Association between light exposure at night and manic symptoms in bipolar disorder: cross-sectional analysis of the APPLE cohort

ABSTRACT

Previous studies have found that keeping the room dark at night was associated with a decrease in manic symptoms for patients with bipolar disorder (BD). However, the association between light at night of real-life conditions and manic symptoms is unclear. We investigated the association between bedroom light exposure at night and manic symptoms in BD patients. One-hundred and eighty-four outpatients with BD participated in this cross-sectional study. The average light intensity at night during sleep was evaluated using a portable photometer for seven consecutive nights. Manic symptoms were assessed using the Young Mania Rating Scale (YMRS), and scores ≥5 were treated as a “hypomanic state.” The median (interquartile range) YMRS score was 2.0 (0–5.0), and 52 (28.2%) participants were in a hypomanic state. The prevalence of a hypomanic state was significantly higher in the participants with an average light intensity at night exposure of ≥3 lux than in those with <3 lux (36.7% versus 21.9%; P = .02). In multivariable logistic regression analysis adjusted for BD type, depressive symptoms, sleep duration, and daytime physical activity, the odds ratio (OR) for a hypomanic state was significantly higher for the participants with an average light intensity at night exposure of ≥3 lux than for those with <3 lux (OR: 2.15, 95% confidence interval: 1.09–4.22, P = .02). This association remained significant at the cutoff value of YMRS score ≥6 (OR: 2.51, 95% confidence interval: 1.15–5.46; P = .02). The findings of this study indicate bedroom light exposure at night is significantly associated with manic symptoms in BD patients. Although the results of this cross-sectional investigation do not necessarily imply causality, they may serve to inform beneficial nonpharmacological intervention and personalized treatment of BD patients.

KEYWORDS:

• Bipolar disorder
• manic symptom
• light at night
• dark
• circadian rhythm

Acknowledgements

We are grateful to the patients who participated in this study. We also thank Soji Tsuboi and Miyuki Yamamoto for their valuable support during this research.

Declaration of Interest statement

The authors report no conflicts of interest related to this research. Dr Obayashi and Dr Saeki has received a research grant from YKK AP Inc.; Ushio Inc.; Tokyo Electric Power Company; EnviroLife Research Institute Co., Ltd.; Sekisui Chemical Co., Ltd; LIXIL Corp.; and KYOCERA Corp. Dr Fujita has received speaker’s honoraria from Dainippon Sumitomo, Eli Lilly, GlaxoSmithKline, Janssen, Yoshitomi, Otsuka, Meiji, Shionogi, Novartis, and Kracie. Dr Iwata has received speaker’s honoraria from Astellas, Dainippon Sumitomo, Eli Lilly, GlaxoSmithKline, Janssen, Yoshitomi, Otsuka, Meiji, Shionogi, Novartis, and Pfizer and has had research grants from GlaxoSmithKline, Meiji, Otsuka, Mitsubishi Tanabe, Dainippon Sumitomo, Daiichisankyo, and Eisai. Dr Kitajima has received speaker’s honoraria from Eisai, Mitsubishi Tanabe, Otsuka, Takeda, Eli Lilly, MSD, Meiji, Yoshitomi, Fukuda, Dainippon Sumitomo, Shionogi, and Novo Nordisk, and has received a research grant from Eisai, MSD and Takeda.

Supplementary Material

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Additional information

Funding

This work was supported by the Japan Foundation for Neuroscience and Mental Health; The Neuroscience Research Center; Scientific Research from JSPS KAKENHI [18K15529].