Urinary cations and blood pressure: a collaborative study of 16 districts in China.

Relationships between blood pressure and overnight urinary sodium, potassium and calcium were investigated in 3248 subjects from 16 districts in China. Average systolic (SBP) and diastolic (DBP) blood pressures of subjects from northern, middle and southern China were 116/74.2, 114/70.5 and 110.8/69.6 mmHg, respectively. Urinary sodium, potassium and calcium were 55.1, 8.3 and 1.1 mmol/l for the north, 63.6, 9.2 and 1.6 mmol/l for the middle and 50.0, 8.9 and 1.5 mmol/l for the south, respectively. The urinary sodium to potassium ratio was significantly and positively correlated with SBP and DBP in both males and females. Urinary sodium was weakly and positively correlated with SBP only in the north. Females over the age of 50 years were especially sensitive to sodium intake. Urinary calcium was negatively correlated with DBP in both males and females. Urinary calcium (creatinine) was negatively correlated with SBP in males, and with SBP and DBP in the south. Urinary potassium was negatively correlated with SBP and DBP only in the 20-29 year age group. Urinary potassium (creatinine) was negatively correlated with DBP only in the south. Age and body mass index were positively and level of education negatively correlated with blood pressure. Dietary factors for higher blood pressure in northern China were related to higher sodium, lower potassium and possibly lower calcium intake.