Urinary Excretion of Sodium, Potassium, and Chloride, but Not Iodine, Varies by Timing of Collection in a 24-Hour Calibration Study

• Published in: The Journal of nutrition Vol. 143; no. 8; pp. 1276 - 1282
• Main Authors: WANG, Chia-Yih, COGSWELL, Mary E, SEMPOS, Christopher T, GILLESPIE, Cathleen D, BURT, Vicki L, LORIA, Catherine M, CHEN, Te-Ching, PFEIFFER, Christine M, SWANSON, Christine A, CALDWELL, Kathleen L, PERRINE, Cria G, CARRIQUIRY, Alicia L, KIANG LIU
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Nutrition 01.08.2013; Oxford University Press
• Subjects: Adolescent; Adult; Biological and medical sciences; Calibration; Chlorides - urine; Circadian Rhythm; Creatinine - urine; Cross-Sectional Studies; Feeding. Feeding behavior; Female; Follow-Up Studies; Fundamental and applied biological sciences. Psychology; Humans; Iodine - urine; Male; Nutrition Surveys; Potassium - urine; Sodium - urine; Surveys and Questionnaires; Time Factors; Urine Specimen Collection; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Young Adult; Urine; Biological fluid; Excretion; Nutrition; Sodium; Chlorides; Calibration; Timing; Potassium; Iodine
• ISSN: 0022-3166; 1541-6100
• DOI: 10.3945/jn.113.175927

Because of the logistic complexity, excessive respondent burden, and high cost of conducting 24-h urine collections in a national survey, alternative strategies to monitor sodium intake at the population level need to be evaluated. We conducted a calibration study to assess the ability to characterize sodium intake from timed-spot urine samples calibrated to a 24-h urine collection. In this report, we described the overall design and basic results of the study. Adults aged 18-39 y were recruited to collect urine for a 24-h period, placing each void in a separate container. Four timed-spot specimens (morning, afternoon, evening, and overnight) and the 24-h collection were analyzed for sodium, potassium, chloride, creatinine, and iodine. Of 481 eligible persons, 407 (54% female, 48% black) completed a 24-h urine collection. A subsample (n = 133) collected a second 24-h urine 4-11 d later. Mean sodium excretion was 3.54 ± 1.51 g/d for males and 3.09 ± 1.26 g/d for females. Sensitivity analysis excluding those who did not meet the expected creatinine excretion criterion showed the same results. Day-to-day variability for sodium, potassium, chloride, and iodine was observed among those collecting two 24-h urine samples (CV = 16-29% for 24-h urine samples and 21-41% for timed-spot specimens). Among all race-gender groups, overnight specimens had larger volumes (P < 0.01) and lower sodium (P < 0.01 to P = 0.26), potassium (P < 0.01), and chloride (P < 0.01) concentrations compared with other timed-spot urine samples, although the differences were not always significant. Urine creatinine and iodine concentrations did not differ by the timing of collection. The observed day-to-day and diurnal variations in sodium excretion illustrate the importance of accounting for these factors when developing calibration equations from this study.