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(Hypertension. 2008;51:891.)
© 2008 American Heart Association, Inc.

Original Articles

Nighttime Blood Pressure and Nocturnal Dipping Are Associated With Daytime Urinary Sodium Excretion in African Subjects

Lise Bankir; Murielle Bochud; Marc Maillard; Pascal Bovet; Anne Gabriel; Michel Burnier

From the INSERM Unité 872 and Université Paris V-René Descartes (L.B.), Centre de Recherche des Cordeliers, Paris, France; Institut de Médecine Sociale et Préventive (M.B., P.B.), Lausanne, Switzerland; Division of Nephrology (M.M., M.B.), Centre Universitaire Hospitalier Vaudois, Lausanne, Switzerland; Ministry of Health (P.B., A.G.), Republic of Seychelles.

Correspondence to Michel Burnier, Division of Nephrology and Hypertension Consultation, Centre Universitaire Hospitalier Vaudois, Rue du Bugnon, 17, 1011 Lausanne, Switzerland. E-mail michel.burnier{at}chuv.ch

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.

Key Words: circadian rhythm • glomerular filtration rate • potassium • humans • families

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