Individual variation in urinary sodium excretion among adolescent girls on a fixed intake

According to traditional understanding of sodium homeostasis, nearly all of daily sodium intake is excreted in urine, with intraindividual variability attributed to variability in dietary sodium intake and urine collection errors. To analyze the variability of urinary sodium in excretion from a balance study with fixed sodium intakes. Daily 24-h urine collections were assessed for sodium, potassium, and creatinine in 22 black and 13 white adolescent girls (11-15 year, BMI 15-29 kg/m) in a randomized, crossover design with controlled diets containing either low (57 mmol/day) or high (167 mmol/day) sodium, each fed for 3 weeks. Coefficient of variation analysis indicated higher variation in urinary sodium excretion about the mean on low (vs high) sodium (40 vs 32%, P = 0.02) and in black (vs white) girls (42 vs 30%, P