Introduction:
Recently, the balance between sodium and potassium intake, i.e. sodium-to-potassium (Na/K) ratio, has received significant attention for prevention of hypertension. Previous studies reported the positive association between urinary Na/K (uNa/K) ratio and hypertension. However, even the same uNa/K ratio value, there might be high Na/ high K ratio or low Na/ low K ratio.
Hypothesis:
We assessed the hypothesis that blood pressure (BP) is higher in high Na/ high K group than that in low Na/ low K group even at the same uNa/K ratio in general population in cross-sectional study.
Methods:
The subjects were 20 to 74 years old who participated in The Tohoku Medical Megabank Project Community-based Cohort Study. Of these participants, we targeted 54,011 subjects (men: 20,505 women: 33,506 mean age: 59.9 years) who had information of BP, urinary Na and K. We estimated 24-h urinary excretion of Na and K using Tanaka formula. Urinary Na and K were each classified into quartiles (Na; Q1~Q4, K; Q1~Q4), and set all 16 groups of uNa/K ratio by combining Na and K respectively. To assess the relationship between casual uNa/K ratio and BP, we performed an analysis of covariance to calculate the adjusted mean systolic BP (SBP). We included covariate factors as age, sex, BMI and alcohol intake. We also assessed the relationship between uNa/K ratio and SBP using multiple regression analyses adjusted for covariate factors. We stratified the participants into two groups: ‘under treatment for hypertension’ (n=17,091) and ‘without treatment for hypertension (n=36,920)’.
Results:
The mean of uNa/K ratio for each group of Na (Q1)/K(Q1), Na (Q2)/K(Q2), Na (Q3)/K(Q3) and Na (Q4)/K(Q4) was all 4.0. As previous report showed, higher uNa/K ratio group showed higher SBP and lower uNa/K group showed lower BP. When we compared adjusted mean SBP of Na (Q1)/K(Q1) and Na (Q4)/K(Q4) the value were comparable, but the value were significantly higher in Na (Q4)/K(Q4) group (The adjusted mean SBP of Na (Q1)/K(Q1), Na (Q2)/K(Q2), Na (Q3)/K(Q3) and Na (Q4)/K(Q4) was 123.6, 124.9, 124.7 and 125.5 mmHg, respectively). The uNa/K was significantly positively associated with SBP independently of age, sex, BMI, and alcohol intake. The finding was unchanged the results in under treatment group.
Conclusions:
BP was significantly higher in high Na/ high K group than in low Na/ low K group even at the same uNa/K ratio. We suggested that not only increasing K intake but also reducing salt is important for preventing hypertension.