Is Nighttime Light Pollution Exposure an Alzheimer Disease Risk Factor?

Outdoor nighttime light population may be associated with an increased prevalence of Alzheimer disease (AD), according to study results published in Frontiers in Neuroscience.

Although recent reports show an increase in light pollution as well as incidence and prevalence of AD in the United States, limited information is available on the link between light exposure at night and AD.

Researchers aimed to study the link between outdoor nighttime light exposure and AD prevalence in the US.

The researchers used satellite-acquired and Medicare data to measure average nighttime light intensity and AD prevalence, respectively, between 2012 and 2018. Each state in the US was categorized into 1 of 5 groups based on average nighttime light intensity (1 being the darkest and 5 being the brightest).

The researchers found a statistically significant difference in AD prevalence between the groups, ie, states with the darkest and brightest average nighttime light intensity (P <.001).

Using a linear mixed model, the researchers noted overall regression was statistically significant — average nighttime light intensity was significantly associated with AD prevalence (regression coefficient, 0.283; R², 0.382; P =.006).

In addition, average nighttime light intensity was associated with AD prevalence even after accounting for AD risk factors, such as alcohol abuse, chronic kidney disease, depression, heart failure, and obesity. These findings suggested that nighttime light intensity had a greater effect on AD prevalence than these risk factors. Whereas, covariates such as atrial fibrillation, diabetes, hyperlipidemia, hypertension, and stroke were more strongly associated with AD than nighttime light intensity.

Compared with individuals aged 65 and older, men and women, and all races except Asian Pacific Islander, those younger than age 65 were found to be more sensitive to the effects of nighttime light exposure (P =.007).

A county-wise analysis showed a statistically significant difference between counties with the lowest (darkest) vs highest (brightest) average nighttime light intensity (P <.001).

Limitations of the analysis included Medicare data collected were not comprehensive; lack of accounting for incidence of AD; and that light intensity data were collected from satellites, resulting in a lack of information on the effects of indoor light exposure.

Overall, the researchers concluded, “There is a positive association between [AD] prevalence and average outdoor nighttime light intensity in the United States;” however, “additional studies carefully evaluating indoor and outdoor light exposure and mechanistic evaluations are needed to fully understand the impact of nighttime light exposure and light pollution on AD.”