Nighttime Outdoor Light Exposure Linked to Stroke, Study Says

Consistent exposure to bright, artificial outdoor light at nighttime may damage brain health and raise the risk of stroke, according to new research.

Roughly 80% of the world’s population lives in light-polluted environments — a factor that may be impacting brain health and increasing stroke risks for those who aren’t properly shielding themselves from light during the night.

This is according to new research published in Stroke this week, which found that people with the highest levels of exposure to outdoor light at night had a 43% increased risk of developing cerebrovascular disease (a group of conditions that impact blood flow to the brain, including stroke) compared to those with the lowest levels of exposure.

Previous research has linked nighttime light exposure to cardiovascular risk factors and cancer, but this is the first study to draw a connection between light and brain health risks.

Researchers analyzed data from 28,302 adults living in China for the study. They assessed exposure to residential outdoor nighttime light using satellite images that mapped light pollution, and they confirmed cases of stroke by hospital medical records and death certificates. Of the participants, 1,278 people developed cerebrovascular disease, including 777 ischemic (clot-caused) stroke cases and 133 hemorrhagic (bleeding) stroke cases.

Artificial light sources mainly include fluorescent, incandescent, and LED light, according to the study. Overexposure to these light sources may suppress melatonin production and impair the body’s circadian rhythm by disrupting sleep patterns and shortening sleep duration, the authors wrote — ultimately leading to disease.

The study also looked at the impact of air pollution on cerebrovascular disease. It found that people with the highest levels of exposure to particulate matter 2.5 (emissions from combustion of gasoline, oil, diesel fuel, or wood) had a 41% increased risk of developing cerebrovascular disease compared to participants with the lowest levels of exposure.

Participants with the highest levels of exposure to PM10 (from dust and smoke) meanwhile had a 50% increased risk of developing cerebrovascular disease compared to those with the lowest exposure and those with the highest exposure to nitrogen oxide (emissions from cars, trucks, buses, power plants, and off-road equipment) had a 31% higher risk of developing cerebrovascular disease compared to those with the lowest exposure.

“We need to develop more effective policies and prevention strategies to reduce the burden of disease from environmental factors such as light as well as air pollution, particularly for people living in the most densely populated, polluted areas around the world,” said corresponding author Jian-Bing Wang, Ph.D., a researcher in public health and endocrinology, in a release. “We advise people, especially those living in urban areas, to consider reducing that exposure to protect themselves from its potential harmful impact.”


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