Kenji Obayashi

Kenji Obayashi
Nara Medical University

M.D., Ph.D.
Department of Epidemiology, Nara Medical University School of Medicine

About

104
Publications
9,566
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1,559
Citations
Citations since 2016
67 Research Items
1359 Citations
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
Introduction
Dr. Obayashi earned his M.D. at Tokyo Medical University, and Ph.D. at Nara Medical University, Japan. He completed post-graduate training in Internal Medicine and clinical fellowship in Adult Cardiology from Tokyo Women’s Medical University, Japan. He is Board Certified in Internal medicine and Cardiology. Currently, Dr. Obayashi’s special interests include Epidemiology related to Circadian Rhythm (Chronoepidemiology).
Additional affiliations
July 2012 - present
Nara Medical University
Position
  • Nara Medical University School of Medicine

Publications

Publications (104)
Article
Context: Previous epidemiological studies have suggested an association between nighttime light levels and the prevalence of obesity, although evidence is limited to cross-sectional studies. Objective: To evaluate the longitudinal association between ambient light exposure and the subsequent changes in obesity parameters. Design and partcipants...
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Previous studies have indicated that minimal exposure to light-at-night increases depression risk, even at 5 lux, in nocturnal and diurnal mammals. Although such low level light-at-night may be effective for human circadian physiology, the association between exposure to light-at-night and depressive symptoms remains uncertain. Bedroom light intens...
Article
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 betwe...
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Exposure to light at inappropriate times in relation to the solar cycle can disturb circadian endocrine and metabolic rhythms. Previous studies have suggested an association between light exposure at night (LAN) and obesity, an important risk factor of atherosclerosis, although it remains unclear whether LAN associates with progression of atheroscl...
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Nighttime use of artificial light is usual and essential in these modern times. Although light exposure at night (LAN) is reportedly a risk factor of several diseases, epidemiological studies on indoor LAN levels are still limited. Hence, the present study aimed to measure bedroom LAN levels by using light meters in a larger sample than in previous...
Article
Previous studies outlined the correlation of adverse effects of breakfast skipping with cognitive function. However, the majority of these studies have focused on the short-term effects; to date, the long-term effect of breakfast skipping on cognitive function among older adults remains unclear. In this prospective cohort study of 712 older adults...
Article
Objectives: Cold exposure accounts for more than 7% of all-cause mortality worldwide, and cold-induced blood pressure (BP) elevation and consequent cardiovascular events are partially responsible. For prevention, it is important to identify risk factors for exaggerated temperature-sensitivity of BP but this is not fully understood. This study inve...
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Background: The inverse association between ambient temperature and blood pressure (BP) has been investigated in the context of excess cardiovascular mortality in winter. However, the role of skin temperature (ST), which reflects our external and internal thermal environments, in BP regulation remains unclear. Therefore, we examined the associatio...
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Purpose: This study determines whether the functional and structural severity of glaucoma is associated with intrinsically photosensitive retinal ganglion cell (ipRGC) function. Methods: This cross-sectional study assessed 148 eyes from 148 patients with glaucoma (mean age 70.5 years). The ipRGC function was assessed by postillumination pupil re...
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Objective: A previous cross-sectional study reported that nighttime light is associated with increased occurrence of manic symptoms in bipolar disorder; however, the longitudinal association between nighttime light and subsequent mood episode relapses remains unclear. We determined whether bedroom nighttime light was associated with mood episode r...
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Objectives This study aimed to 1) determine what kind of care for children with disabilities is related to the mothers' sleep and mental well-being and 2) objectively measure the sleep state of mothers responsible for children with disabilities.Methods A self-administered questionnaire was distributed to 180 mothers of children enrolled in the Spec...
Article
Background: Cold exposure induces lower urinary tract symptoms, including nocturia. Cold-induced detrusor overactivity can be alleviated by increasing skin temperature in rats. However, no study has shown an association between passive heating via hot-water bathing and nocturia among humans. Methods: We included 1,051 Japanese community-dwelling ol...
