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Hypertension. 2015 Oct;66(4):850-7. doi: 10.1161/HYPERTENSIONAHA.115.05851. Epub 2015 Aug 10.

Agreement between 24-hour salt ingestion and sodium excretion in a controlled environment.

Author information

1
From the Interdisciplinary Center for Clinical Research (K.L., N.R., U.G., J.T.), Department of Nephrology and Hypertension (A.D., K.-U.E., J.T.), and Department of Pediatrics (M.R.), Friedrich-Alexander-University, Erlangen-Nürnberg, Germany; Experimental and Clinical Research Center, an institutional cooperation between the Charité Medical Faculty and the Max-Delbrück Center for Molecular Medicine, Berlin, Germany (N.R., F.C.L.); Unit for Experimental Psychiatry, Division of Sleep and Chronobiology, Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia (M.B., D.F.D.); Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany (L.B., B.J.); State Scientific Center of Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia (A.A., I.L., V.B., B.M., G.V.); Fresenius Medical Care-D GmbH, Bad Homburg, Germany (P.W., J.V.); Center for Space Medicine, Institute of Physiology, Charité - University Clinic Berlin, Berlin, Germany (K.K.); Department of Biostatistics, Coordination Center for Clinical Trials, Charité University Medicine Berlin, Berlin, Germany (A.K.); and Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN (F.C.L., J.T.).
2
From the Interdisciplinary Center for Clinical Research (K.L., N.R., U.G., J.T.), Department of Nephrology and Hypertension (A.D., K.-U.E., J.T.), and Department of Pediatrics (M.R.), Friedrich-Alexander-University, Erlangen-Nürnberg, Germany; Experimental and Clinical Research Center, an institutional cooperation between the Charité Medical Faculty and the Max-Delbrück Center for Molecular Medicine, Berlin, Germany (N.R., F.C.L.); Unit for Experimental Psychiatry, Division of Sleep and Chronobiology, Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia (M.B., D.F.D.); Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany (L.B., B.J.); State Scientific Center of Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia (A.A., I.L., V.B., B.M., G.V.); Fresenius Medical Care-D GmbH, Bad Homburg, Germany (P.W., J.V.); Center for Space Medicine, Institute of Physiology, Charité - University Clinic Berlin, Berlin, Germany (K.K.); Department of Biostatistics, Coordination Center for Clinical Trials, Charité University Medicine Berlin, Berlin, Germany (A.K.); and Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN (F.C.L., J.T.). jens.m.titze@Vanderbilt.Edu friedrich.luft@charite.de.

Abstract

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.

KEYWORDS:

dietary; hypertension; salt; sodium; urine specimen collection

PMID:
26259596
PMCID:
PMC4567387
DOI:
10.1161/HYPERTENSIONAHA.115.05851
[Indexed for MEDLINE]
Free PMC Article

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