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Association of Urinary Sodium and Potassium Excretion With Blood Pressure
Study Questions:
What are the levels of sodium and potassium intake overall and according to urban versus rural area, country income level, and geographic region, and their associations with blood pressure, overall and in key subgroups?
Methods:
The PURE (Prospective Urban Rural Epidemiology) trial investigators studied 102,216 adults from 18 countries. Estimates of 24-hour sodium and potassium excretion were made from a single fasting morning urine specimen and were used as surrogates for intake. They assessed the relationship between electrolyte excretion and blood pressure, as measured with an automated device. Analysis of covariance was performed, with tests for linear trend, to compare the mean blood pressure among groups defined on the basis of sodium excretion or potassium excretion, with adjustment for covariates known to be associated with blood pressure, including age, sex, educational level, body mass index, alcohol intake, and geographic region.
Results:
Regression analyses showed increments of 2.11 mm Hg in systolic blood pressure and 0.78 mm Hg in diastolic blood pressure for each 1-g increment in estimated sodium excretion. The slope of this association was steeper with higher sodium intake (an increment of 2.58 mm Hg in systolic blood pressure per gram for sodium excretion >5 g per day, 1.74 mm Hg per gram for 3-5 g per day, and 0.74 mm Hg per gram for <3 g per day; p < 0.001 for interaction). The slope of association was steeper for persons with hypertension (2.49 mm Hg per gram) than for those without hypertension (1.30 mm Hg per gram, p < 0.001 for interaction), and was steeper with increased age (2.97 mm Hg per gram at >55 years of age, 2.43 mm Hg per gram at 45-55 years of age, and 1.96 mm Hg per gram at <45 years of age; p < 0.001 for interaction). Potassium excretion was inversely associated with systolic blood pressure, with a steeper slope of association for persons with hypertension than for those without it (p < 0.001) and a steeper slope with increased age (p < 0.001).
Conclusions:
The authors concluded that the association of estimated intake of sodium and potassium with blood pressure was nonlinear and was most pronounced in persons consuming high-sodium diets, persons with hypertension, and older persons.
Perspective:
This study reports a positive, but nonuniform association between estimated sodium excretion and blood pressure. Furthermore, the slope of the association was steeper among persons consuming high-sodium diets, those with hypertension than among those without hypertension, and was steeper with increasing age. For estimated potassium excretion, there was a significant inverse association with systolic blood pressure, with steep slopes of association among persons with hypertension, older persons, and obese persons. These findings suggest that assessments of the relationship between sodium intake and blood pressure should take into account the level of sodium intake in the population, the age of the participants, and whether the participants have hypertension.
Keywords: Electrolytes, Potassium, Body Mass Index, Sodium, Dietary, Research Personnel, Blood Pressure, Regression Analysis, Hypertension, Fasting
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