24-Hour Urinary Collection Data Support Strong Associations between Sodium and Potassium Excretion and Blood Pressure in the National Health and Nutrition Examination Survey

By Kristen N Smith, PhD, RD, LD; Mary R Dicklin, PhD; Kevin C Maki, PhD


It is well established that hypertension is an important modifiable risk factor for cardiovascular disease (CVD), which is a leading cause of morbidity and mortality in the United States.2 Excess dietary sodium has been associated with increased blood pressure.3-5 Conversely, higher intake of potassium has been associated with lower blood pressure.6 The ratio of sodium-to-potassium may have a stronger association with blood pressure than either of the two components alone.7

The majority of studies that have examined the above associations have used self-reported dietary measures to estimate intakes. This includes the National Health and Nutrition Examination Survey (NHANES), which has mainly utilized 24-hour dietary recalls. These tactics are fraught with limitations and may not provide a complete and accurate picture due to inaccuracies in self-led data collection and participant recall. Twenty-four-hour dietary recalls may underestimate average sodium intake by 4 to 34% in comparison with 24-hour urinary excretion.8,9

In an examination of 2014 NHANES data, researchers hypothesized that higher sodium excretion (reflecting higher intake) and a greater sodium-to-potassium ratio would be significantly associated with higher blood pressure and odds of hypertension, whereas greater potassium excretion (reflecting higher intake) would be inversely associated with blood pressure and odds of hypertension.


Cross-sectional data were gathered and analyzed from the 2014 NHANES, a nationally representative survey of noninstitutionalized persons in the United States. One half of NHANES non-pregnant participants (age 20 to 69 years) who were examined in the Mobile Examination Center were included in the 24-hour urine collection study (n=1103). Data gathered from 766 participants with complete blood pressure and 24-hour urine collections were included in the analysis with results described below.


Among the participants included in the analysis, over half were classified as hypertensive (weighted prevalence, 28.2%; 95% confidence interval [CI], 21.6-34.8) or prehypertensive (23.1%; 95% CI, 19.5-26.6). Excretion of sodium, potassium and the sodium-to-potassium ratio did not differ by hypertension status (after adjustment for age, sex, race/ethnicity and body mass index).

Sodium excretion (per 1000 mg/d higher) was directly associated with systolic blood pressure (SBP) (4.58 mm Hg; 95% CI, 2.64-6.51) and diastolic blood pressure (DBP) (2.25 mm Hg; 95% CI, 0.83-3.67). Potassium excretion (per 1000 mg/d higher) was inversely associated with SBP (-3.72 mm Hg; 95% CI -6.01 to -1.42). Molar sodium-to-potassium ratio (per 0.5 U higher) was directly associated with SBP (1.72 mm Hg; 95% CI, 0.76-2.68). In the fully adjusted multivariable logistic model, persons within the highest quartile in comparison with the lowest quartile of sodium excretion had significantly greater odds of having hypertension (odds ratio, 4.22; 95% CI, 1.36-13.15).






Beta-coefficient (95% CI)1

Sodium excretion

4.58* (2.64 to 6.51)

2.25* (0.83 to 3.67)

Potassium excretion

-3.72* (-6.01 to -1.42)

-0.25 (-1.91 to 1.42)

Sodium-to-potassium ratio

1.72* (0.76 to 2.68)

0.30 (-0.53 to 1.12)

1Beta-coefficents for sodium and potassium excretion indicate change in mm Hg of blood pressure associated with 1000 mg/d change in excretion. Beta-coefficients for the ratio represent change in mm Hg blood pressure associated with 0.5 U change in molar ratio. Fully adjusted for age, sex, race/ethnicity plus body mass index, education, history of CVD, diabetes status, chronic kidney disease, smoking status and physical activity. Models examining sodium excretion were simultaneously adjusted for potassium excretion, and vide versa.

*p < 0.01 for beta-coefficient in the regression model.


NHANES’ first ever use of the “gold standard” 24-hour urine collection identified a direct association between sodium excretion and blood pressure among US adults.1 Analyses of these cross-sectional data also demonstrated that the sodium-to-potassium ratio was directly associated with SBP, whereas potassium excretion was inversely associated with SBP. These results align with previous findings from studies examining urinary electrolyte excretion and blood pressure.10-12 These conclusions provide additional support for the 2015-2020 Dietary Guidelines for Americans containing the advice to reduce sodium intake and increase intake of potassium-containing foods compared with the current average American diet.13


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