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Bright Outdoor Light Exposure Overnight Raises Risk of Strokes

Living where outdoor lights are bright overnight can increase the possibility of either ischemic or hemorrhagic stroke.

You may have heard advice to lower light levels as bedtime approaches. People exposed to bright light indoors have lower levels of melatonin, a hormone essential for sleep. But interior lighting is not the only problem. Outdoor light pollution has become common worldwide. Most cities use bright light outdoors at night so people can travel safely. But when people are exposed to artificial outdoor light at night, they may experience unexpected harmful effects.

Studying the Effects of Outdoor Light Overnight:

Chinese researchers analyzed light exposure and medical records of more than 28,000 people in Ningbo, China (Stroke, April 2024). They used satellite maps to figure out where the street lights and other nighttime light sources were brightest. After six years of follow-up, those with the highest exposure to outdoor light overnight were 43 percent more likely to develop cerebrovascular disease than those with least exposure. That includes both ischemic and hemorrhagic strokes.

Air Pollution Is an Independent Risk Factor:

Air pollution has also been linked to a higher risk for Parkinson disease as well as heart problems. Consequently, the researchers checked its effects in Ningbo. They found that it too increased the risk for strokes.

People who were exposed to the highest levels of particulates from burning wood, gasoline, oil or diesel fuel were 41 percent more likely to develop cerebrovascular disease than those with the lowest exposures. The investigators suggest that air pollution, covering most particle sizes, may increase inflammation. This in turn could contribute to atherosclerosis or high blood pressure, both risk factors for strokes.

The hazards of air pollution and light pollution appear to be independent.

According to the lead researcher,

“Our study suggests that higher levels of exposure to outdoor artificial light at night may be a risk factor for cerebrovascular disease…Therefore, we advise people, especially those living in urban areas, to consider reducing that exposure to protect themselves from its potential harmful impact.”

Learn More:

We discussed ways to protect yourself and your family from indoor air pollution with Dr. Richard Corsi.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies..
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  • Wu Y et al, "Outdoor light at night, air pollution, and risk of cerebrovascular disease: A cohort study in China." Stroke, April 2024. DOI: 10.1161/STROKEAHA.123.044904
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