Introduction: The intake of salt (NaCl) is a concern for patients who form calcium stones as it expands extracellular volume and enhances renal calcium excretion. The 24-hour urinary excretion of sodium (UNa) correlates directly with dietary salt intake and is modifiable with medical nutrition therapy. To assess the effectiveness of nutritional recommendations to lower salt intake, we measured the reduction of UNa among patients with high UNa in their initial 24-hour urines.
Methods: An IRB-approved prospectively maintained database of 24-hour urine results from patients with nephrolithiasis at a referral center was retrospectively analyzed for all patients between 2009 to 2019 with two 24-hour urine results within 2 to 18 months. Age, BMI, gender, race, ethnicity, socioeconomic status (SES), and comorbidities were included in univariate and multivariate analyses. Exclusion criteria included age <18 and a stone prevention clinic visit prior to the first 24-hour urine.
Results: Of patients meeting inclusion criteria (n=1,137), 272 had high UNa in their initial 24-hour urine collections (>200 mmol/day). Of these, 129 (47%) achieved UNa <200 mmol/day at follow-up. On multivariate analysis women were significantly more likely than men to reduce their UNa (univariate p=0.06, multivariate p=0.005, beta=0.33). Patients with lower BMI were also more likely to reduce UNa (univariate p<0.01, multivariate p<0.01, beta=1.10). Patients with diabetes reduced UNa when a univariate statistical approach was used (p=0.02), but this association disappeared with multivariate analysis (p=0.22). Age, race, ethnicity, SES, hypertension, gout, chronic urinary tract infection, and chronic kidney disease were all found to be not significantly associated with reduction of UNa in both univariate and multivariate analyses.
Conclusions: Women and patients with lower BMI were more likely to reduce UNa to <200 mmol after receiving medical nutrition therapy at our referral center. Future work should be aimed at identifying the successful strategies for lowering dietary salt intake employed by women and patients with lower BMI and the barriers to such in other patient groups. Source of