Effects of sodium intake and diet on racial differences in urinary potassium excretion: Results from the dietary approaches to stop hypertension (DASH)-sodium trial

Background: We previously showed that African Americans excreted less urinary potassium than whites, even while consuming similar diets in the Dietary Approaches to Stop Hypertension (DASH) trial. We hypothesized that a low-sodium diet may eliminate these differences. Study Design: Data from the DASH-Sodium randomized controlled feeding trial were analyzed. Setting & Participants: 412 adults with prehypertension or stage 1 hypertension. Intervention: Random assignment to either a typical American "control" diet (1.7 g [43 mEq] potassium/2,100 kcal/d) or the DASH diet (4.1 g [105 mEq] potassium/2,100 kcal/d). Within each diet, participants received 3 levels of sodium intake in random order for 30 days. Outcomes & Measurements: 24-hour urine samples were analyzed at the end of each period. The primary outcome was urinary potassium excretion. Results: On the DASH diet, African Americans consistently excreted significantly less urinary potassium (mean 24-hour urinary potassium excretion, 2,594 ± 961 mg [66 ± 25 mEq]) than whites (3,412 ± 1,016 mg [87 ± 26 mEq]) at the highest sodium level; adjusted (P < 0.001); this difference was not altered by sodium level (P = 0.6 comparing white to African American difference in urinary potassium excretion on high- vs low-sodium diet). In contrast, there was a smaller but significant white-African American difference in mean daily urinary potassium excretion in participants fed the control/high-sodium diet that was not present in the control/low-sodium diet (adjusted differences of 281 mg [7 mEq]/d vs 20 mg [0.5 mEq]/d, respectively; P = 0.007). Significant interactions were found between race and diet (P < 0.001) and between race and sodium (P = 0.02). Limitations: Single rather than multiple urine collections were available at each time. Lack of stool potassium and sweat potassium values. Conclusions: Racial differences in urinary potassium excretion depend on sodium intake and diet. Our results may help explain the previously documented large variability in urinary potassium excretion.