Most people spend much of their day indoors, where lighting is typically far dimmer than natural daylight. Researchers are examining whether these differences in everyday light exposure have implications for long-term brain health. Credit: Shutterstock

Researchers found that insufficient exposure to bright daytime light may be a stronger predictor of dementia than several established risk factors.

Greater exposure to bright light during the day may be associated with a lower risk of developing dementia, according to research involving nearly 88,000 adults. Participants whose average daytime light exposure exceeded 1,000 lux had a 16% lower dementia risk than those exposed to dimmer conditions.

The study, published in General Psychiatry, analyzed light exposure in 87,577 adults who wore wrist devices equipped with light sensors for seven days. Over a median follow-up of 8.1 years, 741 participants developed dementia. The association between brighter daytime light and lower dementia risk remained significant after researchers accounted for numerous health, lifestyle, and environmental factors.

How Much Daytime Light Is Associated With Lower Dementia Risk?

Both light intensity and exposure duration were associated with dementia risk. Participants who experienced at least 42 minutes of bright daytime light at 5,000 lux or higher had a 17% lower risk than those with less exposure. For comparison, 1,000 lux is roughly equivalent to the brightness of an overcast day outdoors, considerably brighter than typical indoor lighting.

In a separate analysis, receiving fewer than 42 minutes of bright daytime light ranked as a stronger predictor of dementia than six established risk factors, including obesity, alcohol consumption, and traumatic brain injury. By contrast, nighttime light exposure showed no statistically significant association with dementia risk.

Why Light Exposure May Matter for Brain Health

Daytime light helps regulate circadian rhythms, the body’s internal timing system that influences sleep, daily activity, and cognitive function. Additional analyses suggested that differences in these rhythms and certain brain structures might partly explain the relationship. The association was particularly pronounced among evening chronotypes, people carrying the APOE ε4 genetic variant, and those exposed to higher levels of nighttime light.

However, the observational findings do not establish that increasing daytime light exposure prevents dementia. Light exposure was measured for only one week, and wrist sensors cannot precisely capture the amount of light reaching the eyes. Further research is needed to determine whether changing light exposure can directly influence dementia risk.

“Daytime light exposure may serve as a novel indicator of dementia risk,” said corresponding author Hongliang Feng, PhD, of Guangzhou Medical University, in China.

Reference: “Associations between wearable-device-measured daytime and nighttime light exposures and dementia risk: A prospective cohort study” by Nana Zheng, Wei Wang, Biao Li, Xionge Mei, Yue Liu, Jing Du, Ngan Yin Chan, Joey W. Y. Chan, Xiaoman Xing, Xiao Tan, Christian Benedict, Yun Kwok Wing, Jihui Zhang and Hongliang Feng, 24 June 2026, General Psychiatry.
DOI: 10.1002/gps3.70039

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