Outdoor Nighttime Light Exposure (Light Pollution) is Associated with Alzheimer's Disease

Abstract

Alzheimer's disease (AD) prevalence has increased in the last century which can be attributed to increased lifespan, but environment is also important. This study evaluated the relationship between outdoor nighttime light exposure and AD prevalence in the United States. Higher outdoor nighttime light was associated with higher prevalence of AD. While atrial fibrillation, diabetes, hyperlipidemia, hypertension, and stroke were associated more strongly with AD prevalence than nighttime light intensity, nighttime light was more strongly associated with AD prevalence than alcohol abuse, chronic kidney disease, depression, heart failure, and obesity. Startlingly, nighttime light exposure more strongly associated with AD prevalence in those under the age of 65 than any other disease factor examined. These data indicate a need to investigate how nighttime light exposure influences AD pathogenesis.

Fig. 1.. Higher average nighttime light intensity is associated with higher AD prevalence (2012–2018 average).

(a) AD prevalence by state. (b) Average nighttime light intensity by state. (c) Average nighttime light intensity state rankings. 1/5 = darkest average nighttime light intensity through 5/5 = brightest average nighttime light intensity. (d) AD prevalence by state average nighttime light intensity rankings. ANOVA revealed a statistically significant difference in AD prevalence between groups (F(4,43)=13.50, p<0.0001). Multiple comparisons testing found that the states with the lowest average light intensity had statistically significant lower AD prevalence than states with higher average nighttime light intensity: 1/5 vs. 2/5 (p=0.031), 1/5 vs. 3/5 (p<0.001), 1/5 vs. 4/5 (p<0.001), 1/5 vs. 5/5 (p<0.001), and 2/5 vs. 5/5 (p=0.010). *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001. (e) Pearson correlation analysis between AD prevalence and nighttime light intensity revealed a positive relationship (r(46)=0.557. p<0.001). The circle size indicates state population.

Fig. 2:. Higher county average nighttime light intensity is associated with higher county AD prevalence (2012–2018).

(a) Average nighttime light intensity county rankings. AD prevalence by state average nighttime light intensity rankings. 1/5 = darkest average nighttime light intensity through 5/5 = brightest average nighttime light intensity. (b) AD prevalence by county average nighttime light intensity rankings. ANOVA: F(3,42)=10.750, p<0.001. Multiple comparisons testing revealed differences between groups with lower average light intensity and groups with higher average light intensity: 1/4 vs. 3/4 (p<0.01), 1/4 vs. 4/4 (p<0.001), 2/4 vs. 4/4 (p<0.01). (c) Pearson correlation analysis between AD prevalence and nighttime light intensity: r(44)=0.599, p<0.001. p<0.05, **p<0.01, ***p<0.001, ****p<0.0001. Circle size reflects state population.