While light pollution is associated with increased risk of some disorders and diseases, this is the first time it had been associated with Alzheimer’s disease.

The study was conducted at Rush University System for Health and published in Frontiers in Neuroscience.

“Our research shows that there is an association in the U.S. between Alzheimer’s disease prevalence and exposure to light at night, particularly in those under the age of 65,” said lead investigator, Robin Voigt-Zuwala, PhD, an associate professor?at Rush. “Nightly light pollution — a modifiable environmental factor — may influence risk for Alzheimer’s.”

High U.S. light levels

While legislation in some states aims to reduce light pollution, levels of nighttime light remain high in many parts of the country.

In studying light pollution maps, researchers looked at the lower 48 states and incorporated medical data associated with Alzheimer’s disease risk factors and divided the groups by light intensity. In the five groups, they found that light intensity was correlated with Alzheimer’s disease prevalence even when some well-established disease factors were not.

While the cause is unknown, higher nighttime light intensity was associated with a greater Alzheimer’s disease prevalence than any other risk factor examined in the study for those under the age of 65, suggesting that younger people may be more sensitive to the effects of light exposure at night.

“Certain genes can influence early-onset Alzheimer’s,and these same genes may cause increased vulnerability to the effects of nighttime light exposure,” Voigt-Zuwala explained. “Additionally, younger people are more likely to live in urban areas and have lifestyles that may increase exposure to light at night.”

Reducing light exposure

Exposure to light influences the body’s natural sleep-wake pattern, which is called a circadian rhythm. Exposure to light at night can disrupt a person’s circadian rhythm, which can promote inflammation and make a person less resilient and more prone to disease. Researchers did not examine light inside the home at night or how it might impact health.

Voigt-Zuwala said, “The good news is that simple changes can be made with minimal effort to reduce exposure to light at night — adding black out curtains or sleeping with an eye mask.”

The research results are limited to a subset of the population and further testing is needed to better understand the connection between evening outdoor light and Alzheimer’s disease.