Article
Objectives To determine the association between short-wavelength light exposure at night (LAN) power and sleep quality or melatonin levels in real-life settings. Methods In this cross-sectional study of 580 older adults (mean age, 71.0 years), we measured short-wavelength LAN power at cornea level using an originally developed light loggers over t...
Article
Background Sleep disturbance is a core feature of bipolar disorder; hence, sleep must be accurately assessed in patients with bipolar disorder. Subjective sleep assessment tools such as sleep diary and questionnaires are often used clinically for assessing sleep in these patients. However, the insight into whether these tools are as accurate as obj...
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A significant proportion of patients with bipolar disorder experience mood episode relapses. We examined whether circadian activity rhythms were associated with mood episode relapses in patients with bipolar disorder. This prospective cohort study included outpatients with bipolar disorder who participated in a study titled “Association between the...
Article
Precis: This cross-sectional study of 172 patients with glaucoma showed that functional and structural glaucoma damage was significantly associated with cognitive impairment independent of age and visual acuity. Purpose: The aim of this study was to determine whether functional and structural glaucoma damage is associated with cognitive function...
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Objectives Passive body heating can have an antidepressant effect by activating warm-sensitive neural pathways associated with affective functions. Interventional studies showed that patients with depression had reduced depressive symptoms after passive body heating. However, the effect of hot water bathing at home on depressive symptoms in the gen...
Article
Objective Circadian disruptions in Parkinson’s disease (PD) are characterized as amplitude reduction rather than as phase shift; however, large-scale studies evaluating circadian rhythms between PD patients and non-PD older adults have not been performed. The present study aimed to compare the circadian activity rhythm (CAR) between PD patients and...
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Purpose: Asymmetric dimethylarginine (ADMA), a potent endogenous inhibitor of nitric oxide synthase, may be involved in the pathophysiology of glaucoma by dysfunctioning nitric oxide and oxidative stress. The purpose of this study was to determine whether the serum ADMA level is associated with the severity of glaucoma. Methods: One hundred twen...
Article
Study objectives: Passive body heating in controlled settings could shorten sleep onset latency (SOL). The hypothesized mechanism is vasodilation-induced heat loss before bedtime. However, this evidence is based on small sample size studies in specific populations. Thus, we analyzed the association of hot water bathing based on before-bedtime timi...
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Objective Light therapy has been suggested to have a curative effect on bipolar depression; however, preventive effects of light exposure on depressive episodes remain unclear. This study evaluated whether daytime light exposure in real‐life situations was associated with a preventive effect on relapse into depressive episodes in patients with bipo...
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Obesity and overweight are highly prevalent in individuals with bipolar disorder and are associated with a risk of developing not only physical but also mental problems. The current study aimed to determine the association between bedroom light exposure at night and obesity in individuals with bipolar disorder. This cross-sectional study enrolled 2...
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Objective: Sleep disturbance, a core feature of bipolar disorder, is associated with residual mood symptoms, mood episode recurrence and suicide ideation. We investigated the effect of evening light exposure on sleep in patients with bipolar disorder. Methods: In this longitudinal analysis, we measured the sleep parameters of 207 outpatients with...
Article
Aims To investigate the association between B‐type natriuretic peptide (BNP) and nocturia among community‐dwelling males and females. Methods A total of 1096 participants (mean age 71.9 ± 7.1 years, 518 [47.2%] males) were included in the study. The number of nocturnal voids was recorded in a self‐reported urination diary, and nocturia was defined...
Article
Purpose: To assess skin perfusion pressure (SPP) changes after endovascular treatment (EVT) of patients with chronic limb-threatening ischemia (CLTI) and to explore preoperative factors that affect SPP changes. Materials and methods: This prospective, multicenter study recruited 147 patients (mean age 74 years; 99 men) with ischemic wounds at 6...
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Background: Previous studies have reported that estimates of portion size, energy, and macronutrients such as carbohydrates, proteins, and fat based on the food-photographic record closely correlate with directly weighed values. However, the correlation based on a large sample of the test meal with the evidence of many nutrients is yet to be deter...
