Effects of bright light therapy on cognition, sleep and psychological stress in older adults with mild-to-moderate cognitive impairment: a pilot study in long-term care facilities

This study aimed to investigate the effects of morning bright light therapy (BLT) on cognitive function, sleep and psychological stress levels in older adults with mild-to-moderate cognitive impairment (MMCI) residing in long-term care facilities in China. Twenty older adults with MMCI completed a 35-day trial, the initial 7-day adaptation period was classified as pre-BLT. Subsequently, participants received daily 60-minute BLT sessions at 10,000 lx starting at 9:00 AM. The intervention period was divided into three phases: post-BLT1 (9-day), post-BLT2 (9-day) and post-BLT3 (10-day). Cognitive function was evaluated using the Chinese Mini-Mental State Examination (MMSE). Sleep parameters were measured objectively using the non-wearable mattress-type sleep monitor and psychological stress was assessed via salivary chromogranin A (CgA). Statistical analyses were conducted across these four phases using repeated-measures ANOVA and paired t-tests. MMSE scores increased significantly from pre to post-intervention (Δ = +0.85; p = 0.002). Total sleep time and deep sleep time were significantly higher at post-BLT2 and post-BLT3 compared to pre-BLT (p < 0.05). Body movement frequency was significantly lower at all post-BLT assessments (p < 0.05). Salivary CgA levels exhibited small, non-significant changes at the end of the intervention (p = 0.085). Following a 28-day BLT intervention, participants with MMCI showed a modest increase in MMSE scores and increases in total sleep time and deep sleep time, along with reduced body movement frequency. No significant change in salivary CgA levels was observed. These preliminary findings suggest that BLT may hold promise as a non-pharmacological approach to support sleep and cognitive health in long-term care settings.