Shocking new study reveals that nighttime light pollution may increase the risk of Alzheimer’s, with younger adults most affected.
Study: Exposure to light at night (light pollution) is associated with Alzheimer’s disease. Image credit: New Africa/Shutterstock.com
In a recent study published in Frontiers of Neurosciencea group of researchers investigated the relationship between nighttime exposure to outdoor light and the prevalence of Alzheimer’s disease (AD) (a progressive brain disorder leading to memory loss and cognitive decline) in the United States.
Background
For much of history, light came from fire-based sources until the advent of gas and electric lighting in the 18th and 19th centuries. Today, artificial lighting is widespread, enhancing safety and convenience, but excessive light at night, known as light pollution, blocks natural skylight and poses health risks.
It is linked to sleep disorders, obesity, depression and potentially neurodegenerative diseases such as Alzheimer’s. Further research is needed to understand how exposure to light at night may contribute to Alzheimer’s disease and its impact on neurodegeneration.
About the study
The present study used de-identified Medicare data from 2012 to 2018 to assess the relationship between nighttime light exposure and AD prevalence, including both sexes.
Data were obtained from the Centers for Medicare and Medicaid Services (CMS), focusing on fee-for-service beneficiaries over age 65, people with certain disabilities, and people with end-stage renal disease. Differences influenced geographic variations in the prevalence of AD in health care resources and diagnostic practices.
Obesity data comes from the CDC’s Behavioral Risk Factor Surveillance System (BRFSS), which tracks self-reported obesity in adults.
Nighttime light exposure data were obtained from the National Aeronautics and Space Administration (NASA)/National Polar-orbiting Partnership Bidirectional Reflectance Distribution Function Visible Infrared Imaging Radiometer Suite (VIIRS)
(NPP Lunar BRDF)-Adjusted Nighttime Lights composites and irradiance levels were averaged for each state and county over the study period.
Statistical analyzes included Analysis of Variance (ANOVA) and correlation analysis to assess the relationship between nocturnal light exposure and AD prevalence. A linear mixed model was applied to account for repeated measures at the state and county level.
Covariates such as race, age, sex, and biological factors such as atrial fibrillation (an irregular, fast heartbeat that can cause brain and heart problems), diabetes, obesity were also included in the model.
Study results
The relationship between average nighttime light intensity and AD prevalence was examined using Medicare data from 2012 to 2018, alongside satellite data on nighttime light exposure. States were ranked by their average nighttime light intensity and divided into five groups, from darkest to brightest.
Statistical analysis revealed a significant difference in AD prevalence between these groups, with brighter states showing higher AD prevalence. A Pearson correlation analysis further confirmed this association, demonstrating a positive relationship between nighttime light intensity and AD prevalence in the United States. This association applies to people over and under 65 years of age.
When the data were examined year by year, the same positive relationship between nighttime light and AD prevalence was observed, reinforcing the findings. A linear mixed model showed a significant association between nighttime light intensity and AD prevalence when all subjects were considered, as well as within subgroups stratified by age, sex, and race.
The relationship was particularly strong in some ethnic groups, such as Native Americans. The effect of nocturnal light exposure remained significant even after accounting for variants known to influence AD risk, such as alcohol abuse, depression, heart failure, chronic kidney disease, and obesity.
However, other variants, such as atrial fibrillation, diabetes, and stroke, were more strongly associated with AD prevalence than light exposure.
Counties, which tend to be more homogeneous than entire states, were also analyzed. The relationship between nighttime light intensity and AD prevalence was assessed in each state’s largest city by comparing county-level nighttime light intensity with Medicare chronic conditions data.
This analysis confirmed the association between nighttime light and AD prevalence at the county level. Counties with the highest nighttime light intensity had significantly higher AD prevalence than those with the lowest light intensity.
Correlation analyzes also demonstrated a positive relationship between light intensity and the prevalence of AD, both in subjects over 65 years of age and in subjects under 65 years of age.
A linear mixed-effects model further supported the significant association between nocturnal light exposure and AD prevalence at the county level.
This relationship persisted across different age groups, with particularly strong effects seen in those under 65. These county-level findings mirror those at the state level, strengthening evidence for a positive association between nighttime light exposure and AD prevalence.
conclusions
In summary, the study found that higher average nighttime light intensity, or light pollution, was associated with a higher prevalence of AD during 2012-2018, affecting both sexes and most age and racial groups.
Nocturnal light exposure had a stronger association with AD than risk factors such as depression, alcohol abuse and obesity, although it was weaker compared to conditions such as diabetes and stroke. Those under 65 were particularly sensitive to light exposure.
