Study: Less than 42 minutes of bright daylight a day linked to more dementia
A study of nearly 88,000 adults links little bright daylight to a higher risk of dementia. It does not establish cause and effect.
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People who get little bright light during the day are more likely to develop dementia, according to a large cohort study. A team led by Hongliang Feng of Guangzhou Medical University in China analysed data from 87,577 adults who wore wrist sensors that measured light exposure during the day and at night. Participants were followed for a median of 8.1 years, and 741 of them developed dementia. The study was published in the journal General Psychiatry, the science news service ScienceDaily reported on Oct. 29, 2026, citing the publisher Wiley.
When average daytime light was above 1,000 lux – roughly an overcast day outdoors, according to the release – the risk of dementia was 16% lower. More time in even brighter light of at least 5,000 lux was associated with a further reduction in risk. Less than 0.7 hours, or 42 minutes, of bright daylight per day was a stronger predictor of dementia than six established risk factors, the authors said. The researchers found no statistically significant link between light at night and dementia risk.
The findings show an association but do not establish that more daylight directly prevents dementia, the release said. "Daytime light exposure may serve as a novel indicator of dementia risk," Feng said. The summary does not name the six risk factors used for comparison. Anyone with questions about their own risk should consult a doctor.
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