Relationship between salt excretion and blood pressure in various regions of China.

Overnight urine samples were collected on three consecutive days from 3105 persons in 12 regions of China, and analysed for levels of sodium and potassium. The mean 9-hour overnight urine sodium level ranged from 49.51 to 139.12 mmol, and urine potassium from 6.32 to 18.43 mmol. Univariate regression, simple correlation analysis, and multivariate ridge regression analysis were carried out on the data. A positive correlation between blood pressure and urine sodium or sodium/potassium ratio was found in each of the twelve regions. Urine potassium showed a negative correlation with blood pressure in three regions.