Development and preliminary validation of a prediction formula of sodium and sodium-to-potassium ratio based on multiple regression using 24-h urines

Accurate measurement of sodium intake in the diet is challenging, and epidemiological studies can be hampered by the attenuation of associations due to measurement error in sodium intake. A prediction formula for habitual 24-h urine sodium excretion and sodium-to-potassium ratio might lead to more reliable conclusions. Five 24-h urinary samples and two Food Frequency Questionnaires (FFQs) were conducted among 244 Japanese participants aged 35-80 years. We conducted multivariate linear regression analysis with urinary excretion as dependent variables and eating behaviour and food frequency as independent variables. Empirical weights of sodium excretion and sodium-to-potassium ratio were extracted. Preliminary validity was also assessed by randomly dividing the subjects into development and validation groups based on the correlation coefficient between estimates by the prediction formula and urinary excretion. Taste preference, soy sauce use at the table, frequency of pickled vegetables intake and number of bowls of miso soup were extracted as determinants of sodium excretion. Correlation coefficients between the estimates and urinary excretion for men and women were 0.42 and 0.43, respectively, for sodium and 0.49 and 0.50, respectively, for sodium-to-potassium ratio. This prediction formula may provide more accurate estimation of sodium intake and sodium-to-potassium ratio than the food composition approach.

Association between the extent of house collapse and urine sodium-to-potassium ratio of victims affected by the 2011 Great East Japan Earthquake and Tsunami: a cross-sectional study

People who experience natural disasters have a high risk of developing cardiovascular diseases. We investigated the association between the extent of house collapse and urine sodium-to-potassium (UNa/K) ratio of 2011 Great East Japan Earthquake victims. We used the baseline survey data of the Tohoku Medical Megabank Project Community-Based Cohort Study of 29 542 individuals (aged 20-74 years) residing in the affected areas. The UNa/K ratio was calculated using spot urinary electrolyte values. Analysis of covariance was used to calculate the multivariate-adjusted geometric means of the UNa/K ratio in the following groups stratified according to the self-reported extent of house collapse: total collapse (TC), half collapse (HC), partial collapse (PC), and no damage (ND). Multivariable-adjusted odds ratios (ORs) for a high UNa/K ratio were calculated using logistic regression. The TC, HC, PC, and ND groups comprised 5 359 (18.1%), 3 576 (12.1%), 7 331 (24.8%), and 13 276 (44.9%) participants, respectively. The TC (3.33; 95% confidence interval [CI], 3.28-3.38), HC (3.37; 3.30-3.43), and PC (3.32; 3.28-3.37) groups had significantly higher multivariate-adjusted geometric means of the UNa/K ratio than the ND (3.24; 3.21-3.27) group. The multivariable-adjusted ORs (95% CIs) for a high UNa/K ratio in the TC, HC, and PC groups vs. the ND group were 1.07 (0.99-1.15), 1.20 (1.11-1.31), and 1.20 (1.12-1.28), respectively. Similar associations between house collapse and UNa/K ratio were observed for both sexes. We report that victims of a natural disaster tend to have a diet with high sodium-to-potassium ratio.

Urinary sodium-to-potassium ratio and intake of sodium and potassium among men and women from multiethnic general populations: the INTERSALT Study

The Na/K ratio may be more strongly related to blood pressure and cardiovascular disease than sodium or potassium. The casual urine Na/K ratio can provide prompt on-site feedback, and with repeated measurements, may provide useful individual estimates of the 24-h ratio. The World Health Organization has published guidelines for sodium and potassium intake, but no generally accepted guideline prevails for the Na/K ratio. We used standardized data on 24 h and casual urinary electrolyte excretion obtained from the INTERSALT Study for 10,065 individuals aged 20-59 years from 32 countries (52 populations). Associations between the casual urinary Na/K ratio and the 24-h sodium and potassium excretion of individuals were assessed by correlation and stratification analyses. The mean 24-h sodium and potassium excretions were 156.0 mmol/24 h and 55.2 mmol/24 h, respectively; the mean 24-h urinary Na/K molar ratio was 3.24. Pearson's correlation coefficients (r) for the casual urinary Na/K ratio with 24-h sodium and potassium excretions were 0.42 and -0.34, respectively, and these were 0.57 and -0.48 for the 24-h ratio. The urinary Na/K ratio predicted a 24-h urine Na excretion of <85 mmol/day (the WHO recommended guidelines) with a sensitivity of 99.7% and 94.0%, specificity of 39.5% and 48.0%, and positive predictive value of 96.3% and 61.1% at the cutoff point of 1 in 24 h and casual urine Na/K ratios, respectively. A urinary Na/K molar ratio <1 may be a useful indicator for adherence to the WHO recommended levels of sodium and, to a lesser extent, the potassium intake across different populations; however, cutoff points for Na/K ratio may be tuned for localization.