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Obayashi, K., Saeki, K., Iwamoto, J., Ikada, Y., & Kurumatani, N. (2014). Association between light exposure at night and nighttime blood pressure in the elderly independent of nocturnal urinary melatonin excretion. Chronobiol Int, 31(6), 779–786.
Abstract: Circadian misalignment between internal and environmental rhythms dysregulates blood pressure (BP) variability because of disruption of the biological clock, resulting in increased nighttime BP. Although exposure to light-at-night is associated with the circadian misalignment, it remains unclear whether exposure to light-at-night in home settings is associated with nighttime BP. In this cross-sectional analysis of 528 elderly individuals (mean age: 72.8 years), we measured bedroom light intensity at 1-min intervals on two consecutive nights along with ambulatory BP, overnight urinary melatonin excretion and actigraphy. With regard to adjusted mean comparisons using analysis of covariance, the light-at-night group (average: >/=5 lux; n = 109) showed significantly higher nighttime systolic BP (SBP; adjusted mean: 120.8 vs. 116.5 mmHg, p = 0.01) and diastolic BP (70.1 vs. 67.1 mmHg, p < 0.01) compared with the Darker group (average: <5 lux; n = 419) independently of potential confounding factors including overnight urinary melatonin excretion and actigraphic sleep quality. We observed consistent associations between light-at-night and nighttime BP in different cutoff values for light-at-night intensity (i.e. 3 and 10 lux). In conclusion, exposure to light-at-night in home settings is significantly associated with increased nighttime BP in elderly individuals independently of overnight urinary melatonin excretion. A 4.3 mmHg increase in nighttime SBP is associated with a 6.1% increase in total mortality, which corresponds to approximately 10 000 annual excess deaths in Japanese elderly population.
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Obayashi, K., Saeki, K., & Kurumatani, N. (2018). Bedroom Light Exposure at Night and the Incidence of Depressive Symptoms: A Longitudinal Study of the HEIJO-KYO Cohort. Am J Epidemiol, 187(3), 427–434.
Abstract: 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 >/=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 >/=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.
Keywords: Human Health; Mental Health; indoor light; geriatrics; Sleep; Sleep Disorders
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Obayashi, K., Yamagami, Y., Kurumatani, N., & Saeki, K. (2019). Bedroom lighting environment and incident diabetes mellitus: a longitudinal study of the HEIJO-KYO cohort. Sleep Medicine, 65, 1–3.
Abstract: Objectives
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. We hypothesized that LAN exposure increases the diabetes risk in humans. The aim of the present study was to evaluate a longitudinal association between LAN exposure and the incidence of diabetes in a general population. Methods In our prospective cohort study, bedroom light intensity was measured at 1-min intervals in 678 elderly participants without diabetes at baseline. The average light intensity recorded between bedtimes and rise times over two consecutive nights was used in the analysis. Results During follow-up (median, 42 months), 19 of the 678 participants (mean age, 70.6 years) developed diabetes. Poisson regression models revealed that the incidence rate for diabetes was significantly higher in the LAN group (average ≥5 lux, N = 128) than the dark group (average <5 lux, N = 550) (incidence rate ratio, 3.74; 95% confidence interval (CI), 1.55–9.05; p=0.003). Further propensity score adjustments in relation to LAN produced consistent results (incidence rate ratio, 3.19; 95% CI, 1.38–7.35; p=0.007). When the cut-off value of LAN was decreased to 3 lux, the relationship remained significant (incidence rate ratio 2.74; 95% CI, 1.19–6.33; p=0.018). Conclusions Our findings suggest that LAN exposure increases the incidence of diabetes in a general elderly population. Further research involving a large cohort with new-onset diabetes is warranted to elucidate these findings. Keywords: Human Health; Metabolic disorders; diabetes; geriatrics
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