Article
Background Patients with bipolar disorder (BD) frequently self-harm, and this is strongly associated with subsequent suicide. This study investigated the association between chronotype and intentional self-harm in patients with BD. Methods Two-hundred and five outpatients with BD participated in this cross-sectional study. Each participant's chron...
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Objective Melatonin is involved in the regulation of sleep and circadian biological rhythmicity; decreased melatonin secretion has been associated with circadian disruptions. Previous studies evaluating melatonin levels between patients with Parkinson's disease (PD) and controls without PD have found conflicting results; however, large-scale studie...
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Background There is a paucity of studies on self-assessed generic health-related quality of life (HRQOL) in children with epilepsy. The purpose of this study was to investigate generic HRQOL and associated factors among Japanese children with epilepsy. Methods In this clinic-based study, 277 children (aged 8–18 years) with epilepsy and 429 childre...
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Glaucoma may be associated with circadian disruption due to its association with a loss of intrinsically photosensitive retinal ganglion cells. Clinical evidence demonstrating an association between glaucoma and circadian disruption is limited, and no large‐scale studies have been performed. The purpose of this cross‐sectional study was to determin...
Article
The commentary by Dr. Smolensky provides an insightful assessment of our study from the circadian point of view. In the present letter, we have responded to the commentary by Dr. Smolensky et al., suggesting interpretation of our analytic results and providing additional statistical data regarding the timing of antihypertensive drug use. In additio...
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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...
Article
Importance Cataract surgery, which increases perception of light, may increase melatonin secretion. Melatonin secretion has been associated with depression, diabetes, cognitive impairment, and breast cancer. To date, no evidence from a randomized clinical trial exists to support this cataract surgery hypothesis. Objective To determine whether cata...
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Introduction: Assessing health-related quality of life (HRQOL) is critical for providing comprehensive clinical care to patients with haemophilia. HRQOL in individuals with similar cultural backgrounds should be compared using internationally standardized, generic questionnaires. Aim: To evaluate self-/parent-assessed HRQOL in Japanese children...
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First, we describe the importance of indoor thermal environment in terms of prevention from cardiovascular diseases based on the seasonal change of mortality, and the estimated burden of cold and heat-related mortality estimated by recently developed distributed lag nonlinear model. Second, we discuss the critical factors associated with the contro...
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Background: Maintenance of instrumental activities of daily living (IADL) and social role (SR) is crucial to keep independent life because the decline in SR and IADL was a significant predictor of dependence in basic ADL in later. The independent effect of physical and cultural leisure activities and their effect modification on the IADL remains u...
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Objectives: Prognostically, night-time blood pressure (BP) is more important than other BP parameters. Previous physiological studies suggested physical exercise continuously decreases subsequent BP levels, although the association between daytime physical activity and night-time BP has not been evaluated in large populations. Methods: This cros...
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Hot water bathing – a Japanese traditional practice – has not been evaluated for its association with night- and sleep-time blood pressure (BP) in large population. In this longitudinal analysis, bathing parameters and ambulatory BP were repeatedly measured for 2 nights in 758 Japanese elderly individuals. Participants were divided into three group...
Article
Objectives: Previous studies comparing objective sleep measures between patients with Parkinson's disease (PD) and control participants were limited by their small sample size. The purpose of this study was to compare objective sleep measures between large-scale cohorts of PD outpatients and community-based older adults. Methods: In this cross-s...
Article
Study objectives: Previous studies have suggested associations between sleep measures and early-morning akinesia; however, objective evidence is limited. The purpose of this study was to evaluate the associations between objective sleep measures and morning mobility among patients with Parkinson's disease (PD). Methods: In this cross-sectional s...
Article
Objectives: Comparing the incidence rate of in-hospital falls between patients hospitalized in window beds and nonwindow beds. Design: Retrospective cohort study. Setting: A general hospital in Mie, Japan. Participants: A total of 2767 patients (mean age, 68.4 years) hospitalized in four-bedded rooms between January 2014 and December 2016....
Article
Background:Decreased light reception because of cataracts leads to potential circadian misalignment, resulting in exacerbation of atherosclerosis; however, little is known about the association between cataracts and atherosclerosis in populations. Methods and Results:In this cross-sectional study, cataracts were graded using slit lamp biomicroscopy...
