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From the Journals

Study Links Nighttime Light to Alzheimer's Prevalence

Nighttime light pollution strongly linked to Alzheimer's disease risk in individuals younger than 65, surpassing traditional risk factors, new study finds.

Conexiant

A new study has reported an association between outdoor nighttime light exposure and Alzheimer's disease prevalence in the United States. Researchers analyzed Medicare data, satellite-acquired light intensity measurements, and Centers for Disease Control and Prevention Behavioral Risk Factor Surveillance System data from 2012 to 2018 for the lower 48 states.

Key Findings

Exposure to higher outdoor nighttime light intensity was correlated with higher Alzheimer's disease (AD) prevalence (regression coefficient = 0.283, standard error [SE] = 0.102, 95% confidence interval [CI] = 0.082-0.485, P = .006, R² = 0.382). The association persisted across age groups, sexes, and most racial/ethnic groups examined. For individuals younger than 65 years, nighttime light exposure showed a stronger association with AD prevalence than other examined disease risk factors. 

County-level analysis revealed a similar positive correlation (r(44) = 0.599, P < .001).

Study Methods and Detailed Results

The study, published in Frontiers in Neuroscience, utilized Medicare Chronic Conditions data for AD prevalence and NASA's VIIRS/NPP Lunar BRDF-Adjusted Nighttime Lights Yearly composites for light pollution measurements. States were ranked and divided into five groups based on average nighttime light intensity.

Analysis of variance showed significant differences in AD prevalence between state groups based on light intensity (F(4, 43) = 13.500, P < .001). Pearson correlation analysis demonstrated positive relationships at both state (r(46) = 0.557, P < .001) and county levels.

Subgroup analysis revealed:

  • Age 65+: regression coefficient = 0.328, SE = 0.125, P = .009
  • Age <65: regression coefficient = 0.211, SE = 0.060, P = .001
  • Males: regression coefficient = 0.265, SE = 0.085, P = .002
  • Females: regression coefficient = 0.296, SE = 0.118, P = .013.

The association between AD and nighttime light intensity remained significant when accounting for various covariates, such as:

  • Alcohol abuse: regression coefficient = 0.266, SE = 0.104, P = .011
  • Chronic kidney disease: regression coefficient = 0.289, SE = 0.089, P = .001
  • Depression: regression coefficient = 0.295, SE = 0.099, P = .003
  • Heart failure: regression coefficient = 0.222, SE = 0.072, P = .002.

However, atrial fibrillation, diabetes, hyperlipidemia, hypertension, and stroke showed stronger associations with AD prevalence than light intensity.

For individuals under 65, the association remained significant even when considering all covariates (estimate = 0.174, SE = 0.064, P = .007).

The study also examined racial/ethnic subgroups:

  • Hispanic: regression coefficient = 0.488, SE = 0.198, P = .014
  • Native American: regression coefficient = 1.031, SE = 0.190, P < .001
  • Non-Hispanic Black: regression coefficient = 0.671, SE = 0.182, P < .001
  • Non-Hispanic White: regression coefficient = 0.306, SE = 0.101, P = .003.

County-level analysis yielded similar results:

  • All individuals: regression coefficient = 0.040, SE = 0.003, P < .001, R² = 0.304
  • Age 65+: regression coefficient = 0.052, SE = 0.004, P < .001, R² = 0.304
  • Age <65: regression coefficient = 0.019, SE = 0.002, P < .001, R² = 0.480.

The researchers discussed potential mechanisms by which light at night may influence AD, including sleep disruption, circadian rhythm disruption, and biochemical changes. Sleep disruption can activate microglia and astrocytes, promote inflammation, and alter amyloid beta clearance. In mice, exposure to dim light increases production of pro-inflammatory cytokine interleukin 1β and decreases levels of brain-derived neurotrophic factor in the hippocampus.

The study noted that AD prevalence has increased in recent decades, paralleling the increase in light pollution since the widespread adoption of electric lighting in the early 1900s. The authors suggested that as major AD risk factors are better managed, environmental factors like nighttime light exposure may have a more substantial influence on AD pathogenesis in the future.

The researchers noted several limitations of the study, including reliance on Medicare data, use of current residences rather than lifetime exposure data, and focus on AD prevalence rather than incidence; the study also did not account for indoor light exposure. They concluded that while their data and preclinical studies suggest exposure to light at night may influence AD, additional clinical and population health studies are needed.

The authors declared that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.