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Tsujimoto, T., Yamada, N., Shimoda, K., Hanada, K., & Takahashi, S. (1990). Circadian rhythms in depression. Journal of Affective Disorders, 18(3), 199–210.
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Min, J. -young, & Min, K. -bok. (2018). Outdoor light at night and the prevalence of depressive symptoms and suicidal behaviors: a cross-sectional study in a nationally representative sample of Korean adults. Journal of Affective Disorders, 227, 199–205.
Abstract: Background
Outdoor light at night (LAN) is an increasingly prevalent type of environmental pollution. Studies have demonstrated that outdoor LAN can disrupt circadian rhythms, potentially contributing to insomnia, cancer, cardiovascular disease, and metabolic changes in humans. We investigated the association of outdoor LAN with depressive symptoms and suicidal behaviors in South Korean adults.
Methods
This study used data from the 2009 Korean Community Health Survey, a representative sample dataset. Study population consisted of 113,119 participants for the assessment of depressive symptoms and 152,159 participants for the assessment of suicidal behavior. Depressive symptoms were measured using the Korean version of the Center for Epidemiologic Studies Depression Scale (depressive symptoms, score of > 16). Suicidal behaviors were defined as the experience of suicidal ideation or attempt. Outdoor LAN was estimated by satellite data from the National Centers for Environmental Information.
Results
Participants with depressive symptoms or history of suicidal behaviors were more likely to have exposure to outdoor LAN than those without depressive symptoms or suicidal behaviors. Compared with adults living in areas exposed to the lowest outdoor LAN, those living in areas exposed to the highest levels had higher likelihood depressive symptoms (OR = 1.29; 95% CI: 1.15–1.46) or suicidal behaviors (OR = 1.27; 95% CI: 1.16–1.39). Significant dose-response relationships were observed between outdoor LAN and the odds of depressive symptoms and suicidal behaviors.
Conclusion
Outdoor LAN was found to be significantly associated with depressive symptoms and suicidal behaviors, suggesting that it may be an environmental contributor to mental health problems.
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Esaki, Y., Kitajima, T., Obayashi, K., Saeki, K., Fujita, K., & Iwata, N. (2019). Light exposure at night and sleep quality in bipolar disorder: the APPLE cohort study. Journal of Affective Disorders, in press.
Abstract: Background
Sleep disturbance in bipolar disorder (BD) is common and is associated with a risk for mood episode recurrence. Thus, it is important to identify factors that are related to sleep disturbance in BD. This cross-sectional study investigated the association between exposure to light at night (LAN) and sleep parameters in patients with BD.
Methods
The sleep parameters of 175 outpatients with BD were recorded using actigraphy at their homes for seven consecutive nights and were evaluated using the Insomnia Severity Index (ISI). The average LAN intensity in the bedroom during bedtime and rising time was measured using a portable photometer, and the participants were divided into two groups: “Light” (≥5 lux) and “Dark” (<5 lux). The association between LAN and sleep parameters was tested with multivariable analysis by adjusting for potential confounder such as age, gender, current smoker, mood state, day length, daytime light exposure, and sedative medications.
Results
After adjusting for potential confounder, the actigraphy sleep parameters showed significantly lower sleep efficiency (mean, 80.1% vs. 83.4%; p = 0.01), longer log-transformed sleep onset latency (2.9 vs. 2.6 min; p = 0.01), and greater wake after sleep onset (51.4 vs. 41.6 min; p = 0.02) in the Light group than in the Dark group. Whereas, there were no significant differences in the ISI scores between the groups.
Limitations
This was a cross-sectional study; therefore, the results do not necessarily imply that LAN causes sleep disturbance.
Conclusions
Reducing LAN exposure may contribute to improved sleep quality in patients with BD.
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