Urinary sodium-to-potassium ratio: a simple and useful indicator of diet quality in population-based studies

Background: Current evidence regarding the prognostic relevance of urinary sodium-to-potassium ratio (Na-to-K ratio), as an indicator of diet quality is limited. This study was conducted to investigate whether urinary Na-to-K ratio could be related to habitual dietary patterns, in a general population. Methods: This study was conducted in the framework of the Tehran Lipid and Glucose Study (2014-2017) on 1864 adult men and women. Urinary Na and K concentrations were measured in the morning spot urine samples. Dietary intakes of the participants were assessed using a validated 147-item Food Frequency Questionnaire (FFQ) and major dietary patterns were obtained using principal component analysis. Mediterranean dietary pattern and Dietary Approaches to Stop Hypertension (DASH) score, were also calculated. Multivariable-adjusted linear regression was used to indicate association of dietary patterns and urinary Na-to-K ratio. Results: Mean (+/- SD) age of participants was 43.7 +/- 13.9 years and 47% were men. Mean (+/- SD) urinary Na, K and the ratio was 139 +/- 41.0 and 57.9 +/- 18.6 mmol/L, 2.40 +/- 0.07, respectively. Higher urinary Na-to-K ratio (> 2.37 vs. < 1.49) was related to lower intakes of vegetables (282 vs. 321 g/day), low-fat dairy (228 vs. 260 g/day) and fruits (440 vs. 370 g/day). Western dietary pattern was related to higher urinary Na-to-K ratio (beta = 0.06; 95% CI 0.01, 0.16). Traditional dietary pattern, Mediterranean and DASH diet scores were inversely associated with urinary Na-to-K ratio (beta = - 0.14; 95% CI - 0.24, - 0.11, beta = - 0.07; 95% CI - 0.09, - 0.01, beta = - 0.12; 95% CI - 0.05, - 0.02, respectively). Conclusions: Spot urinary Na-to-K ratio may be used as a simple and inexpensive method to monitor diet quality in population-based epidemiological studies.