Single 24-hour urine collection does not suffice to estimate an individual’s sodium intake
Use of a Single Baseline Versus Multi-Year 24-Hour Urine Collections for Estimation of Long-Term Sodium Intake and Associated Cardiovascular and Renal RiskLiterature - Olde Engberink RHG, van den Hoek TC, van Noordenne ND, et al., - Circulation. 2017; Originally published June 27, 2017. https://doi.org/10.1161/CIRCULATIONAHA.117.029028
- Average 24-hour sodium excretion at baseline was 3.9±1.0 grams (169±74 mmol).
- Average 24-hour urine sodium excretion showed similar results between a single baseline measurement and follow-up measurements at 1, 5 or 15 years (P=0.88).
- Significant intra-individual changes in 24-hour urinary sodium excretion were observed over time. In most subjects, estimated sodium intake using a single baseline measurement differed at least 0.4 gram sodium (17 mmol sodium, 1 gram of salt) from the 1-year (71%), 5-year (72%) or 15-year (75%) results. In 49%, 50% and 52%, respectively, of the subjects the difference was even 0.8 grams of sodium.
- Tertile classification changed in 45%, 49% and 50% of the 1-year, 5-year and 15-year measurements respectively, as compared with a single baseline measurement.
- Based on a single measurement for sodium intake estimation, high 24-hour sodium excretion was not associated with an increased risk for the composite of CV events and mortality, when compared with low sodium intake (HR: 1.09, 95%CI: 0.61-1.95).
- In 24-hour sodium excretion measurements obtained within 1 year or within 5 years after baseline, high sodium excretion was associated with a higher risk for CV events and death (1-year: HR: 1.80, 95%CI: 1.03-3.13, 5-years HR: 1.73, 95%CI: 1.00-2.99). Hazards for CV events and death of long-term estimates were up to 85% different from baseline estimates.
- Long-term estimates of hazard for renal outcome were up to 47% different from baseline single 24-hour urine excretion data. Inconsistencies were even larger when data were analyzed separately for those with and those without primary kidney disease.
This study shows that, on a population level, a single baseline measurement and repetitive follow-up 24-hour urine sodium measurements lead to similar estimates of sodium intake. Estimations of individual sodium intake, however, differ significantly. This affected the association between sodium intake and long-term outcomes.
These data indicate that a single 24-hour urine sodium collection can be used to estimate average sodium intake in a population, but is imprecise for estimation of long-term individual sodium intake, and thus inadequate to study the relation between sodium intake and long-term CV or renal outcome.
Imprecise estimation of sodium intake at baseline has consequences for classification of subjects as low, moderate or high sodium consumers. Only when 1- and 5-year estimates were used, a positive correlation between sodium intake and long term CV risks was seen.