Daytime and nighttime light exposures and dementia risk

A UK Biobank study examined the associations of daytime and nighttime light exposure with dementia risk (1):

• community-based cohort study was based on the UK Biobank, a large population-based cohort that enrolled over 500,000 participants aged 40–73 years between 2006 and 2010
• total of 87,577 dementia-free participants (mean age: 62.36 years; 56.98% female) were included
• daytime and nighttime light exposures were measured using 7-day free-living wrist-worn accelerometry. Incident dementia was identified from primary care, hospital inpatient admissions and death registry data
  • Cox proportional hazards models assessed associations, and mediation analyses evaluated circadian rest–activity rhythms (CRARs), brain structures and vitamin D as potential mediators

Study results:

• over a median follow-up of 8.1 years, 741 participants developed dementia.
  • daytime light exposure above 1000 lux was associated with reduced dementia risk (hazard ratio [HR] 0.84, 95% confidence interval [CI] 0.71–0.99, p = 0.039)
    • longer exposure to brighter light (e.g., ≥ 0.70 h at ≥ 5000 lux; HR 0.83, p = 0.036) was associated with a further reduction in risk. In exploratory analyses, CRARs and brain structures mediated up to 33% of the association
    • protective associations were stronger in those with high levels of nighttime light exposure, an evening chronotype or apolipoprotein E (APOE) ε4 carrier status, with a risk reduction of up to 41%
    • < 0.70 h per day of bright daytime light (≥ 5000 lux) outperformed six established dementia predictors (e.g., obesity, alcohol consumption, traumatic brain injury and so on)
    • nighttime light showed no significant association with dementia risk

Conclusion

• high levels of daytime light exposure were significantly associated with lower dementia risk

The study authors have suggested implications based on this research:

1. the importance of higher daytime light exposure in reducing dementia risk, which appears to exceed many traditional predictors
2. increasing daytime light exposure may be a simple and cost-free strategy to reduce dementia risk in both clinical and community settings
3. findings underscore a more pronounced protective association of daytime light exposure in individuals with higher average nighttime light exposure, an evening chronotype or APOE ε4 carrier status

Reference:

1. Zheng, N, et al. (2026). Associations between wearable-device-measured daytime and nighttime light exposures and dementia risk: A prospective cohort study. Gen Psychiatr, 39(3):e70039.