Article
Purpose: To evaluate the effect of vessel calcification on in-stent restenosis (ISR) after drug-coated stent (DCS) placement in the femoropopliteal segment. Materials and Methods: A retrospective multicenter study was undertaken involving 220 consecutive symptomatic patients (mean age 73.1±8.3 years; 175 men) with femoropopliteal lesions in 230 lim...
Article
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....
Article
Objectives: Controlled artificial daylight exposure, such as light therapy, is effective in bipolar depression, but the association between uncontrolled daytime light and depressive symptoms in bipolar disorder (BD) is unclear. This study investigated the association between daytime light exposure under real-life situations and depressive symptom...
Article
Purpose: To determine whether the presence of glaucoma is associated significantly with nighttime blood pressure (BP) and dipping pattern. Design: Observational, cross-sectional study. Participants: We assessed 109 glaucoma patients (mean age, 71.0 years) from the Longitudinal Study of Biological Circadian Rhythms in Glaucoma Patients: Home Te...
Article
Objectives: To evaluate the associations between pre-awake light (PAL) exposure and subjective and objective measures of sleep quality. Methods: In this cross-sectional study of 1108 elderly participants (mean age, 71.9 years), we measured bedroom light intensity using a bedside light meter for two nights and sleep quality using actigraphy and a...
Article
The present study aimed to determine the relationship between cataract subtypes and circadian blood pressure (BP) variability in elderly individuals. In this cross-sectional study of a community-based cohort, we assessed bilateral lens opacity using slit lamp photographs of 458 elderly individuals (mean age, 69.1 years). Cataract status was defined...
Article
Background Glaucoma may cause physiological and behavioural circadian misalignment because of the loss of intrinsically photosensitive retinal ganglion cells, the primary receptors of environmental light. Although studies have suggested a high prevalence of depression in patients with glaucoma, it is unclear whether the association is independent o...
Article
Objective: Reportedly, melatonin protects the pancreatic islets and decreases insulin resistance; thus, it may contribute to preventing diabetes. Epidemiological data suggested that lower melatonin secretion is associated with higher incidence of diabetes in female nurses. Such associations are unknown in the general population. We evaluated the a...
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Background: Bright light therapy and exercise interventions are effective methods for treating seasonal and non-seasonal affective disorders. Synchronization of internal circadian rhythms with the external environment by light therapy and physical activity may partly explain its efficacy. In the present study, we objectively measured daytime light...
Article
The association between chronic kidney disease (CKD), serum levels of asymmetric dimethylarginine (ADMA), and sleep quality has not been studied in large populations. In this cross-sectional study of 1115 elderly individuals (mean age, 71.9 years), we measured serum levels of ADMA, and objective and subjective sleep quality using actigraphy and a s...
Article
Light is crucial for the synchronization of internal biological rhythms with environmental rhythms. Hospitalization causes a range of unfavorable medical conditions, including delirium, sleep disturbances, depressed mood, and increased fall, especially in elderly people. The hospital room environment contributes significantly to patients’ circadian...
Article
The purpose of this short review is to describe the influence of housing environment temperature and lighting on circadian blood pressure (BP) variability using data from the HEIJO-KYO cohort, a community-based cohort study launched in 2010. Increased excess mortality from cardiovascular disease in winter is a worldwide problem. Previous studies sh...
Article
Background:Detection of aortic aneurysm (AA) prior to rupture is crucial to decreasing its mortality. Towards this purpose, a novel detection algorithm was developed from pulse volume recording (PVR), analyzing the propagation loss of pulse waves caused by expansion of the aortic wall. The diagnostic ability of the algorithm was evaluated in this p...
Article
Objectives: Night-time blood pressure (BP) - prognostically more important than circadian BP variability - has not been evaluated for quantitative associations with objective sleep quality in large populations. Methods: The cross-sectional study measured actigraphic sleep parameters and night-time BP for two nights in 1101 elderly participants....
Article
Our research includes some strengths and limitations. The most important strength is objective measurement of light at night (LAN) intensity using a bedside light meter. Most previous studies evaluating the association between LAN and health outcomes have assessed indoor LAN levels using a self-reported questionnaire or outdoor LAN levels using sat...
