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

A surprising new study finds that night-time light pollution may spike the risk of Alzheimer's disease, with young adults most affected.

study: Nighttime outdoor light exposure (light pollution) is linked to Alzheimer's diseaseImage credit: New Africa/Shutterstock.com

In a recently published study, The cutting edge of neuroscienceA group of researchers investigated the relationship between exposure to outdoor light at night and the incidence of Alzheimer's disease (AD), a progressive brain disorder that leads to memory loss and cognitive decline, in the United States.

background

Historically, lighting was based on fire, followed by gas and electric lighting in the 18th and 19th centuries. Today, artificial lighting is widespread and offers safety and convenience, but excessive light at night, known as light pollution, can block out natural celestial light and pose health risks.

This can lead to sleep disorders, obesity, depression, and neurodegenerative diseases like Alzheimer's. More research is needed to understand how exposure to light at night affects Alzheimer's disease and how it influences neurodegeneration.

About the Research

This study used de-identified Medicare data from 2012 to 2018 to evaluate the relationship between nighttime light exposure and the prevalence of AD in both men and women.

Data were obtained from the Centers for Medicare and Medicaid Services (CMS) and focused on fee-for-service recipients aged 65 years and older, individuals with certain disabilities, and patients with end-stage renal disease. Differences influenced geographic variation in prevalence of AD in health care resources and diagnostic practices.

Obesity data came from the CDC's Behavioral Risk Factor Surveillance System (BRFSS), which tracks self-reported obesity among adults.

Nighttime light exposure data were obtained from the National Aeronautics and Space Administration's (NASA) Visible Infrared Imaging Radiometer (VIIRS)/US Polar-orbiting Satellite Partnership Bidirectional Reflectance Distribution Function.

(NPP Lunar BRDF) Adjusted nighttime light composite and radiance levels were averaged for each state and county over the study period.

Statistical analyses included analysis of variance (ANOVA) and correlation analyses to assess the relationship between nighttime light exposure and prevalence of AD. Linear mixed models were applied to account for repeated measures at state and county levels.

Covariates such as race, age, sex and biological factors such as atrial fibrillation (an irregular, fast heartbeat that can lead to stroke or heart disease), diabetes and obesity were also included in the model.

Research findings

The relationship between average nighttime light intensity and prevalence of Alzheimer's disease was examined using Medicare data and satellite data on nighttime light exposure from 2012 to 2018. States were ranked by average nighttime light intensity and divided into five groups, from dimmest to brightest.

Statistical analysis revealed significant differences in the prevalence of AD between these groups, with brighter states having a higher prevalence of AD. Pearson correlation analysis further confirmed this association, showing a positive correlation between nighttime light intensity and the prevalence of AD across the United States. This correlation held true for individuals aged 65 years and older and individuals aged 65 years and younger.

When the data was examined by year, the same positive correlation between night-time light and prevalence of AD was found, supporting the findings. Linear mixed models showed significant associations between night-time light intensity and prevalence of AD when considering all individuals and subgroups by age, sex, and race.

This association was particularly strong among certain ethnic groups, such as Native Americans. The effect of nighttime light exposure remained significant even after accounting for covariates known to influence AD ​​risk, including 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.

Analyses were also conducted for counties, which tend to be more homogeneous than states overall.The relationship between nighttime light intensity and prevalence of AD was assessed in the largest city in each state, comparing county-level nighttime light intensity with Medicare chronic disease data.

This analysis confirmed the association between night-time light and AD prevalence at the county level: counties with the highest night-time light intensity had significantly higher AD prevalence than counties with the lowest light intensity.

Correlation analysis also showed a positive correlation between light intensity and the prevalence of AD in both people aged 65 years or older and people aged <65 years.

Linear mixed-effects models further supported a significant association between night-time light exposure and AD prevalence at the county level.

This relationship persisted across age groups, with particularly strong effects seen in people under age 65. These county-level findings are consistent with state-level findings and strengthen the evidence for a positive association between nighttime light exposure and AD prevalence.

Conclusion

In summary, this study found that increases in average night-time light intensity, or light pollution, were associated with increased prevalence of AD from 2012 to 2018, affecting both sexes and most age and racial groups.

Exposure to light at night was more strongly associated with AD than risk factors such as depression, alcohol abuse, and obesity, but the association was weaker than with diseases such as diabetes and stroke. People under 65 were particularly sensitive to light exposure.