Salt and dipping BP.

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Hypertension. 2008 Apr;51(4):891-8. Epub 2008 Mar 3.



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Comment in:

Hypertension. 2008 Apr;51(4):827-8.

Hypertension. 2008 Aug;52(2):e10; author reply e11.

Nighttime blood pressure and nocturnal dipping are associated with

daytime urinary sodium excretion in African subjects.

Bankir L, Bochud M, Maillard M, Bovet P, A, Burnier M.

INSERM Unité 872 and Université Paris V-René Descartes, Centre de

Recherche des Cordeliers, Paris, France.

Blood pressure (BP) follows a circadian rhythm, with 10% to 15% lower

values during nighttime than during daytime. The absence of a

nocturnal BP decrease (dipping) is associated with target organ

damage, but the determinants of dipping are poorly understood. We

assessed whether the nighttime BP and the dipping are associated with

the circadian pattern of sodium excretion. Ambulatory BP and daytime

and nighttime urinary electrolyte excretion were measured

simultaneously in 325 individuals of African descent from 73

families. When divided into sex-specific tertiles of day:night ratios

of urinary sodium excretion rate, subjects in tertile 1 (with the

lowest ratio) were 6.5 years older and had a 9.8-mm Hg higher

nighttime systolic BP (SBP) and a 23% lower SBP dipping (expressed in

percentage of day value) compared with subjects in tertile 3 (P for

trend <0.01). After adjustment for age, the SBP difference across

tertiles decreased to 5.4 mm Hg (P=0.002), and the SBP dipping

difference decreased to 17% (P=0.05). A similar trend across tertiles

was found with diastolic BP. In multivariate analyses, daytime

urinary sodium and potassium concentrations were independently

associated with nighttime SBP and SBP dipping (P<0.05 for each).

These data, based on a large number of subjects, suggest that the

capacity to excrete sodium during daytime is a significant

determinant of nocturnal BP and dipping. This observation may help us

to understand the pathophysiology and clinical consequences of

nighttime BP and to develop therapeutic strategies to normalize the

dipping profile in hypertensive patients.