Study finds link between nighttime light exposure and increased Alzheimer's disease risk

By Vijay Kumar MalesuReviewed by Lily Ramsey, LLMSep 10 2024

Startling new study reveals nighttime light pollution may spike Alzheimer’s risk, with younger adults most affected.

Study: Outdoor nighttime light exposure (light pollution) is associated with Alzheimer’s disease. Image Credit: New Africa/Shutterstock.com

In a recent study published in the Frontiers of Neuroscience, a group of researchers investigated the relationship between outdoor nighttime light exposure and Alzheimer’s disease (AD) (A progressive brain disorder leading to memory loss and cognitive decline) prevalence in the United States.

Background 

For much of history, light came from fire-based sources until gas and electric lighting emerged 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 celestial light and poses health risks.

It is linked to sleep disruption, obesity, depression, and potentially neurodegenerative diseases like Alzheimer’s. Further research is needed to understand how nighttime light exposure may contribute to Alzheimer's and its impact on neurodegeneration.

About the study 

The present study utilized 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 65, individuals with certain disabilities, and those with end-stage renal disease. Differences influenced geographic variations in AD prevalence in healthcare resources and diagnostic practices.

Obesity data were sourced from the CDC’s Behavioral Risk Factor Surveillance System (BRFSS), which tracks self-reported adult obesity.

Nighttime light exposure data were acquired from National Aeronautics and Space Administration (NASA)’s Visible Infrared Imaging Radiometer Suite (VIIRS)/ National Polar-orbiting Partnership Bidirectional Reflectance Distribution Function

(NPP Lunar BRDF)-Adjusted Nighttime Lights composites, and radiance levels were averaged for each state and county over the study period.

Statistical analyses included Analysis of Variance (ANOVA) and correlation analysis to evaluate the relationship between nighttime light exposure and AD prevalence. A linear mixed model was applied to account for repeated measures at the state and county levels.

Covariates such as race, age, sex, and biological factors like atrial fibrillation (An irregular, rapid heartbeat that can cause strokes 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 the darkest to the 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 across the United States. This correlation held true for individuals over and under the age of 65.

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 considering all individuals, as well as within subgroups divided by age, sex, and race.

The relationship was particularly strong in certain ethnic groups, like Native Americans. The effect of nighttime light exposure remained significant even after accounting for co-variates known to influence AD risk, such as alcohol abuse, depression, heart failure, chronic kidney disease, and obesity.

However, other co-variates, like atrial fibrillation, diabetes, and stroke, were more strongly associated with AD prevalence than light exposure.

An analysis of counties, which tend to be more homogeneous than entire states, was also conducted. The relationship between nighttime light intensity and AD prevalence was assessed in the largest city of each state, 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 analyses also demonstrated a positive relationship between light intensity and AD prevalence, both in individuals over 65 and those under 65.

A linear mixed-effects model further supported the significant association between nighttime light exposure and AD prevalence at the county level.

This relationship persisted across different age groups, with particularly strong effects observed in those under 65. These findings at the county level mirrored those at the state level, strengthening the evidence for a positive link between nighttime light exposure and AD prevalence.

Conclusions 

To summarize, the study found that higher average nighttime light intensity, or light pollution, was linked to a higher prevalence of AD across 2012-2018, affecting both sexes and most age and racial groups.

Nighttime light exposure had a stronger association with AD than risk factors like depression, alcohol abuse, and obesity, though it was weaker compared to conditions like diabetes and stroke. Those under 65 were particularly sensitive to light exposure.