HealthDay News — High levels of daytime light exposure are associated with a lower risk for dementia, according to a study based on U.S. data published online June 24 in General Psychiatry. Nana Zheng, Ph.D., from The Affiliated Brain Hospital, Guangzhou Medical University in China, and colleagues examined the associations of daytime and nighttime light exposure with dementia risk in a study involving 87,577 dementia-free participants. Seven-day free-living wrist-worn accelerometry was used to measure daytime and nighttime light exposures.

Overall, 741 participants developed dementia during a median follow-up of 8.1 years. The researchers found that dementia risk was reduced in association with daytime light exposure above 1,000 lux (hazard ratio, 0.84). Further reduction in risk was seen in association with longer exposure to brighter light (e.g., ≥0.70 hour at ≥5,000 lux: hazard ratio, 0.83). Up to 33 percent of the association was mediated by circadian rest-activity rhythms and brain structures. Stronger protective associations were seen in those with high levels of nighttime light exposure, an evening chronotype, or APOE ɛ4 carrier status, with up to a 41 percent risk reduction. Six established dementia predictors were outperformed by <0.70 hours per day of bright daytime light (≥5,000 lux). No significant association was seen for nighttime light with dementia risk. “These findings suggest a targeted approach to mitigate dementia risk by increasing daytime light levels for these populations,” the authors write.

One author disclosed ties to Lundbeck.