Preventive effect of morning light exposure on relapse into depressive episode in bipolar disorder
Yuichi Esaki, Kenji Obayashi, Keigo Saeki, Kiyoshi Fujita, Nakao Iwata, Tsuyoshi Kitajima
Abstract
OBJECTIVE: Light therapy has been suggested to have a curative effect on bipolar depression; however, preventive effects of light exposure on depressive episodes remain unclear. This study evaluated whether daytime light exposure in real-life situations was associated with a preventive effect on relapse into depressive episodes in patients with bipolar disorder. METHODS: This prospective, naturalistic, observational study was conducted in Japan between August 2017 and June 2020. Outpatients with bipolar disorder were objectively evaluated for daytime light exposure over 7 consecutive days using an actigraph that could measure ambient light at baseline assessment and then assessed at 12-month follow-up for relapse into mood episodes. RESULTS: Of 202 participants, 198 (98%) completed follow-up at 12 months and 78 (38%) experienced relapse into depressive episodes during follow-up. In a Cox proportional hazards model adjusting for potential confounders, a longer time above 1000 lux at daytime was significantly associated with decrease in relapse into depressive episodes (per log min; hazard ratio, 0.66; 95% confidence interval, 0.50-0.91). In addition, a higher average illuminance and longer time above 1000 lux in the morning exhibited a significant decrease in relapse into depressive episodes (per log lux and per log min; hazard ratio, 0.65 and 0.61; 95% confidence interval, 0.49-0.86 and 0.47-0.78, respectively). The association between daytime light exposure and relapse into manic/hypomanic/mixed episodes was not significantly different. CONCLUSION: A significant association was observed between increased daytime light exposure, mainly in the morning, and decreased relapse into depressive episodes.