New Delhi: Night-time pollution from streetlights and illuminated signs has been linked with developing Alzheimer’s disease because of its effects on people’s sleep and biological clocks, according to a study that analysed light pollution maps in 48 US states. Researchers said that night-time light pollution may, therefore, be an important risk factor for developing the ageing-related disorder.
However, more studies are needed as the combined effects of both outdoor and indoor night-time light exposure are important to fully understand how they impact the development of Alzheimer’s disease, the researchers from Rush University Medical Center, US, said.
Irregular sleep patterns, including disturbances, is a common feature capable of triggering mild cognitive impairment, which is the the stage preceding dementia, with Alzheimer’s disease being the most common form.
Dementia is marked by affected memory, thinking and decision-making, thereby steadily deteriorating one’s daily functioning.
Known risk factors for developing dementia include metabolic conditions, such as diabetes and high blood pressure, and depression.
In this study, published in the journal Frontiers in Neuroscience, the researchers looked at the light pollution maps along with residents’ data taken from medical records. The data were related to risk factors for developing Alzheimer’s disease.
The researchers found that among people aged 65 and older, Alzheimer’s disease was more strongly correlated with nightly light pollution than other factors, including depression and obesity.
However, risk factors like diabetes, high blood pressure, and stroke were found to be more strongly linked with Alzheimer’s disease than light pollution.
Among people aged below 65, the researchers found that a higher intensity in night-time light was related to more people being affected by Alzheimer’s disease than any other risk factor they analysed in the study.
The results suggest that people younger than 65 years may be particularly sensitive to the effects of light exposure at night, the researchers said.
However, they were unclear as to why younger people could be more vulnerable, even as individual responses to light, along with their genetic risk of Alzheimer’s disease, could play a role, they said.
“Certain genotypes,  which influence early onset (Alzheimer’s disease), impact the response to biological stressors which could account for increased vulnerability to the effects of nighttime light exposure,” study author Robin Voigt-Zuwala, an associate professor at Rush University Medical Center, said.
“Additionally, younger people are more likely to live in urban areas and have lifestyles that may increase exposure to light at night,” Voigt-Zuwala said.
The authors said that possible processes by which light pollution may promote Alzheimer’s disease include disturbed sleep, disruptions to biological clock and increase in inflammation due to exposure to light.
They added that while the data suggest that being exposed to night-time light may contribute to developing Alzheimer’s disease, additional studies are needed, including those looking at effects of indoor and outdoor lights on developing the ageing-related condition.
