title: Diurnal variation of urinary sodium-to-potassium ratio in free-living Japanese individuals.
abstract: High sodium-to-potassium ratios are associated with elevated blood pressure levels and an increased risk of cardiovascular diseases. We aimed to determine whether urinary sodium-to-potassium ratios fluctuate diurnally during the day to understand measured values of casual urinary sodium-to-potassium ratios. A total of 13,277 casual urine specimens were collected under free-living conditions from 122 Japanese normotensive and hypertensive individuals. Participants collected all casual urine samples in aliquot tubes, reported urine volumes and the time at each voiding for 10-22 days. Then, specimens were classified into hourly data. Diurnal patterns of urinary sodium-to-potassium ratios and urinary concentrations of sodium and potassium were evaluated. Overall mean values of hourly urinary sodium-to-potassium ratios were highest (4.1-5.0) in the early morning, lower (3.3-3.8) in the daytime and higher (4.0-4.4) toward evening hours. The mean urinary sodium and potassium concentrations were the lowest (90-110 and 24-32 mmol l-1, respectively) during the early morning and higher (110-140 and 35-43 mmol l-1, respectively) after mid-morning. Diurnal variability of potassium concentrations was larger than for sodium concentrations. Diurnal variations in urinary sodium-to-potassium ratios were comparable between normotensive and hypertensive individuals, between hypertensive individuals with and without antihypertensive medications, and among age and gender-specific subgroups. Overall mean hourly urinary sodium-to-potassium ratios fluctuated diurnally under free-living conditions and were higher during the morning and evening and lower during the daytime compared with 24-h urinary sodium-to-potassium ratios. Diurnal variation in urinary sodium-to-potassium ratios should be considered to understand actual daily dietary levels and avoid over- and under-estimation in clinical practice.
authors.affiliation: Department of Research and Development, OMRON Healthcare Co., Ltd., Muko, Japan.|Department of Public Health, Shiga University of Medical Science, Otsu, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Iwahori
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Otsu, Japan.|Center for Epidemiologic Research in Asia, Shiga University of Medical Science, Otsu, Japan.
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Ueshima
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Otsu, Japan.
authors.forename: Sayuki
authors.initials: S
authors.lastname: Torii
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Otsu, Japan.|Department of Nursing, Aino University, Ibaraki, Japan.
authors.forename: Yoshino
authors.initials: Y
authors.lastname: Saito
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Otsu, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Kondo
authors.affiliation: Department of Medical Statistics, Shiga University of Medical Science, Otsu, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tanaka-Mizuno
authors.affiliation: Department of Preventive Medicine and Public Health, Fukuoka University, Fukuoka, Japan.
authors.forename: Hisatomi
authors.initials: H
authors.lastname: Arima
authors.affiliation: Department of Public Health, Shiga University of Medical Science, Otsu, Japan.|Center for Epidemiologic Research in Asia, Shiga University of Medical Science, Otsu, Japan.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Miura
mesh_terms: D000328:Adult; D000368:Aged; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000652:urine*; D012964:Sodium / Q000652:urine*
chemical_list: D012964:Sodium; D011188:Potassium