title: Association between light exposure at night and nighttime blood pressure in the elderly independent of nocturnal urinary melatonin excretion.
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.
authors.affiliation: Department of Community Health and Epidemiology, Nara Medical University School of Medicine , Nara , Japan .
authors.forename: Kenji
authors.initials: K
authors.lastname: Obayashi
authors.forename: Keigo
authors.initials: K
authors.lastname: Saeki
authors.forename: Junko
authors.initials: J
authors.lastname: Iwamoto
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Ikada
authors.forename: Norio
authors.initials: N
authors.lastname: Kurumatani
mesh_terms: D056044:Actigraphy; D000367:Age Factors; D000368:Aged; D001794:Blood Pressure / Q000528:radiation effects*; D018660:Blood Pressure Monitoring, Ambulatory; D002940:Circadian Rhythm / Q000528:radiation effects*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006973:Hypertension / Q000175:diagnosis / Q000401:mortality / Q000503:physiopathology*; D007564:Japan; D008027:Light / Q000009:adverse effects*; D008029:Lighting; D008297:Male; D008550:Melatonin / Q000652:urine*; D012307:Risk Factors; D013997:Time Factors
chemical_list: D008550:Melatonin
keywords: Actigraphy; circadian rhythm; elderly; light at night; melatonin; nighttime blood pressure