Influence of salt intake on the daytime-nighttime blood pressure variation in normotensive and hypertensive black subjects.
OBJECTIVE
To evaluate the influence of different salt-intake regimens on the circadian rhythm of blood pressure (daytime-night-time relationship) in normotensive and hypertensive black subjects with different patterns of salt sensitivity.


METHODS
Randomized, cross-over study. Twenty normotensive (NT) and 27 hypertensive (HT) black subjects were kept on a low-sodium diet (30 mmol sodium/d, LS) and on a high-sodium diet (300 mmol sodium/d, HS) for 1 week each. On the last day of each regimen, 24 hour ambulatory blood pressure monitoring was performed.


RESULTS
Eight normotensives were classified as salt-sensitive (SS), all with haptoglobin phenotypes (FeHap) 1,1 or 1,2, and 12 as salt resistant (SR), 5 with FeHap 2,2. Seventeen hypertensives were classified as SS, all with FeHap 1,1 or 1,2, and 11 as SR, 2 with FeHap 2,2. Salt sensitivity criterium was: difference > 5 mmHg of 24 h mean blood pressure from low sodium to high sodium. The pattern of daytime-nighttime blood pressure relationship between LS and HS was only modified (respectively from dipper to non-dipper) in HT-SS, but not in NT-SS, NT-SR and HT-SR. The percentual drop in nighttime mean blood pressure was about 10% in HT-SR and in NT-SR either under LS or HS. In NT-SS, the percentual night-time drop in mean blood pressure was lower than that of NT-RS (i.e. about 7-8%), but it was not different on LS and on HS. In contrast, in HT-SS, the percentual nighttime drop in mean blood pressure on HS (6%) was significantly lower than that on LS (10%, p < 0.01). In the 27 HT, but not in the NT, changes in the nocturnal drop in mean blood pressure induced by salt restriction correlated positively with the degree of salt sensitivity (r = 0.45, p < 0.05).


CONCLUSIONS
In black subjects, the pattern of nighttime-daytime blood pressure relationship appears to be modified from LS to HS diets (or vice-versa) only in SS hypertensive subjects, but neither in NT-SS nor in NT-SS and HT-SR. Only in HT-SS, but not in the other groups, salt restriction shifts the circadian rhythm of blood pressure from a non-dipper to a dipper pattern. We conclude that in black salt-sensitive hypertensives, salt restriction improves the circadian rhythm of blood pressure. This may have important therapeutic consequences on target organ damage associated with non-dipper patterns.
Damasceno
A
A
Faculdade de Medicina, Universidade Eduardo Mondlane, Maputo, Moçambique.
Caupers
P
P
Santos
A
A
Lobo
E
E
Sevene
E
E
Bicho
M
M
Polónia
J
J
D000328:Adult; D000704:Analysis of Variance; D044383:Black People; D001794:Blood Pressure / Q000187:drug effects*; D002940:Circadian Rhythm / Q000187:drug effects*; D018592:Cross-Over Studies; D004562:Electrocardiography; D005260:Female; D006801:Humans; D006973:Hypertension / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage*
D017673:Sodium Chloride, Dietary