Effect of alteration in sodium chloride intake on blood pressure of normotensive subjects.

Sodium intake was altered for 2-week periods in 201 volunteers with no history of hypertension. Systolic and diastolic blood pressure was higher with a high sodium intake (200 mmol) compared with the values for a reduced intake (70 mmol). The rise in supine systolic and diastolic blood pressure in subjects over 50 years was 15/8 mm Hg, which was larger than the increase of 2.5/2.3 mm Hg measured in younger people. In the younger age group blood pressure changed with diet in approximately 15%. Individuals with a family history of hypertension were more likely to have a rise in blood pressure when sodium intake was increased. Patients were subdivided into responders and nonresponders according to the change in blood pressure with a different sodium intake. Creatinine clearance with a reduced sodium intake was lower in the responders compared with the values for the nonresponders. In the responders creatinine clearance increased as sodium intake increased and with the high sodium intake was not different in the two groups. In subjects who had a rise in blood pressure with increasing sodium load, plasma volume fell, while it rose in the nonresponders. These studies demonstrate that increased sodium intake causes blood pressure to rise in normotensive individuals. Renal function is less in those who have a rise in blood pressure when extra sodium is consumed. Changes in plasma volume indicate that the link between sodium intake and hypertension does not involve plasma volume.