A Top Risk Factor for Alzheimer's May Surprise You

Key Takeaways

• A new study found a link between outdoor light pollution and the prevalence of Alzheimer's disease.
• For adults younger than 65, excessive light pollution increased the risk of Alzheimer's more strongly than issues like heart disease.
• Light pollution may contribute to Alzheimer's risk by disturbing circadian rhythms and interfering with good sleep.

In our modern world, the increasing use of bright outdoor artificial light has led to greater productivity, safety, and convenience, but overexposure can disrupt our circadian rhythms and sleep, which can in turn have a negative effect on our physical and mental health.

New research published this week in Frontiers in Neuroscience has found that excessive artificial light at night, or "light pollution," may contribute to more people developing Alzheimer's disease , especially adults younger than 65.

"Other studies show that light pollution is associated with numerous disorders and diseases, such as sleep problems, obesity, and even cancer," says the lead research author Robin Voigt-Zuwala, PhD, an associate professor of medicine and the director of the Circadian Rhythm Research Laboratory at Rush University Medical Center in Chicago. "Our study found that exposure to light at night could be detrimental for brain health as well, particularly for individuals with risk factors for Alzheimer's disease, such as family history, APOE4+ genotype [the strongest genetic risk factor for Alzheimer's disease], or comorbid diseases that increase risk like cardiovascular disease."

Why Younger People May Be More Vulnerable

Using satellite-acquired data, the study authors calculated average nighttime light intensity by state and county (excluding Hawaii and Alaska) between 2012 and 2018. Drawing on Medicare data, they determined Alzheimer's disease presence in different regions and compared disease prevalence to the level of light intensity in each area. They also incorporated medical data about variables known or believed to be risk factors for Alzheimer's.

In comparing risk factors, Dr. Voigt-Zuwala and her colleagues found that Alzheimer's prevalence in people 65 and older was more strongly linked with nightly light pollution than with alcohol abuse, chronic kidney disease, depression , and obesity . Other risk factors, including diabetes , high blood pressure, and stroke , were more strongly connected with Alzheimer's than light pollution.

For people under 65, however, nighttime light intensity was the No. 1 influence associated with Alzheimer's. Because no other disease risk factor in this population was as strongly tied to this dementia, scientists suggested that younger people may be particularly sensitive to the effects of light exposure at night.

Voigt-Zuwala notes that younger people tend to have lifestyles that expose them to more light at night.

"Urban areas with the most light pollution tend to be dominated by younger individuals, and younger people tend to stay up later for social activities," she says. "Light exposure during the normal rest period will disrupt circadian rhythms and will have detrimental effects on health."

Circadian rhythms regulate much of our biology and behavior, and disruptions may lead to inflammation in the intestinal microbiome, promote gut leakiness, and make individuals less resilient to stressors and more prone to disease.

Less Sleep Equals Greater Dementia Risk

For Yuko Hara, PhD , the director of Aging and Alzheimer's Prevention at Cognitive Vitality, a program of the Alzheimer's Drug Discovery Foundation, this analysis aligns with previous research that suggested people in their fifties and sixties who got fewer than six hours of sleep per night had a significantly higher risk of dementia.

"Beta-amyloid, a biological marker for Alzheimer's disease, can start to accumulate in the brain decades before symptom onset," says Dr. Hara, who was not involved in the research. "It is during sleep when toxic proteins such as amyloid get flushed out of the brain. Thus, it may be especially important for middle-aged people to get a sufficient amount of sleep to prevent the accumulation of amyloid and other toxic proteins in the brain."

Study authors add that having the APOE4+ gene, a factor that influences early onset Alzheimer's disease, may play a role in the increased vulnerability to the effects of nighttime light exposure, but more research is needed to understand how this ties in.

Indoor Light at Night From Electronics May Also Pose Risks

Claire Sexton, DPhil , who serves as the senior director of scientific programs and outreach at the Alzheimer's Association, says that this new paper only takes into account outdoor nighttime light exposure, not indoor, which can also contribute to poor sleep.

Although not investigated in this paper, blue light from electronics may be a major source of trouble when it comes to sleep, according to the study authors.

"Blue light promotes wakefulness and alertness," says Hara. "When you use electronics in the evenings, they can lead to an inability to fall asleep. Most phones and computers have settings to block the blue light during evening hours."

Dr. Sexton, who was not involved in the latest research, stresses that the study is "very broad and nonspecific," and does not demonstrate that light pollution causes Alzheimer's disease.

"Much more research is needed before conclusions can be made," she says.

Limiting Light Pollution's Damaging Effects

Overall, the findings here support previous research, and age-old wisdom, showing that a proper's night rest is a key to health.

To keep light from disturbing your slumber, the study authors recommend the following:

• Install blackout curtains.
• Wear an eye mask.
• Remove any unnecessary lights outside the home.
• Use light bulbs outdoors that are warmer and less harsh.

Editorial Sources and Fact-Checking

Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy . We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.

Sources

1. Menéndez-Velázquez A et al. Light Pollution and Circadian Misalignment: A Healthy, Blue-Free, White Light-Emitting Diode to Avoid Chronodisruption. International Journal of Environmental Research and Public Health . February 7, 2022.
2. Voigt RM et al. Outdoor Nighttime Light Exposure (Light Pollution) Is Associated With Alzheimer's Disease. Frontiers in Neuroscience . September 6, 2024.
3. Bryant E. Study Reveals How APOE4 Gene May Increase Risk for Dementia. National Institute on Aging . March 16, 2021.
4. Voigt RM et al. Circadian Rhythms: A Regulator of Gastrointestinal Health and Dysfunction. Expert Review of Gastroenterology and Hepatology . March 25, 2019.
5. Sabia S et al. Association of Sleep Duration in Middle and Old Age With Incidence of Dementia. Nature Communications . April 20, 2021.
6. Dose J et al. APOE Genotype and Stress Response - a Mini Review. Lipids in Health and Disease . July 25, 2016.

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Don Rauf

Author

Don Rauf has been a freelance health writer for over 12 years and his writing has been featured in HealthDay, CBS News, WebMD, U.S. News & World Report, Mental Floss, United Press International (UPI), Health , and MedicineNet. He was previously a reporter for DailyRx.com where he covered stories related to cardiology, diabetes, lung cancer, prostate cancer, erectile dysfunction, menopause, and allergies. He has interviewed doctors and pharmaceutical representatives in the U.S. and abroad.

He is a prolific writer and has written more than 50 books, including Lost America: Vanished Civilizations , Abandoned Towns , and Roadside Attractions . Rauf lives in Seattle, Washington.

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