August 26, 2026
As the days grow shorter, don’t forget to spend some time outdoors. Exposure to outdoor light may be good for the health of the brain, according to a new report. The study, published in General Psychiatry, found that older adults who got more exposure to bright daylight were less likely to develop Alzheimer’s disease and other forms of dementia down the road.
For the study, researchers at Guangzhou Medical University in China analyzed data from 87,577 men and women who were part of the U.K. Biobank, a long-running study of aging and health in Britain. Their average age was 62 at the start of the study period, and none had dementia or serious memory problems.
Participants wore a wrist device equipped with a light sensor over a period of seven days. The device measured their movement as well as typical exposure to daytime and nighttime light levels. Light exposure was measured in a unit called lux. Indoor light is typically around 300 to 500 lux, while the outdoor light level on an overcast day is about 1,000 lux. A bright sunny day can far exceed levels of 5,000 lux.
Researchers followed them for a little more than eight years on average. During that time, more than 700 developed Alzheimer’s disease or another form of dementia.
Analysis revealed that greater exposure to daytime light was associated with a lower risk of developing dementia. People whose average daytime light exposure was greater than 1,000 lux had a 16 percent lower risk of dementia than those getting less daytime light exposure. Those who were exposed to at least 40 minutes a day of light of at least 5,000 lux had a 17 percent lower dementia risk.
The link appeared strongest in those who may have had an increased dementia risk, including those who carried the APOE-E4 gene variant and night owls, who tend to stay up late into the night. The researchers noted that exposure to daytime light may be particularly beneficial for these groups.
The researchers also found that getting less than about 40 minutes of bright daytime light of at least 5,000 lux was a stronger predictor of dementia than various other known dementia risk factors, including heavy alcohol use, exposure to high levels of air pollution, hearing loss or being obese.
The study showed only an association between daytime light exposure and dementia risk and cannot prove cause and effect. But daytime light is known to affect the body’s circadian rhythms and help to balance natural sleep-wake cycles. Poor or disrupted sleep is a well-recognized risk factor for Alzheimer’s disease. Exposure to sunlight can also boost natural production of vitamin D, also known as the “sunshine vitamin.” Low vitamin D levels are tied to an increased risk of dementia.
In this study, nighttime light exposure did not seem to affect dementia risk. Other research, however, shows that heavy exposure to nighttime lights or bedtime exposure to electronic devices like computer or tablet screens and televisions may impair sleep and raise dementia risk.
The findings suggest that getting outside for at least part of the day may be an easy way to help keep the brain in good working order. Go for a morning walk, or have lunch outdoors when you can. For those who can’t get outside, even sitting near a sunlit window may provide high levels of light exposure.
Daytime light exposure may also have benefits for those with Alzheimer’s disease. Studies suggest, for example, that exposure to bright light may help to improve thinking and memory skills and ease agitation in people with dementia. If you’re caring for someone with Alzheimer’s, take them out during the day for a walk, allow them to sit outdoors in the sunlight, or try to bring more natural sunlight into rooms indoors. It may have lasting benefits for both of you.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, PhD, of The Fisher Center lab at The Rockefeller University.
Source: Nana Zheng, Wei Wang, Biao Li, et al: “Associations between wearable-device-measured daytime and nighttime light exposures and dementia risk: A prospective cohort study.” General Psychiatry, June 24, 2026
