Relationship between ambulatory and resting blood pressure responses to dietary salt restriction in normotensive men

OBJECTIVE: To examine the relationship between changes in resting and ambulatory blood pressures induced by dietary salt restriction in 90 young normotensive men. METHODS: Subjects were given a standardized low-salt diet containing 20 mmol sodium chloride per day for 14 days. To this diet, a daily supplement of 20 tablets of slow sodium (10 mmol NaCl per tablet) or placebo was added in a randomized single-blind cross-over fashion for 7 days. The ambulatory blood pressure was measured on the sixth day and the resting blood pressure was measured on the seventh day of each dietary period. RESULTS: Although salt intake did not affect blood pressure levels in the whole group, the response of the blood pressure was quite variable among individual subjects. Salt-induced changes in resting systolic (r = 0.30, P = 0.006) and mean (r = 0.27, P = 0.014) blood pressures, but not diastolic blood pressure, were correlated positively to changes in daytime ambulatory blood pressure. The changes in resting systolic and mean blood pressures were also correlated significantly to the nocturnal falls in systolic (r = 0.26, P = 0.015) and mean (r = 0.27, P = 0.012) blood pressure levels and heart rate (r = 0.26, P= 0.015) under the high-salt diet. Diet-induced changes in resting mean blood pressure were correlated significantly to the daytime ambulatory blood pressure (r = 0.30, P < 0.005) and the resting heart rate (r = 0.24, P < 0.02) under the high-salt diet. CONCLUSION: Salt-induced changes in resting blood pressure in young normotensive men are correlated positively to changes in ambulatory daytime blood pressure levels as well as to the daytime ambulatory blood pressure and the nocturnal fall in blood pressure under a high-salt diet. These findings suggest that dietary salt-intake restriction can lower both resting and daytime ambulatory blood pressure levels in some normotensive individuals who may be predisposed to the development of hypertension.