Oct. 22, 2024 – This October, hundreds of thousands of Americans missed two of the world's most spectacular shows: the Northern lights and a rare comet. Even for those who were aware of them, light pollution made them difficult to see unless you went to a dark area and let your eyes adjust.
It doesn't get any easier – the night sky over North America has develop into about several times brighter 10% per year since 2011. More and more research is linking all this light pollution to a surprising range of health consequences: cancer, heart disease, diabetes, Alzheimer's diseaseand even low Sperm qualityalthough the explanations for these troubling associations aren't all the time clear.
“We have lost the contrast between light and dark and regularly confuse our physiology,” he said John HanifinPhD, aassociate Ddirector from Thomas Jefferson University's Light Research Program.
Our own galaxy is invisible to us almost 80% of people in North America. In 1994, an earthquake-triggered power outage in Los Angeles caused people to call Griffith Observatory and wonder about this blurry patch of sunshine within the night sky. It was the Milky Way.
Bright headlights, illuminated buildings, glowing billboards and street lamps fill our urban skies with a brightness that affects even rural dwellers. Since the invention of the sunshine bulb, we have now been ensuring our homes are vivid at night. Now devices that emit blue light – smartphones, television screens, tablets – have been linked to sleep problems.
But outside light can be necessary for our health. “Every photon counts,” Hanifin said.
Bright lights, big problems
On the one hand Study 2024 , Researchers used satellite data to measure light pollution at the house addresses of over 13,000 people. They found that those that lived in places with the brightest night skies had a 31% higher risk Hhypertension. Another study from Hong Kong showed a 29% higher risk of dying from coronary heart disease. And another person found one 17%higher risk of cerebrovascular diseases comparable to strokes or brain aneurysms.
Of course there may be air pollution in urban areas too, Noiseand a scarcity of greenery. In some studies, scientists controlled for these aspects, and the correlation remained strong (although air pollution from particulate matter did occur). be worse for Heart health as external light).
Research has found connections between glowing outside at night and other illnesses:
Breast cancer. “It’s a very strong connection,” he said Randy NelsonPhD, neuroscientist at West Virginia University. A study of over 100,000 teachers in California found that girls who lived in areas with the very best levels of sunshine pollution had one 12%higher risk. This effect is comparable to increasing the intake of highly processed foods by 10%.
Alzheimer's disease. In one study Outdoor light exposure at night was more strongly linked to the disease than even alcohol abuse or obesity, in line with a study published this fall.
diabetes. In one current studyPeople who lived in probably the most lit areas had a 28% higher risk of diabetes than those that lived in much darker places. In a rustic like China, scientists concluded that 9 million cases of diabetes could possibly be linked to light pollution.
What happens in your body when you're exposed to light at night?
Research has shown that night light (indoors and outdoors) is disruptive circadian Clocks, increases inflammation, affects cell division and suppresses melatonin, the “Hormon of Darkness.” “Darkness is very important,” Hanifin said. When he and his colleagues began studying the consequences of sunshine on human physiology many years ago, “people thought we were borderline crazy,” he said.
Nighttime lighting affects the health and behavior of Species as diverse as Siberian hamsters, zebra finches, mice, crickets and mosquitoes. Like most living things on earthHumans have internal clocks which might be synchronized to the 24-hour cycle of day and night. The master clock is in your hypothalamus, a diamond-shaped a part of the brain, but every cell Your body also has its own clock. Many physiological processes occur in line with circadian rhythms (a term derived from a Latin phrase meaning “about a day“), from the sleep-wake rhythm to hormone secretion, as well as processes involved in the progression of cancersuch as B. Cell division.
“There are special photoreceptors in the eye that do not handle visual information. They just send light information,” Nelson said. “If it gets light at the wrong time, you reset the clocks.”
This internal clock “prepares the body for various recurring challenges, such as eating,” it says Christian BenedictPhD, sleep researcher at Uppsala University, Sweden. “Light exposure [at night] This could mean, for example, that your insulin is being released at the wrong time, Benedict said, leading to “a jet lag-like state that then affects the ability to manage blood sugar.” Animal studies Confirm that nighttime light exposure is possible reduce glucose tolerance and alter insulin secretion – potential Pathways to diabetes.
The hormone melatonin, produced by the pineal gland in the brain during darkness, plays a key role in this modern battle. Melatonin helps you sleep, synchronizes the body's circadian rhythm, protects neurons from damage, regulates the immune systemAnd fights inflammation. But even a small beam of light at night can suppress its secretion. Less than 30 lux of light, about the level of a Pedestrian zone at nightmay Reduce melatonin by half.
When lab animals are exposed to nighttime light, they show “tremendous neuroinflammation” – inflammation of nerve tissue, Nelson said. In one experiment In humans, those who slept in dim light had higher levels of C-reactive protein in their blood. an inflammatory marker.
Low melatonin levels are also linked to cancer. It “allows the cancer cells’ metabolic machinery to become active,” Hanifin said. One of the consequences of melatonin is to stimulate natural killer cellswhat can Detect and destroy cancer cells. In addition, melatonin levels decrease. Estrogen may increasewhich could explain the connection between night light and breast cancer (estrogen). promotes tumor growth in breast cancer).
Researchers acknowledge that satellite data could also be too coarse to estimate how much light individuals are actually exposed to while sleeping. Plus, a lot of us stare at vivid screens. “But studies keep coming out,” Nelson said, suggesting that outdoor light pollution does have an effect.
When Researchers use light sensors worn on the wrist In over 80,000 Britons, they found that the more light the device registered between half past midnight and 6am, the greater the chance of its wearer developing diabetes several years later – no matter how long they really slept. According to the authors of the study, this supports the outcomes of satellite Data.
A similar study Researchers who used actigraphy with built-in light sensors and measured whether people slept in complete darkness for not less than five hours found that light pollution increased the chance of heart disease by 74%.
What are you able to do about it?
Not everyone's melatonin is affected by nighttime light to the identical extent. “Some people are very sensitive to very low light, while others are not as sensitive and require much, much more light stimulation [to impact melatonin]said Benedict. In a studySome volunteers needed 350 lux to reduce their melatonin levels by half. For people like that, turn on the light in the bathroom at night it wouldn't matter; For others, however, 6 lux was just as harmful – and that's true darker than twilight.
You can protect yourself by turning off the lights in your bedroom and packing away your screens, but avoiding light pollution outdoors can be more difficult. You can of course invest in high-quality blackout curtains, although some light can still penetrate inside. You can plant trees outside your windows, reorient any motion detector lights, and even start a petition Ask your local government to reduce over-lighting in buildings and make better decisions Street lights. You can support organizations like this International Dark Sky Associationwho work to preserve the darkness.
Lastly, you may want to change your habits. If you live in a particularly light-polluted area, such as District of ColumbiaAmerica's top spot for urban vibes, you might want to reconsider nighttime strolls or rides around the neighborhood. Instead, Hanifin says, read a book in bed with the lights “as dim as possible.” It was “a much better idea than being out in midtown Manhattan,” he said. According to current recommendations published According to Hanifin and his colleagues, the extent of illumination at eye level when sleeping must be not more than 1 lux – about that much That's what you'd get for those who had one Candle lit 1 meter away.
And if we are able to keep the outside dark and the celebrities appear again (including the stunning Milky Way), we may benefit from much more – a few of it Research suggests that stargazing can evoke positive emotions, a way of private growth, and “a variety of transcendent thoughts and experiences.”