Daylight lowered dementia risk for 87,000 adults

A study of 87,577 adults found that people who got more bright daylight during the day had a lower risk of developing dementia, with researchers pointing to one quietly alarming threshold. Getting less than 42 minutes of bright daytime light a day was a stronger predictor of dementia than six established risk factors. The participants wore wrist devices with accelerometers that measured their light exposure around the clock. Over a median follow-up of 8.1 years, 741 of them developed dementia. People exposed to average daytime light above 1,000 lux, roughly an overcast day outdoors, had a 16% lower risk, and longer stretches in brighter light lowered it further. Nighttime light showed no significant link. "Daytime light exposure may serve as a novel indicator of dementia risk," said corresponding author Hongliang Feng of Guangzhou Medical University. The study, published in General Psychiatry, cannot prove daylight prevents dementia. An overcast walk, it turns out, still counts.