Sodium Restriction Shifts Circadian Rhythm of Blood Pressure From Nondipper to Dipper in Essential Hypertension

BACKGROUND: Sodium restriction has been widely used for treatment of hypertension and renal diseases. Whether sodium restriction can transform the circadian rhythm of blood pressure from nondipper to dipper is examined. METHODS AND RESULTS: Patients (n=42) with essential hypertension were maintained on a high-sodium diet (12 to 15 g of NaCl per day) and a low-sodium diet (1 to 3 g/d) for 1 week each. On the last day of each diet, blood pressures were measured noninvasively every hour for 24 hours with an automatic oscillometric device. Twenty-one patients were classified as non-sodium sensitive whereas 21 were classified as sodium sensitive on the basis of a > or = 10% change in 24-hour mean arterial pressure caused by sodium restriction. Nocturnal blood pressure fall was significant in the non-sodium sensitive subjects but not in sodium-sensitive subjects. There was a significant interaction between sodium restriction and nocturnal fall in blood pressure only in the sodium-sensitive subjects, indicating that the degree of the nocturnal fall was affected by sodium restriction. Furthermore, changes in the nocturnal fall induced by sodium restriction had a positive relationship with sodium sensitivity (r=.38, P<.02) and a negative relationship with the nocturnal fall before sodium restriction (r=-.75, P<.0001). CONCLUSIONS: These findings show the difference in nocturnal fall in blood pressure between the non-sodium sensitive and sodium-sensitive types of essential hypertension. The diminished nocturnal fall, recognized in the sodium-sensitive type, is restored by sodium restriction, indicating that the circadian rhythm of blood pressure shifted from a nondipper to a dipper pattern. On the other hand, the nocturnal fall is not affected by sodium restriction in the non-sodium sensitive type, and the circadian rhythm remains of the dipper variety.