Excessive light pollution may increase the risk of Alzheimer’s disease, especially in young people

In some parts of the world, the lights never go out. Streetlights, road lighting, and illuminated signs can deter crime, make roads safer, and beautify landscapes. However, undisturbed light has ecological, behavioral, and health consequences.

In the United States, some states have implemented laws to reduce light pollution. However, nighttime light levels remain high in many parts of the country. American researchers have studied the correlations between outdoor nighttime light pollution and Alzheimer’s disease (AD).

“We have demonstrated that in the United States, there is a positive correlation between the prevalence of Alzheimer’s disease and light exposure at night, particularly among people under 65 years of age,” said the study’s first author, Dr. Robin Voigt-Zuwala, associate professor at Rush University Medical Center. “Nighttime light pollution, a modifiable environmental factor, may be an important risk factor for Alzheimer’s disease.”

The work appears in Frontiers of neuroscience.

High intensity, high risk

The researchers studied light pollution maps of the 48 contiguous U.S. states and incorporated medical data on variables known or thought to be risk factors for Alzheimer’s disease into their analysis. They generated data on nighttime light intensity for each state and divided it into five groups, from lowest to highest nighttime light intensity.

Their results showed that among people aged 65 and older, the prevalence of Alzheimer’s disease was more strongly correlated with nighttime light pollution than with other risk factors, including alcohol abuse, chronic kidney disease, depression and obesity. Other risk factors, such as diabetes, high blood pressure and stroke, were more strongly associated with Alzheimer’s disease than light pollution.

However, in people younger than 65, the researchers found that higher nighttime light intensity was associated with a higher prevalence of Alzheimer’s disease than any other risk factor examined in the study. This could suggest that younger people may be particularly susceptible to the effects of nighttime light exposure, the researchers said.

It’s unclear why younger people are more vulnerable, but it could be due to individual differences in light sensitivity. “Certain genotypes, which influence the early onset of Alzheimer’s disease, impact the response to biological stressors, which could explain increased vulnerability to the effects of nighttime light exposure,” Voigt-Zuwala explained. “In addition, younger people are more likely to live in urban areas and have lifestyles that may increase their exposure to light at night.”

Curtains and masks

The researchers hope their findings can help raise awareness of the potential risks of nighttime light. “Awareness of this link should empower people, especially those with risk factors for Alzheimer’s disease, to make simple lifestyle changes,” Voigt-Zuwala said. “The simplest changes to implement include using blackout curtains or wearing an eye mask when sleeping. These measures are particularly helpful for people living in areas with high light pollution.”

Additionally, exposure to light inside the home may be as important as exposure from outside. While the researchers did not examine the effects of indoor light in the current study, they said that blue light has the greatest impact on sleep, and that using blue light filters, switching to warm light, and installing dimmers in the home could effectively reduce light exposure.

The researchers stressed that their findings are based on a subset of the U.S. population and that people don’t necessarily live their entire lives in areas with high light pollution, which could impact individual results. They also said more research is needed to better understand how nighttime light influences Alzheimer’s disease.