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.

Urinary Sodium-to-Potassium Ratio Tracks the Changes in Salt Intake during an Experimental Feeding Study Using Standardized Low-Salt and High-Salt Meals among Healthy Japanese Volunteers

“…Thus, the single-day 24-h urine collection on the last day of LS and HS diet periods reasonably represented the group estimate of Na intake during these periods, as the day-to-day variation in Na excretion was minimized by means of the standardized diets. Additionally, the urinary Na/K ratio is known to show diurnal variation [ 38 ]. Thus, daily repetitive spot urine Na/K ratio sampling may have corrected the effect of diurnal variation and therefore show a good association with dietary salt intake and the 24-h urine Na/K ratio under controlled dietary conditions.…”

Sodium and Potassium Intakes and Their Ratio in Adults (18–90 y): Findings from the Irish National Adult Nutrition Survey

“…The 24-h Na excretions were compared to the EFSA AI of 2.0 g/d [3] and the 24-h K excretions were compared to the EFSA AI of Nutrients 2020, 12, 938 4 of 12 3500 mg/d [7]. Urinary molar Na:K was calculated for each participant as Na (mmol/L)/K(mmol/L), with a value of 0.6 being subtracted from each individual value to correct for timing bias associated with circadian rhythms [42]. Compliance with Na:K target molar ratios was examined by assessing the proportion of the population complying with the WHO guideline of ≤1.0 and the suggested suboptimal target of ≤2.0 [11,19].…”

Time to Consider Use of the Sodium-to-Potassium Ratio for Practical Sodium Reduction and Potassium Increase

“…There are several benefits for using the casual urine estimate for the 24- h urine value used to determine the Na/K ratio. These benefits include the independence of the urine volume, creatinine excretion, and body weight, the fact that repeated random sampling minimizes the systemic error caused by diurnal variation and day-to-day variation in the Na/K ratio [ 69 ], that there is less bias observed in the low to high salt range, and that the gold standard set for the casual urine estimate is the 7-day 24- h urine when the single day 24- h urine value is used for Na and K separately [ 67 , 68 ]. Therefore, the repeated casual urine Na/K ratio measurement may be one of the most reliable individual estimates for assessing intakes involved with Na reductions and K increases in normotensive and hypertensive individuals.…”