Startling new study reveals that nighttime light pollution may increase the risk of Alzheimer’s, particularly affecting younger adults.
Study: Nighttime exposure to light outdoors (light pollution) has been linked to Alzheimer’s disease. Image credits: New Africa/Shutterstock.com
From a recent study published in the Frontiers of neurosciencea group of researchers examined the relationship between outdoor nighttime light exposure and the prevalence of Alzheimer’s disease (AD) (a progressive brain disorder that leads to memory loss and cognitive decline) in the United States.
Background
For much of history, light came from fire sources, until gas and electric lighting emerged in the 18th and 19th centuries. Today, artificial lighting is widespread, increasing safety and convenience, but excessive light at night, known as light pollution, blocks natural sky light and poses health risks.
It is linked to sleep disruption, obesity, depression and possibly neurodegenerative diseases such as Alzheimer’s disease. Further research is needed to understand how nighttime light exposure may contribute to Alzheimer’s disease and its impact on neurodegeneration.
About the study
The current study used deidentified Medicare data from 2012 to 2018 to assess the relationship between nighttime light exposure and AD prevalence, including both genders.
Data were obtained from the Centers for Medicare and Medicaid Services (CMS), focusing on fee-for-service beneficiaries over age 65, individuals with certain disabilities, and those with end-stage renal disease. Differences influenced geographic variations in AD prevalence in health care 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) Visible Infrared Imaging Radiometer Suite (VIIRS) / National Polar-orbiting Partnership Bidirectional Reflectance Distribution Function
(NPP Lunar BRDF)-adjusted Nighttime Lights composites and radiation levels were averaged for each state and province over the study period.
Statistical analyzes included analysis of variance (ANOVA) and correlation analysis to evaluate the relationship between nighttime light exposure and the prevalence of AD. A linear mixed model was applied to account for repeated measures at the state and county levels.
Covariates such as race, age, gender, and biological factors such as atrial fibrillation (an irregular, fast heartbeat that can cause strokes and heart problems), diabetes, and 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, in addition to 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 correlation applied to persons over 65 years of age.
When the data was examined year after 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 among certain ethnic groups, such as Native Americans. The effect of nighttime light exposure remained significant even after taking into account covariates known to influence AD risk, such as alcohol abuse, depression, heart failure, chronic kidney disease and obesity.
However, other covariates, such as atrial fibrillation, diabetes, and stroke, were more strongly associated with AD prevalence than light exposure.
An analysis was also conducted of counties, which tend to be more homogeneous than entire states. The relationship between nighttime light intensity and AD prevalence was assessed in the largest city in each state, comparing county-level nighttime light intensity with chronic Medicare data.
This analysis confirmed the association between nighttime light and AD prevalence at the provincial level. Counties with the highest nighttime light intensity had significantly higher AD prevalence than those with the lowest light intensity.
Correlation analyzes also showed a positive relationship between light intensity and AD prevalence, both in persons over 65 years of age and in persons under 65 years of age.
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 people under 65. These county-level findings mirrored 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 genders and most age and racial groups.
Exposure to nighttime light had a stronger link 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.