Agreement Between 24-Hour Salt Ingestion and Sodium Excretion in a Controlled Environment

• Published in: Hypertension (Dallas, Tex. 1979) Vol. 66; no. 4; pp. 850 - 857
• Main Authors: Lerchl, Kathrin, Rakova, Natalia, Dahlmann, Anke, Rauh, Manfred, Goller, Ulrike, Basner, Mathias, Dinges, David F, Beck, Luis, Agureev, Alexander, Larina, Irina, Baranov, Victor, Morukov, Boris, Eckardt, Kai-Uwe, Vassilieva, Galina, Wabel, Peter, Vienken, Jörg, Kirsch, Karl, Johannes, Bernd, Krannich, Alexander, Luft, Friedrich C, Titze, Jens
• Format: Journal Article
• Language: English
• Published: United States American Heart Association, Inc 01-10-2015
• Subjects: Adult; Blood Pressure - physiology; Circadian Rhythm - physiology; Environment, Controlled; Follow-Up Studies; Humans; Hypertension - physiopathology; Hypertension - urine; Male; Reference Values; Sodium - urine; Sodium Chloride, Dietary - administration & dosage; Urine Specimen Collection; sodium; urine specimen collection; salt; dietary; hypertension
• ISSN: 0194-911X; 1524-4563
• DOI: 10.1161/HYPERTENSIONAHA.115.05851

Accurately collected 24-hour urine collections are presumed to be valid for estimating salt intake in individuals. We performed 2 independent ultralong-term salt balance studies lasting 105 (4 men) and 205 (6 men) days in 10 men simulating a flight to Mars. We controlled dietary intake of all constituents for months at salt intakes of 12, 9, and 6 g/d and collected all urine. The subjects’ daily menus consisted of 27 279 individual servings, of which 83.0% were completely consumed, 16.5% completely rejected, and 0.5% incompletely consumed. Urinary recovery of dietary salt was 92% of recorded intake, indicating long-term steady-state sodium balance in both studies. Even at fixed salt intake, 24-hour urine collection for sodium excretion (UNaV) showed infradian rhythmicity. We defined a ±25 mmol deviation from the average difference between recorded sodium intake and UNaV as the prediction interval to accurately classify a 3-g difference in salt intake. Because of the biological variability in UNaV, only every other daily urine sample correctly classified a 3-g difference in salt intake (49%). By increasing the observations to 3 consecutive 24-hour collections and sodium intakes, classification accuracy improved to 75%. Collecting seven 24-hour urines and sodium intake samples improved classification accuracy to 92%. We conclude that single 24-hour urine collections at intakes ranging from 6 to 12 g salt per day were not suitable to detect a 3-g difference in individual salt intake. Repeated measurements of 24-hour UNaV improve precision. This knowledge could be relevant to patient care and the conduct of intervention trials.