Researchers at Guangzhou Medical University conducted a comprehensive study tracking approximately 88,000 individuals over eight years, revealing a significant correlation between daytime light exposure and reduced rates of dementia.

Zheng et al. displayed findings that link higher daytime light exposure to a decreased risk of dementia. Image credit: Zheng et al., doi: 10.1002/gps3.70039.

“Dementia is recognized as the leading neurodegenerative disease globally, characterized by a progressive decline in cognitive function and deterioration in daily living activities,” stated co-senior author Dr. Hongliang Feng and colleagues.

“With the aging global population, the incidence of dementia is rising swiftly, and effective treatments remain scarce, creating significant health and socio-economic challenges.”

“Thus, there is a pressing need to identify protective factors and create effective prevention strategies.”

“The natural light-dark cycle, highlighted by darkness during the night and brightness throughout the day, is a crucial environmental signal that governs endogenous circadian rhythms.”

“This circadian regulation influences various aspects of physiology, behavior, and cognitive functions.”

“Conversely, disturbances in circadian rhythm are prevalent among individuals with dementia and are linked to an elevated risk of developing dementia in the general population.”

In this pivotal study, the authors monitored 87,577 adults from the UK Biobank during a median follow-up period of 8.1 years.

Findings indicated that participants exposed to light levels of 1,000 lux or higher (approximately equivalent to the brightness of indirect outdoor light) had a roughly 16% lower risk of developing dementia compared to those in dimly lit settings.

Notably, the benefits escalated with increased light intensity. Individuals who spent at least 42 minutes daily in environments with 5,000 lux or higher experienced an approximate 17% reduction in their dementia risk.

It’s crucial to note that light exposure was measured using a wrist-worn sensor continuously for seven days in real-world conditions, rather than relying on self-reported data.

“Our findings position daytime light exposure as a novel, robust, and quantifiable indicator of dementia risk,” the researchers concluded.

When evaluated alongside 15 known dementia predictors using a machine learning model, inadequate daytime light was found to be more predictive than factors such as obesity, alcohol consumption, air pollution, and traumatic brain injury.

Conservation groups illustrated the strongest links, particularly among individuals with chronic nighttime light exposure, known as night owls, and those carrying the ApoE ε4 genetic mutation, which is the most significant known genetic risk factor for Alzheimer’s disease.

In these vulnerable populations, dementia risk reduction reached as high as 41%.

The researchers propose that daytime light may contribute to stabilizing the body’s circadian rhythms and preserving certain brain structures.

Conversely, exposure to light at night displayed no notable association with dementia risk.

“The insights from this study could shape future research and public health guidelines, advocating for light-based interventions that promote increased daytime light exposure as an economical strategy to enhance brain health, particularly in at-risk groups,” the scientists concluded.

Read their paper published in the journal General Psychiatry.

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Nana Jen et al. 2026. Association between daytime and nighttime light exposure as measured by wearable devices and dementia risk: a prospective cohort study. General Psychiatry 39 (3): e70039; doi: 10.1002/gps3.70039