Researchers analyzing data from 87,577 adults found that exposure to brighter daytime light was associated with lower dementia risk. The study, published in General Psychiatry, tracked participants wearing wrist devices with accelerometers that measured light exposure over a median of 8.1 years. During that period, 741 participants developed dementia.
People exposed to average daytime light levels exceeding 1,000 lux had a 16% lower dementia risk. Exposure to even brighter light, at least 5,000 lux, was linked to further risk reductions.
The most striking finding involved minimal bright light exposure. Getting less than 42 minutes of bright daytime light daily was a stronger predictor of dementia than six established dementia risk factors, according to the researchers.
Nighttime light exposure showed no statistically significant connection to dementia risk, suggesting that daytime brightness matters more than nighttime light.
"Daytime light exposure may serve as a novel indicator of dementia risk," said Hongliang Feng, PhD, of Guangzhou Medical University, the corresponding author.
The researchers caution that the findings reveal an association only. The study does not establish that increased daylight directly prevents dementia. Instead, the work identifies daytime light exposure as a potentially valuable risk indicator warranting further investigation.