Researchers from Guangzhou Medical University monitored nearly 88,000 individuals for over eight years and identified a notable correlation between daytime light exposure and a decreased incidence of dementia. The study’s findings were published in General Psychiatry.
“Dementia, the most common neurodegenerative condition worldwide, is marked by a progressive decline in cognitive abilities and disruptions to daily functioning,” said study co-author Hongliang Feng.
As the global population ages, the rapidly increasing prevalence of dementia, coupled with the scarcity of effective treatments, presents an escalating challenge for healthcare systems and socioeconomic frameworks.
Consequently, there is an urgent need to pinpoint protective factors and formulate efficient preventive strategies.
The natural light-dark cycle, defined by darkness at night and bright illumination during the day, is a foundational environmental element that aligns internal circadian rhythms.
This circadian synchronization governs physiological processes, behaviors, and cognitive performance.
Conversely, disruptions to circadian rhythms are frequently observed in individuals with dementia and are linked to a heightened risk of developing the condition within the general population.
In the study, the authors tracked data from 87,577 adults enrolled in the UK Biobank over an average follow-up period of 8.1 years.
The researchers discovered that individuals who spent their days under light levels exceeding 1,000 lux—comparable to the brightness of indirect outdoor daylight—had roughly a 16% lower risk of developing dementia relative to those in dimmer settings.
This beneficial effect intensified with greater light exposure: participants who spent at least 42 minutes daily in environments with 5,000 lux or more experienced a risk reduction of approximately 17%.
Notably, the researchers measured light exposure not via self-reports but through wrist-worn sensors worn continuously for seven days in real-world conditions.
“These findings position daytime light exposure as a novel, reliable, and quantifiable indicator of dementia risk,” the scientists stated.
When compared against 15 widely recognized predictive factors for dementia using a machine-learning model, insufficient bright daytime light outperformed variables such as obesity, alcohol consumption, air pollution, and traumatic brain injury.
The strongest protective association was observed in three subgroups: individuals also exposed to intense nighttime light, those with an evening chronotype (“night owls”), and carriers of the APOE ε4 gene variant—the most significant known genetic risk factor for Alzheimer’s disease.
Within these groups, the reduction in dementia risk reached as high as 41%.
The researchers hypothesize that daylight may help stabilize the body’s circadian rhythms and preserve certain brain structures.
In contrast, nighttime light exposure showed no significant link to dementia risk.
“These results could inform future research into light-based therapies and public health recommendations advocating for increased daytime light exposure as a low-cost strategy to maintain brain health, particularly among high-risk populations,” the scientists concluded.
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