P105 Healthy light exposure enhances SSRI efficacy in depression: case study

Abstract Background Depression is the leading cause of non-fatal disease burden worldwide, with disturbances in the circadian system commonly observed in affected individuals. Selective serotonin reuptake inhibitors (SSRIs), a first-line treatment for depression, significantly enhance the circadian system’s sensitivity to light. The benefits of this increased sensitivity may depend on the balance between beneficial daytime light exposure and adverse night-time brightness. Method This case study explored whether variability in healthy light exposure patterns - more daytime light and less night-time light - related to SSRI treatment efficacy. A 27-year-old female patient experiencing depression underwent an 8-week intervention with citalopram, the most commonly prescribed SSRI. Light exposure was monitored using a custom wearable spectrophotometer, which continuously recorded exposure to light across the entire visible spectrum. Mood was assessed fortnightly using the Montgomery-Asberg Depression Rating Scale (MADRS). Results At baseline, the patient had a MADRS score of 29, indicating moderate depression (range: 20-34). During the intervention, healthier light exposure patterns - brighter daytime light and minimal light at night - aligned with improved mood over this period. By the final assessment, their MADRS score had decreased to a level consistent with mild depression (range: 7-19). Discussion Healthy light exposure patterns are known to strengthen circadian rhythms. Our findings highlight the potential for promoting healthier light exposure to optimise antidepressant treatment efficacy and improve treatment outcomes in depression.