Bright light therapy and circadian rhythm regulation for delirium prevention in hospitalised adults: a systematic review and meta-analysis

OBJECTIVE: To evaluate the effects of bright light therapy (BLT) on circadian regulation and delirium incidence in hospitalised adults. DESIGN: Systematic review and meta-analysis. DATA SOURCES: Scopus, MEDLINE, EMBASE, CINAHL and PsycINFO were searched from database inception to October 2025. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Randomised controlled trials, controlled clinical trials and pilot studies evaluating BLT for delirium prevention in hospitalised adults published in English were included. DATA EXTRACTION AND SYNTHESIS: Risk of Bias was assessed using the Risk of Bias tool for randomised trials (version 2) or Risk Of Bias In Non-randomised Studies of Interventions. Publication bias was explored using visual inspection of funnel plots. Data were narratively synthesised to summarise BLT protocolisation, adherence and impact on circadian rhythm and delirium incidence. Random-effects meta-analysis was performed to estimate pooled risk ratios (RRs) for delirium incidence. Certainty of evidence was assessed using GRADE. RESULTS: Eight studies (participants n=1190) were included. Risk of bias for delirium incidence varied, with several studies judged to have some concerns or high risk of bias. Adherence, cessation and adverse events were inconsistently measured and reported across studies. Three studies assessed circadian outcomes: two reported increased circadian cycle lengths following BLT, while one found no between-group differences. Most studies applied morning BLT at intensities ≥5000 lux for 60-120 min over 3-4 days. Meta-analysis demonstrated an uncertain effect of BLT on delirium incidence (RR 0.64, 95% CI 0.38 to 1.07; p=0.09), with moderate heterogeneity (I²=52.06%). The certainty of evidence was very low because of risk of bias, inconsistency, imprecision and potential publication bias. CONCLUSIONS: Current evidence remains uncertain regarding the effect of BLT on delirium incidence in hospitalised adults. Further high-quality studies are needed to determine effectiveness, identify optimal intervention characteristics and clarify the role of sleep-related mechanisms in delirium prevention. PROSPERO REGISTRATION NUMBER: CRD42020193040.