Topline
States with an overexposure to artificial light pollution—particularly at night—are linked to an increased risk of Alzheimer’s disease, according to a new study by scientists at Rush University Medical Center, the latest research to suggest people’s likelihood of developing Alzheimer’s may be tied to their environments.
Key Facts
In the study published Friday by the Frontiers in Neuroscience journal, scientists say exposure to artificial outdoor light at night was correlated with a higher risk of developing Alzheimer’s disease—though the study didn’t make a direct causal link.
Researchers used satellite acquired data to determine nighttime light intensity in states and compared that data with Alzheimer’s disease prevalence in the same states, finding that a positive correlation was found in states with the most light pollution in every year studied (from 2012 to 2018).
States with the most light pollution—and the highest Alzheimer’s disease prevalence—included Florida, Connecticut and New Jersey, while Montana, New Mexico, Vermont, Idaho, Wyoming and Oregon had lower instances of both.
Nighttime light pollution had a stronger correlation to Alzheimer’s disease risk than alcohol abuse, chronic kidney disease, depression, heart failure and obesity, the study showed, but less of a link to the conditions of atrial fibrillation, diabetes, hyperlipidemia, hypertension and stroke.
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In people under age 65, however, nighttime light exposure was more strongly associated with Alzheimer’s prevalence than any of the other disease factors studied.
Light pollution is the latest in a list of environmental factors that studies suggest could be linked to the risk of developing Alzheimer’s disease, including living near green spaces, long-term exposure to air pollution and chemical exposures.
Big Number
80%. That’s how much of the global population experiences light pollution, according to the study.
Key Background
Light pollution, defined as nighttime artificial light from, for example, poorly shielded and overly bright light fixtures, has long been considered to be mostly harmless, researchers said, but more recent studies have linked light pollution to harsh ecological, behavioral, biological, and health consequences. The concept of light pollution was first pointed out by astronomers in the 1970s, according to the National History Museum, as those who studied the night sky noted the increasing impact of artificial light on their work. At the time, the sky was estimated to have been becoming brighter by between 3 and 6% every year, the museum said, but that rate has increased to almost 10% annually around the globe, with an even faster growth rate in North America (10.5%). In addition to impacting the view of the night sky—roughly 30% of people have lost the ability to see the Milky Way, according to the National Oceanic and Atmospheric Administration—scientists have noted that over illumination at night highlights the waste of energy contributing to climate change and can decrease the nighttime cleansing of the atmosphere. Other research, like the study published Friday, is also increasingly starting to suggest light pollution can have adverse effects on human and wildlife health. Light pollution, from LED lights and electronic devices in particular, impacts circadian sleep rhythms, according to the American Medical Association, which can increase the risk of obesity and decrease the production of melatonin. Exposure to artificial outdoor light at night is also associated with increased obesity, depression, anxiety, memory dysfunction, atherosclerosis and cancer, the Rush University Medical Center says.
Surprising Fact
Singapore, Qatar and Kuwait are among the most light polluted countries in the world, according to National Geographic.
Tangent
Sea turtles have long been studied as a species dramatically impacted by light pollution. Female sea turtles lay their eggs on beaches and their hatchlings navigate toward the sea by using the natural light of the moon to orient themselves away from land and toward the sea. When artificial light sources are introduced and mimic that natural light, however, newly hatched turtles become disoriented and can accidentally navigate away from the sea—a mistake most don’t survive. Similarly, about 10,000 migratory birds are hurt or killed each year by crashing into skyscrapers and high-rise buildings after being confused by brightly lit buildings, according to a study published in the National Library of Medicine.
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