Day and night light exposure measured by wearable devices linked to dementia risk

Over a median follow-up of 8.1 years, 741 participants developed dementia.

• Daytime light exposure above 1000 lux is associated with reduced dementia risk (hazard ratio 0.84).
• Longer exposure to bright light (≥ 0.70 hours at ≥ 5000 lux) further reduces dementia risk (hazard ratio 0.83).
• Circadian rest-activity rhythms and brain structures may mediate up to 33% of the association between light exposure and dementia risk.
• Stronger protective associations were observed in individuals with high nighttime light exposure, an evening chronotype, or ε4 carrier status, resulting in a risk reduction of up to 41%.
• Less than 0.70 hours per day of bright daytime light (≥ 5000 lux) was found to outperform six established dementia predictors.

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