Reliable Quantification of the Potential for Equations Based on Spot Urine Samples to Estimate Population Salt Intake: Protocol for a Systematic Review and Meta-Analysis

Effects of a reduced-sodium added-potassium salt substitute on blood pressure in rural Indian hypertensive patients: a randomized, double-blind, controlled trial

BACKGROUND

High salt intake is a major modifiable risk factor of hypertension which is prevalent in India. It is not yet clear if salt substitutes reduce blood pressure (BP) among Indian hypertensive patients.

OBJECTIVES

Examine the acceptability, usage, and BP effects of a reduced-sodium and added-potassium salt substitute among hypertensive patients.

METHODS

We enrolled 502 participants with hypertension (aged 61.6 ± 12.0 y, 58.8% women) from 7 villages in rural India. Participants were randomly assigned to receive either regular salt (100% sodium chloride) or the salt substitute (70% sodium chloride/30% potassium chloride blend), and advised to replace all home salt use. The primary outcome was the change in systolic BP (SBP) from baseline to 3 mo comparing the salt substitute and regular salt groups. Secondary outcomes included the change in diastolic BP (DBP), 24-h urinary biomarkers, and self-reported use and satisfaction with the study salt provided.

RESULTS

A total of 494 (98%) participants completed 1 mo and 476 (95%) participants completed the 3-mo follow-up. At 3 mo, the salt substitute intervention significantly decreased the average SBP by 4.6 mmHg (95% CI: 3.0, 6.2, P < 0.001) and DBP by 1.1 mmHg (95% CI: 0.2, 2.1 mmHg, P = 0.02). There was a significant increase in 24-h urinary potassium excretion in the salt substitute group by 0.24 g/d (95% CI: 0.12, 0.35 g/d, P < 0.001) and a decrease in the urinary sodium to potassium ratio by 0.71 (95% CI: 0.55, 0.87, P < 0.0001) compared with the control group. Participants reported that they used the study salt nearly every day of the week (mean ± SD, 6.3 ± 1.8 d) and rated the taste of the study salts similarly.

CONCLUSION

The reduced-sodium added-potassium salt led to a substantial reduction in SBP in hypertensive patients, supporting salt substitution as an effective, low-cost intervention for BP lowering in rural India. This trial was registered at clinicaltrials.gov as NCT03909659.

Urine Spot Samples Can Be Used to Estimate 24-Hour Urinary Sodium Excretion in Children

Background

The gold standard to assess salt intake is 24-h urine collections. Use of a urine spot sample can be a simpler alternative, especially when the goal is to assess sodium intake at the population level. Several equations to estimate 24-h urinary sodium excretion from urine spot samples have been tested in adults, but not in children.

Objective

The objective of this study was to assess the ability of several equations and urine spot samples to estimate 24-h urinary sodium excretion in children.

Methods

A cross-sectional study of children between 6 and 16 y of age was conducted. Each child collected one 24-h urine sample and 3 timed urine spot samples, i.e., evening (last void before going to bed), overnight (first void in the morning), and morning (second void in the morning). Eight equations (i.e., Kawasaki, Tanaka, Remer, Mage, Brown with and without potassium, Toft, and Meng) were used to estimate 24-h urinary sodium excretion. The estimates from the different spot samples and equations were compared with the measured excretion through the use of several statistics.

Results

Among the 101 children recruited, 86 had a complete 24-h urine collection and were included in the analysis (mean age: 10.5 y). The mean measured 24-h urinary sodium excretion was 2.5 g (range: 0.8-6.4 g). The different spot samples and equations provided highly heterogeneous estimates of the 24-h urinary sodium excretion. The overnight spot samples with the Tanaka and Brown equations provided the most accurate estimates (mean bias: -0.20 to -0.12 g; correlation: 0.48-0.53; precision: 69.7-76.5%; sensitivity: 76.9-81.6%; specificity: 66.7%; and misclassification: 23.0-27.7%). The other equations, irrespective of the timing of the spot, provided less accurate estimates.

Conclusions

Urine spot samples, with selected equations, might provide accurate estimates of the 24-h sodium excretion in children at a population level. At an individual level, they could be used to identify children with high sodium excretion. This study was registered at clinicaltrials.gov as NCT02900261.