Supplementary Material for: Correcting for plasma aldosterone improves the accuracy of repeated timed urine sampling for estimation of dietary sodium intake

Introduction
Long-term sodium balance studies show that sodium can be temporarily stored and released in tissues, mediated by circaseptan rhythms of aldosterone and cortisol. This complicates the reliability of a single 24-hour urine collection to estimate individual sodium intake. We investigated whether repeated timed urine collection with and without correction for plasma aldosterone is a more accurate alternative for estimating daily sodium intake.
Methods
We conducted a post-hoc analysis of a metabolic ward study in which 16 healthy male adults consumed a diet with a fixed sodium content (50 or 200 mmol/day) for 7 days. Each day, urine was collected in 4 intervals (7:00-13:00h, 13:00-19:00h, 19:00-23:00h and 23:00-07:00h). Plasma aldosterone was measured at 6:30h, 12:30h and 18:30h. Sodium intakes were estimated by various formulas using 3 timed urines of day 5 to 7.
Results
During a 200-mmol daily sodium intake, sodium intake estimates based on three repeated timed urine samples and the Toft equation differed 10 [IQR 3-14], 8 [6-19], 36 [16-49] and 20 [10-43] mmol from the actual intake for intervals 7:00-13:00h, 13:00-19:00h, 19:00-23:00h, 23:00-07:00h, respectively. These measurements did not significantly differ from a single 24-hour urine (20 [12-55] mmol). During a 50-mmol daily sodium intake, repeated timed urine collection performed worse than a single 24-hour urine collection. On both diets, correction for plasma aldosterone increased accuracy and sodium intake estimates were significantly more accurate than a single 24-hour urine.
Conclusion
In a controlled environment, repeated timed urine collection corrected for plasma aldosterone is more accurate than a single 24-hour urine collection.

引言（Introduction）
长期钠平衡研究表明，钠可在组织中暂时储存与释放，该过程受醛固酮与皮质醇的七日节律调控。这使得单份24小时尿液收集用于估算个体钠摄入量的可靠性大打折扣。本研究旨在探讨，重复定时尿液收集（结合或不结合血浆醛固酮校正）能否作为更精准的日常钠摄入量估算方案。

方法（Methods）
本研究对一项代谢病房研究开展事后分析：16名健康成年男性连续7天食用钠含量固定（50或200 mmol/日）的膳食。每日分4个时段收集尿液：7:00-13:00、13:00-19:00、19:00-23:00及23:00-07:00。分别于6:30、12:30及18:30测定血浆醛固酮水平。研究人员采用多种公式，通过第5至7天的3份定时尿液样本估算钠摄入量。

结果（Results）
当每日钠摄入量为200 mmol时，基于3份重复定时尿液样本与Toft公式的钠摄入量估算值，在7:00-13:00、13:00-19:00、19:00-23:00及23:00-07:00四个时段下，与实际摄入量的差值分别为10 [四分位距（Interquartile Range，IQR）3-14]、8 [IQR 6-19]、36 [IQR 16-49]及20 [IQR 10-43] mmol。该估算结果与单份24小时尿液收集的估算值（20 [IQR 12-55] mmol）无显著差异。当每日钠摄入量为50 mmol时，重复定时尿液收集的表现劣于单份24小时尿液收集。在两种膳食方案下，结合血浆醛固酮校正均可提升估算准确性，且钠摄入量估算值的精准度显著优于单份24小时尿液收集方案。

结论（Conclusion）
在受控环境中，结合血浆醛固酮校正的重复定时尿液收集方案，其精准度优于单份24小时尿液收集。