Press. Copyright © 2020 by Ainissa Ramirez. All rights reserved.