a new national study suggested.
Analyses of state and county light pollution data and Medicare claims showed that areas with higher average nighttime light intensity had a greater prevalence of Alzheimer’s disease.
Among people aged 65 years or older, Alzheimer’s disease prevalence was more strongly associated with nightly light pollution exposure than with alcohol misuse, chronic kidney disease, depression, or obesity.
In those younger than 65 years, greater nighttime light intensity had a stronger association with Alzheimer’s disease prevalence than any other risk factor included in the study.
“The results are pretty striking when you do these comparisons and it’s true for people of all ages,” said Robin Voigt-Zuwala, PhD, lead author and director, Circadian Rhythm Research Laboratory, Rush University, Chicago, Illinois.
The study was published online in Frontiers of Neuroscience.
Shining a Light
Exposure to artificial outdoor light at night has been associated with adverse health effects such as sleep disruption, obesity, atherosclerosis, and cancer, but this is the first study to look specifically at Alzheimer’s disease, investigators noted.
Two recent studies reported higher risks for mild cognitive impairment among Chinese veterans and late-onset dementia among Italian residents living in areas with brighter outdoor light at night.
For this study, Dr. Voigt-Zuwala and colleagues examined the relationship between Alzheimer’s disease prevalence and average nighttime light intensity in the lower 48 states using data from Medicare Part A and B, the Centers for Disease Control and Prevention, and NASA satellite–acquired radiance data.
The data were averaged for the years 2012-2018 and states divided into five groups based on average nighttime light intensity.
The darkest states were Montana, Wyoming, South Dakota, Idaho, Maine, New Mexico, Vermont, Oregon, Utah, and Nevada. The brightest states were Indiana, Illinois, Florida, Ohio, Massachusetts, Connecticut, Maryland, Delaware, Rhode Island, and New Jersey.
Analysis of variance revealed a significant difference in Alzheimer’s disease prevalence between state groups (P < .0001). Multiple comparisons testing also showed that states with the lowest average nighttime light had significantly different Alzheimer’s disease prevalence than those with higher intensity.
The same positive relationship was observed when each year was assessed individually and at the county level, using data from 45 counties and the District of Columbia.
Strong Association
The investigators also found that state average nighttime light intensity is significantly associated with Alzheimer’s disease prevalence (P = .006). This effect was seen across all ages, sexes, and races except Asian Pacific Island, the latter possibly related to statistical power, the authors said.
When known or proposed risk factors for Alzheimer’s disease were added to the model, atrial fibrillation, diabetes, hyperlipidemia, hypertension, and stroke had a stronger association with Alzheimer’s disease than average nighttime light intensity.
Nighttime light intensity, however, was more strongly associated with Alzheimer’s disease prevalence than alcohol abuse, chronic kidney disease, depression, heart failure, and obesity.
Moreover, in people younger than 65 years, nighttime light pollution had a stronger association with Alzheimer’s disease prevalence than all other risk factors (P = .007).
The mechanism behind this increased vulnerability is unclear, but there may be an interplay between genetic susceptibility of an individual and how they respond to light, Dr. Voigt-Zuwala suggested.
“APOE4 is the genotype most highly associated with Alzheimer’s disease risk, and maybe the people who have that genotype are just more sensitive to the effects of light exposure at night, more sensitive to circadian rhythm disruption,” she said.
The authors noted that additional research is needed but suggested light pollution may also influence Alzheimer’s disease through sleep disruption, which can promote inflammation, activate microglia and astrocytes, and negatively alter the clearance of amyloid beta, and by decreasing the levels of brain-derived neurotrophic factor.