Use of a Single Baseline Versus Multi-Year 24-Hour Urine Collections for Estimation of Long-Term Sodium Intake and Associated Cardiovascular and Renal Risk
Background—A decrease in sodium intake has been shown to lower blood pressure, but data from cohort studies on the association with cardiovascular and renal outcomes are inconsistent. In these studies sodium intake was often estimated using a single baseline measurements, which may be inaccurate considering day-to-day changes in sodium intake and sodium excretion. We compared the effects of single versus repetitive follow-up 24-hour urine samples on the relation between sodium intake and long-term cardiorenal outcomes.
Methods—We selected adult subjects with an eGFR >60 mL/min, an outpatient 24-hour urine sample between 1998-1999 and at least 1 collection during a 17-year follow-up. Sodium intake was estimated using a single baseline collection and the average of samples that were collected during a 1, 5 and 15-year follow-up. We used Cox-regression analysis and the landmark approach to investigate the relation between sodium intake and cardiovascular (cardiovascular events or mortality) and renal outcome (end-stage renal disease (ESRD): dialysis, transplantation and >60% eGFR decline, or mortality).
Results—We included 574 subjects with 9,776 24-hour urine samples. Average age was 47 years and 46% were male. Median follow-up was 16.2 years. Average 24-hour sodium excretion, ranging from 3.8- 3.9 gram (165-170 mmol), was equal among all methods (p=0.88). However, relative to a single baseline measurement, 50% of the subjects had a >0.8 gram sodium (>34 mmol) difference in sodium intake with long-term estimations. As a result, 45%, 49% and 50% of all subjects switched between tertiles of sodium intake when using 1, 5, or 15-year averages, respectively. Consequently, hazard ratios for cardiorenal outcome changed up to 85% when using sodium intake estimations from short-term (1-year) and long-term (5-year) follow-up, instead of baseline estimations.
Conclusions—Relative to a single baseline 24-hour sodium measurement, the use of subsequent 24-hour urine samples resulted in different estimations of an individual's sodium intake, while population averages remained similar. This had significant consequences for the association between sodium intake and long-term cardiovascular and renal outcome.
- Received May 25, 2017.
- Accepted June 8, 2017.