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Full-text available
Background: Excess mortality from cardiovascular disease during cold seasons is a worldwide issue. Although some physiologic studies suggests that platelet activation via cold exposure may cause an increased incidence of cardiovascular disease in winter, the influence of indoor cold exposure in real-life situations on platelet (PLT) count remains...
Article
Objectives: Previous epidemiological studies have suggested a cross-sectional association between nocturia and depressive symptoms. The purpose of this study was to evaluate the association between nocturia and the incidence of depressive symptoms. Participants and methods: Of 1127 participants in the HEIJO-KYO population-based cohort, 866 elder...
Article
Objective Breakfast skipping is reported to be associated with obesity in children and younger populations; however, few studies report the association among elderly. The purpose of this study was to investigate the relationships between breakfast skipping and obesity prevalence among elderly. Design: Crosssectional study. SettingCommunity-dwelling...
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Full-text available
Benzidine (BZ) and beta-naphthylamine (BNA) have been classified as definite human carcinogens for bladder cancer by the International Agency for Research on Cancer. However, the epidemiological evidence for an association between exposure to BZ and/or BNA and lung cancer has been inconclusive. We conducted a systematic review and meta-analysis to...
Article
Chronic low-grade systemic inflammation increases cardiovascular risk and mortality. Subjective assessment of sleep quality in previous observational studies has demonstrated associations with biomarkers of systemic inflammation, although the results are conflicting. In this cross-sectional study on 1098 elderly individuals, circulating white blood...
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Objective: To investigate independent effects of various factors associated with sleep disturbance among community-dwelling elderly individuals. Methods: We analyzed data obtained from 3732 individuals aged ≥65 years who responded to a self-administered questionnaire and participated in a structured interview which assessed the Pittsburgh Sleep...
Article
Background: Decreased muscle strength is associated with functional limitation and disability and is a predictor of cardiovascular and all-cause mortality. Recently, oxidative stress and inflammation have been shown to contribute to the loss of muscle strength, and although melatonin has antioxidative and anti-inflammatory properties, the associati...
Article
Background and objectives: Although previous studies suggested that nighttime BP is elevated in diabetes mellitus, the association between prediabetes and nighttime BP remains unclear. In addition, the relationship between diabetic status, renal function, and nighttime BP has not been evaluated in large populations. Design, setting, participants,...
Article
Objective: This study aimed to assess the reliability and validity of Japanese versions of the KIDSCREEN-27 (J-KIDSCREEN-27) and KIDSCREEN-10 (J-KIDSCREEN-10) questionnaires, which are shorter versions of the KIDSCREEN-52 (J-KIDSCREEN-52). Methods: The present analyses are based on a pre-existing dataset of the J-KIDSCREEN-52 validation study, i...
Article
Muscle strength and gait speed are related with functional limitations and disabilities and also predict cardiovascular and all-cause mortality. Nitric oxide (NO) plays an important role in regulating physiological process in skeletal muscles; however, the association between serum asymmetric dimethylarginine (ADMA) level, an endogenous competitive...
Article
Cataract surgery improves visual acuity and drastically increases the capacity for light reception to the retina. Although previous studies suggested that both light exposure and visual acuity were associated with cognitive function, the relationships between cataract surgery, visual acuity, and cognitive function have not been evaluated in large p...
Article
Objectives: To investigate the association between indoor cold exposure and the prevalence of nocturia among elderly, we conducted the present study. Subjects and methods: Temperature in the living room and bedroom of 1065 home dwelling elderly volunteers (≥60 years) was measured for 48 h. Nocturia (≥2 voids per night) and nocturnal urine produc...
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Background: Increased mortality from cardiovascular disease in winter is partly explained by increased blood pressure (BP) caused by cold exposure. For physicians, instruction in home heating is feasible option to reduce cold exposure, but the effectiveness remains unknown. Objectives: To determine whether instruction in home heating increases i...
