Brief CommunicationBedroom lighting environment and incident diabetes mellitus: a longitudinal study of the HEIJO-KYO cohort
Introduction
The circadian timing system, located within the suprachiasmatic nucleus of the hypothalamus, controls fundamental energy homeostasis. Clock gene mutations induce obesity in mice, and the disruption of internal circadian rhythms decreases daily energy expenditures and leptin levels in humans [1], [2], [3]. Light information received by the brain influences human circadian timing and metabolism; low-level light at night (LAN) significantly increased body mass and led to prediabetes in mice [4], [5], [6]. In humans, bedroom LAN affected obesity parameters; however, the association between LAN and the incidence of diabetes in humans has not been studied [7], [8].
Section snippets
Participants and study protocol
Data on the HEIJO-KYO cohort, focusing the housing environments and health outcomes among 1127 community-dwelling elderly individuals aged ≥60 years, were analyzed. This study protocol has been reported previously [9]. In brief, we measured baseline LAN exposure and diabetic status between September and April 2010–2014 and followed-up diabetic status between January 2016 and March 2017. All participants provided written informed consent. The study protocol was approved by the Nara Medical
Results
Overall, 154 of the 1108 participants who completed LAN measurements and the diabetes survey at baseline had diabetes and were therefore excluded. Of the remaining participants, 678 (71.1%; mean age, 70.6 ± 6.6 years; 44.5% were males) participated in a follow-up assessment and completed the diabetes survey. Compared with the dark group (avg < 5 lux, N = 550) at baseline, the LAN group (avg ≥ 5 lux, N = 128) had a significantly earlier average bedtime (mean, 22:37 h; range, 19:27–03:53 h) and
Discussion
Bedroom LAN and the incidence of diabetes were independently associated in a general elderly population. To our knowledge, this study is the first to demonstrate that LAN exposure in home settings increases the incidence of diabetes in humans. Our results support the epidemiological evidence that night-shift works increase LAN, thereby leading to circadian misalignment and an increased risk of diabetes [11], [12]. The longitudinal design, use of objective measurement of bedroom LAN, and
Acknowledgments
The authors would like to thank Naomi Takenaka, Sachiko Sogahara, Keiko Nakajima, and Megumi Natsuaki for their valuable help with data collection and analysis. This work was supported by research funding from the Department of Indoor Environmental Medicine, Nara Medical University; JSPS KAKENHI (grant numbers: 24790774, 22790567, 25860447, 25461393, 15H04776, and 10124877); Mitsui Sumitomo Insurance Welfare Foundation; Meiji Yasuda Life Foundation of Health and Welfare; Osaka Gas Group Welfare
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