Racial differences in sodium and potassium retention in response to dietary salt in female adolescents

The purpose of this study was to determine the effect of dietary salt on sodium and potassium handling in adolescent black and white females. To achieve this objective a metabolic, randomized order, crossover study of low and high sodium diet was performed for 3 weeks. Preliminary studies in sweat collection were performed in adults to determine the best methodology to be used in our metabolic study with adolescents and to quantitatively measure sweat sodium loss while on a low sodium diet. Twenty-four hour whole body sweat collection was the preferred method chosen. Mineral content of daily diet, urine, and fecal samples, as well as sweat by 3 different methods: 24-h whole body, 30-min arm bag, and 30-min patch were measured during each balance period in adolescents. Renal biomarkers, blood pressure, and weight were also measured. No racial differences were detected in whole body sweat mineral loss; however, blacks excreted significantly less urinary sodium with the high sodium diet, which resulted in higher sodium retention, and less urinary potassium at either salt intake compared to whites. Plasma aldosterone and plasma renin activity at the end of the study periods were also suppressed in blacks with the high sodium diet, consistent with the urine data. Blood pressure did not increase with the high sodium diet in blacks but it decreased with the low sodium diet. In conclusion, a higher positive sodium balance, suppressed plasma renin activity, and lower aldosterone levels were observed in the black compared to the white girls while consuming a high salt diet, indicating renal sodium retention.