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Full-text available
In contrast with randomized controlled trials, observational studies have suggested that physiological levels of melatonin are reduced in patients with dementia or depression but the relationship has not been evaluated in large populations. To determine the relationships between physiological levels of melatonin and cognitive function and depressiv...
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Full-text available
Cataract surgery (CS) drastically increases the capacity for light reception to the retina. Several previous studies have suggested the beneficial effect of CS on subjectively measured sleep quality; however, the association between CS and objectively measured sleep quality remains uncertain. To evaluate the association between CS and objectively m...
Article
Difficulty in initiating sleep is an important problem because it is associated with an increased incidence of depression, diabetes, myocardial infarction, and higher all-cause mortality. Although experimental studies in controlled settings have shown that warm skin temperature of the extremities (feet and hands) before bedtime is associated with s...
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Blue light information plays an important role in synchronising internal biological rhythm within the external environment. Circadian misalignment is associated with the increased risk of sleep disturbance, obesity, diabetes mellitus, depression, ischaemic heart disease, stroke and cancer. Meanwhile, blue light causes photochemical damage to the re...
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To evaluate the association between nocturnal void frequency and ambulatory blood pressure (BP). Cross-sectional. Nara, Japan. Community-based elderly individuals (mean age 72.1, N = 867). Nocturnal void frequency and ambulatory BP. Two hundred twenty-four participants had no nocturnal void, 384 had one nocturnal void, and 259 had two or more noctu...
Article
A significant association between nocturia and subjective sleep quality has previously been reported; however, the association between nocturia and objective sleep quality remains unclear. The purpose of this study was to evaluate the quantitative association between nocturnal voiding (NV) frequency and objective sleep quality in a large, general,...
Article
Circulating white blood cell (WBC) and platelet (PLT) counts are widely available and inexpensive cellular biomarkers of systemic inflammation and have been associated with a risk of cardiovascular disease, cancer, and mortality. Melatonin may reduce systemic inflammation through its direct and indirect anti-oxidative effect; however, the associati...
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Full-text available
Light information is the most important cue of circadian rhythm which synchronizes biological rhythm with external environment. Circadian misalignment of biological rhythm and external environment is associated with increased risk of depression, insomnia, obesity, diabetes, cardiovascular disease, and cancer.Increased light transmission by cataract...
Article
The present study aimed to assess the reliability and validity of the Japanese version of KIDSCREEN-52 (J-KIDSCREEN-52), a generic questionnaire used to assess health-related quality of life (HRQOL) among children/adolescents and parents/proxies. We conducted a school-based study, in which 1564 children and adolescents aged 8-18 years and their 132...
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Full-text available
Background: Melatonin decreases night-time blood pressure (BP) by increasing nitric oxide (NO) in endothelial cells. Whether serum asymmetric dimethylarginine (ADMA), a major endogenous competitive inhibitor of endothelial NO synthase, attenuates the association of melatonin with night-time BP and dipping in humans is unclear. METHODS AND RESULTS:...
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Full-text available
Epidemiological and cellular biological studies indicate the influence of impaired circadian biological rhythmicity on atherosclerosis. Increased exposure to light at night (LAN) is common in modern life, and LAN exposure is the most important environmental cue for circadian misalignment. However, the association between LAN exposure and atheroscle...
Article
Full-text available
Risk for lung cancer in workers exposed to benzidine (BZ) and/or beta-naphthylamine (BNA), which are well-known bladder carcinogens, has been examined in many epidemiological studies, but individual epidemiological studies generally lack the power to examine the association between BZ/BNA exposure and lung cancer. We conduct a systematic review and...
Article
Full-text available
Background: Melatonin is associated with a variety of diseases in advanced age, including insomnia, depression, and dementia, and its secretion is influenced by light exposure. Although studies in young and middle-aged subjects have shown that females tend to have higher melatonin levels than males, gender differences in melatonin levels among old...
Article
Purpose: To evaluate non-urological cancer risks associated with benzidine (BZ) and beta-naphthylamine (BNA), a historical cohort study was undertaken. Methods: A total of 224 male workers exposed to BZ/BNA from a single factory were followed from 1953 to 2011. To estimate BZ/BNA exposure dose, duration of exposure (DOE) was defined as duration...