Effects of Light Therapy on Mood and Sleep Disorders: A Systematic Review and Meta-analysis (Preprint)

<sec> <title>BACKGROUND</title> Light therapy (LT) had become a frequently-used treatment method for treating emotional disturbance and sleep disorders due to its convenience, safety and low cost. </sec> <sec> <title>OBJECTIVE</title> To synthesize the research progress regarding the connections among light, sleep and mood, as well as evaluate the influencing factors of LT on depression improvement and impact of LT on the functional connectivity between multiple brain structures. </sec> <sec> <title>METHODS</title> Relevant clinical trials were searched in 5 databases from January 1th 2020 to June 30th 2025. Quality of studies was assessed by Risk of Bias Tool 2 and GRADE. The primary outcome was depression improvement and secondary outcomes were anxiety improvement and sleep quality. The random effects model was applied, and heterogeneity was assessed by I2 statistics. Meta-regression analysis was conducted to explore possible influencing factors. Sensitivity analysis was used to evaluate robustness. </sec> <sec> <title>RESULTS</title> Depression improvement between two groups reached a significant level (SMD = 0.51, 95% CI [0.34, 0.68], p = 0.00, I2 = 24.96%). Anxiety was tended to be significantly improved (MD = 1.95, 95% CI [-0.03, 3.94], p=0.05). Sleep efficiency (MD = 4.65, 95% CI [1.19, 8.11], p = 0.01), PSQI scores (MD = 1.60, 95% CI [0.71, 2.50], p = 0.00) and ISI score (MD = 3.45, 95% CI [2.00, 4.89], p = 0.00) significantly changed. There was positive correlation between treatment duration and depression improvement (β = 0.09, p = 0.037). </sec> <sec> <title>CONCLUSIONS</title> LT had a positive effect on depression, anxiety and sleep. Treatment duration and depression improvement was positively correlated. </sec>