Water sodium, urinary electrolytes, and blood pressure of adolescents.

Blood pressure measurements were made on children in their fourth year at secondary schools in parts of Scunthorpe Health District supplied with drinking water of varying sodium content. Of the 3131 children, 2740 were examined (1394 boys and 1346 girls). Boys had slightly higher systolic pressures and slightly lower diastolic pressures than the girls. There was no difference between the blood pressure distributions of children in areas supplied with water containing 105 mg/l sodium, 50 mg/l sodium, or less than 15 mg/l sodium. Small differences were found in the weights of children in these areas, and slightly more of the children in the area supplied with water containing more than 105 mg/l sodium had relatives who had been treated for hypertension. Standardisation for these factors did not show any relation between water salinity and either systolic or diastolic blood pressure. Studies of the urinary sodium, potassium, and the ratios of these to creatinine on a sample of 769 boys showed no correlation with assessments of usual sodium intake, but urinary sodium correlated well with salt and fluid intake at the meal immediately preceding examination. The relation between median blood pressure and urinary sodium concentration and lack of a clear relation with sodium creatinine ratio supports the hypothesis that it may be the ratio of salt to fluid intake rather than total dietary sodium that is relevant to the regulation of blood pressure.