title: Daytime cold exposure and salt intake based on nocturnal urinary sodium excretion: A cross-sectional analysis of the HEIJO-KYO study.
abstract: Increased cardiovascular incidence in winter is partly explained by higher blood pressure due to cold exposure. Although higher salt intake induced by cold exposure has been reported in mice, the association remains unclear in humans. To investigate the association between salt intake and cold exposure in winter, a cross-sectional study was conducted among 860 elderly subjects (mean ± standard deviation: 72.0 ± 7.1 years). We determined ambient temperature at every 10 min according to indoor temperature measured in the subjects' home, outdoor temperature, and self-administered diary logging time spent outdoors. Salt intake was estimated by nocturnal sodium excretion rate of overnight urine collection. A 1°C lower daytime ambient temperature was significantly associated with a higher urinary sodium excretion rate by 0.07 mmol/h in the subsequent night independent of age, sex, body weight, alcohol intake, calcium channel blocker use, diabetes, household income, estimated glomerular filtration rate, daytime physical activity (p=0.02). After further adjustment for outdoor temperature and day length, the lowest tertile groups of ambient daytime temperature (10.1 ± 2.3°C) showed the nocturnal urinary sodium excretion rate was higher by 14.2% (7.62 vs. 6.54 mmol/h) compared with the highest tertile group (19.3 ± 1.8°C). Higher sodium excretion rate was associated with higher nighttime ambulatory blood pressure (p<0.01) and its lower nocturnal dipping (p<0.01). Significant association between higher salt intake and daytime cold exposure partly explain the mechanism of higher blood pressure in winter, and suggest that a reduction of cold exposure might be effective to decrease salt intake.
authors.affiliation: Department of Community Health and Epidemiology, Nara Medical University School of Medicine, Nara, Japan. Electronic address: saekik@naramed-u.ac.jp.
authors.forename: Keigo
authors.initials: K
authors.lastname: Saeki
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.affiliation: Center for Academic Industrial and Governmental Relations, Nara Medical University School of Medicine, Nara, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Tone
authors.affiliation: Department of Community Health and Epidemiology, Nara Medical University School of Medicine, Nara, Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Kurumatani
mesh_terms: D056044:Actigraphy; D000368:Aged; D001794:Blood Pressure / Q000502:physiology; D003080:Cold Temperature / Q000009:adverse effects; D003430:Cross-Sectional Studies; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D006798:Housing; D006801:Humans; D007564:Japan / Q000453:epidemiology; D016014:Linear Models; D008297:Male; D009043:Motor Activity / Q000502:physiology; D015999:Multivariate Analysis; D017440:Photoperiod; D011446:Prospective Studies; D012959:Socioeconomic Factors; D012982:Sodium, Dietary / Q000008:administration & dosage / Q000652:urine
chemical_list: D012982:Sodium, Dietary
keywords: Ambulatory blood pressure monitoring; Cold exposure; Indoor temperature; Nocturnal urinary sodium excretion rate; Outdoor temperature