Relationship of Blood Pressure to Sodium and Potassium Excretion in Japanese Women

The cross-sectional association of blood pressure with urinary sodium and potassium excretion was investigated with a stepwise regression analysis. Spot urine of 7441 females between 40 and 69 years was collected from 169 municipalities (88 urban and 81 rural) covering all prefectures in Japan. The filter paper sampling technique for urine was used to collect samples of subjects from March to December in 1985. Spot urine samples were analyzed for sodium, potassium and creatinine. In addition, 24-hr sodium and potassium excretions were estimated by predictive equations. Blood pressure, sodium excretion and sodium potassium ratios were higher in rural areas than in urban areas. Consistent positive correlations between urinary sodium and blood pressure, and negative correlations between urinary potassium and blood pressure were observed in the whole country of Japan, in both urban and rural areas, and also in separate observations of twelve regions in Japan with some exceptions. When compared in standardized partial regression coefficients, relative effects of potassium on systolic blood pressure were higher than those of sodium in the whole of Japan, in urban and rural areas, and in five among the twelve regions. The present Japanese study confirmed a positive within-population relationship between sodium excretion and blood pressure and a negative relationship between potassium excretion and blood pressure.