Journal
AMERICAN JOURNAL OF EPIDEMIOLOGY
Volume 187, Issue 3, Pages 427-434Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/aje/kwx290
Keywords
circadian rhythm; depression; depressive symptoms; epidemiology; light at night
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Funding
- JSPS KAKENHI [25461393, 15H04777, 15H04776, 24790774, 25860447, 22790567]
- Sekisui Chemical Co., Ltd.
- EnviroLife Research Institute Co., Ltd.
- Tokyo Electric Power Company
- Ushio Inc.
- Daiwa Securities Health Foundation
- Mitsui Sumitomo InsuranceWelfare Foundation
- Japan Diabetes Foundation
- Japan Science and Technology Agency
- Nara Prefecture Health Promotion Foundation
- Department of Indoor Environmental Medicine, Nara Medical University
- Meiji Yasuda Life Foundation of Health and Welfare
- Osaka Gas Group Welfare Foundation
- YKK AP Inc.
- Nara Medical University
- Grants-in-Aid for Scientific Research [15H04777, 15H04776, 16K09478, 15K09356] Funding Source: KAKEN
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Previous studies have indicated that minimal exposure to light at night (LAN) increases depression risk, even at 5 lux, in nocturnal and diurnal mammals. Although such low-level LAN may affect human circadian physiology, the association between exposure to LAN and depressive symptoms remains uncertain. In the present study, bedroom light intensity was measured objectively, and depressive symptoms were assessed, during 2010-2014 in Nara, Japan. Of 863 participants (mean age = 71.5 years) who did not have depressive symptoms at baseline, 73 participants reported development of depressive symptoms during follow-up (median, 24 months). Compared with the dark group (average of < 5 lux; n = 710), the LAN group (average of a parts per thousand 5 lux; n = 153) exhibited a significantly higher depression risk (hazard ratio = 1.89; 95% CI: 1.13, 3.14), according to a Cox proportional hazards model adjusting for age, sex, body mass index, and economic status. Further, the significance remained in a multivariable model adjusting for hypertension, diabetes, and sleep parameters (hazard ratio = 1.72; 95% CI: 1.03, 2.89). Sensitivity analyses using bedroom light data with a cutoff value of a parts per thousand 10 lux suggested consistent results. In conclusion, these results indicated that exposure to LAN in home settings was independently associated with subsequent depression risk in an elderly general population.
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