Higher exposure to bright light during the day may be associated with a reduced risk of dementia, according to a study published in General Psychiatry. The research, which analyzed data from nearly 87,577 adults in the U.K., found that individuals with more significant daytime light exposure had a 16% lower risk of developing dementia compared to those with less exposure.
Researchers observed that spending less than 42 minutes per day in bright daylight, defined as at least 5,000 lux, was a better predictor of dementia risk than six established factors, including alcohol consumption, obesity, hearing loss, traumatic brain injury, air pollution, and vitamin D supplement use. The study's findings suggest that circadian regulation, influenced by bright daytime light, may play a role in maintaining stable sleep-wake rhythms and potentially protecting brain areas linked to dementia.
The study utilized wrist sensors worn by participants for one week to objectively measure light exposure during both day and night. Over a median follow-up period of 8.1 years, 741 participants developed dementia. Those whose average daytime light exposure exceeded 1,000 lux, roughly the brightness of an overcast day, showed a reduced dementia risk. Further reductions were observed with exposure to brighter light, at least 5,000 lux, for longer durations.
Interestingly, the association between daytime light and dementia risk was more pronounced in individuals with higher nighttime light exposure, those who identified as "night owls," and carriers of the APOE ε4 gene, a known genetic risk factor for Alzheimer's disease. In these groups, increased daytime light exposure was linked to dementia risk reductions ranging from approximately 19% to 41%.
While the study highlights a potential protective effect, researchers caution that it does not definitively prove that increased daytime light prevents dementia. The study participants were generally healthier and from more socioeconomically advantaged backgrounds than the general population, which may limit the generalizability of the findings. Additionally, the one-week monitoring period and data collection predating the widespread adoption of LED lighting and increased nighttime device use might influence the results. Further research is needed to confirm these findings and explore the full implications of light exposure on cognitive health. The study authors suggested that increasing daytime light exposure could be a simple and cost-free strategy to potentially reduce dementia risk in both clinical and community settings.