Exposure to outdoor light at night could put people at a higher risk of developing Alzheimer’s disease (AD), according to a new study published in Frontiers in Neuroscience.
"We show that in the U.S., there is a positive association between AD prevalence and exposure to light at night, particularly in those under the age of 65," said first author Dr. Robin Voigt-Zuwala, an associate professor at Rush University Medical Center in Chicago, Illinois, in a press release.
"Nightly light pollution – a modifiable environmental factor – may be an important risk factor for AD."
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Some common sources of artificial light include street lamps, vehicles, illuminated signs, office buildings and other lighted structures.
In the study, researchers analyzed light pollution maps across the country, ranking each state’s "nighttime intensity data." They then looked at the corresponding levels of Alzheimer’s disease.
For people 65 and older, light pollution was a greater risk factor than obesity, depression, alcohol abuse and chronic kidney disease, the researchers found.
Other risk factors, however — such as high blood pressure, diabetes and stroke — outweighed the risk of light pollution for that age group.
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Those under 65 years old, however, appeared to be more sensitive to nighttime lighting exposure, which increased their Alzheimer’s risk more than any other risk factor.
"Certain genotypes, which influence early-onset AD, impact the response to biological stressors, which could account for increased vulnerability to the effects of nighttime light exposure," Voigt-Zuwala said in the release.
"Additionally, younger people are more likely to live in urban areas and have lifestyles that may increase exposure to light at night."
Previous studies have shown that light pollution is increasing by around 10% each year, causing the night sky to become brighter and reaching approximately 80% of the global population.
Light pollution has been shown to disrupt the circadian rhythm and reduce production of the hormone melatonin, which can lead to sleep problems.
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Insufficient sleep, in turn, is a proven risk factor for neurodegenerative diseases like Alzheimer’s.
One recent study published in the American Journal of Preventive Medicine found that getting only five hours of sleep per night can raise the risk of dementia by 30% for people 50 and older.
Among adults who have sleep-related movement disorders, the likelihood of dementia is nearly four times higher, the same study found.
Dr. Earnest Lee Murray, a board-certified neurologist at Jackson-Madison County General Hospital in Jackson, Tennessee, was not involved in the study, but spoke with Fox News Digital about the environmental factors that can affect the prevalence of dementias like Alzheimer's.
"We have known for some time that the lack of quality sleep has detrimental health effects, and this includes an increased risk of developing cognitive difficulties later in life," he said.
The brain relies on a circadian rhythm to restore itself during sleep, the doctor went on.
"Constant light exposure disrupts this circadian rhythm and limits the amount of time the brain is in the deeper, restorative stages of sleep," Murray said.
Based on the findings, the researchers recommend that people take steps to reduce their exposure to light pollution.
"Awareness of the association should empower people – particularly those with risk factors for AD – to make easy lifestyle changes," said Voigt-Zuwala.
"Easy-to-implement changes include using blackout curtains or sleeping with eye masks. This is useful especially for those living in areas with high light pollution."
Although the study only examined outdoor light exposure, the researchers also suggested making changes indoors, such as installing dimmers, using blue light filters and swapping to warm lightbulbs instead of cool.
Some have pushed for regulations to control outdoor lighting exposure.
"The legislation against light pollution is usually very weak and/or not well implemented," Fabio Falchi, Ph.D., a researcher at the Light Pollution Science and Technology Institute in Italy, told Fox News Digital.
"It is time to start putting limits on this pollutant, too, as with the rest of the other common pollutants."
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The study did have some limitations, the researchers acknowledged.
The data was gathered from a subset of the U.S. population, they stated, and individual outcomes may vary based on how long someone lived in an area with high light exposure.
"The study only looked at outdoor light pollution and did not include any type of data from indoor light pollution, such as from cell phones or televisions," Murray noted.
"However, it can clearly be implied that exposure to constant light from devices can lead to cognitive issues later in life, reinforcing the importance of limiting nocturnal light exposure from cell phones and other devices."
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The researchers called for more studies into the association between light pollution and Alzheimer’s.
Fox News Digital reached out to the study authors requesting comment.
