Outdoor light pollution correlates with risk of Alzheimer's, study finds

(CN) — Since the widespread electrification of cities began at the turn of the 20th century, the proliferation of light pollution has visibly changed the world.

While the most obvious effect is making the stars in the night sky less visible, scientists and governments have been concerned for decades about its adverse effects on the planet’s ecosystems and on human health.

Researchers at Rush University Medical Center in Chicago, Illinois say in a study published Thursday in the journal Frontiers found that areas in the United States with higher outdoor light pollution correspond to higher prevalence of Alzheimer’s disease.

Robin Voigt-Zuwala, the study’s corresponding author and an Associate Professor of Medicine, Anatomy, and Cell Biology at Rush University Medical Center, highlighted one part of the findings in particular: that for people under the age of 65, regardless of gender, light pollution correlated with Alzheimer’s higher than any other risk factor they examined, including alcohol abuse and chronic kidney disease.

“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 a statement. “Additionally, younger people are more likely to live in urban areas and have lifestyles that may increase exposure to light at night.”

In people over 65, Voigt-Zuwala and the team found that light pollution correlated more strongly than some effects, like chronic kidney disease, but less in others, like diabetes and high blood pressure.

The research team used publicly-available nighttime light pollution maps and medical data from Medicare in the lower 48 states and compared the light intensity figures with the rates of Alzheimer’s diagnosis. breaking the data down into five percentile ranges from lowest to highest light intensity.

Voigt-Zuwala also emphasized four imperfections and limitations in the data they used.

The Medicare data only covers individuals enrolled in certain parts of the program, and only reflect the individuals’ current places of residence without noting how long they had lived there. Moreover, the data only showed how many total cases of Alzheimer’s there were in a given area, regardless of time since diagnosis, not the rates of new cases in the examined time period.

Likewise, the data did not include indoor exposure from lightbulbs and electronic devices, which the authors noted is as important as the outdoor exposure they examined for a complete picture of any correlation or link between light pollution and Alzheimer’s.

The researchers hope their findings can help people potentially avoid triggering the disease.

“Awareness of the association should empower people — particularly those with risk factors for AD — to make easy lifestyle changes,” Voigt-Zuwala said. “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.”

While many researchers have found links between light pollution and poor health effects, especially on sleep quality and mental health, particularly sleep disruption, this latest study is the first to find a similar pattern with Alzheimer’s.

One study from Italy in 2023 found similar correlations between light pollution and dementia, and a few have more broadly examined neurodegeneration, but the Alzheimer’s subset of the field of research had otherwise gone unexplored.