Twenty four-hour urinary excretion of sodium, potassium and urea in Japanese children.

The general profile of sodium and potassium intake during childhood was studied by the analysis of excretion in 24-hr urine samples collected from 119 healthy Japanese children at the ages of 1 to 18 years. In order to analyze sodium and potassium excretion under the changing body size and diet during growth, sodium and potassium were further expressed as values relative to creatinine and urea, as the reflection of body muscle mass and protein intake, respectively. Both of sodium and potassium (mEq/24-hr) increased significantly with age. Sodium/creatinine and potassium/creatinine, however, decreased significantly with age, suggesting that the increase in muscle mass exceed that in dietary intakes of sodium and potassium. When urinary sodium and potassium were expressed as ratios to urea-N, sodium/urea-N increased, but potassium/urea-N decreased with age. Sodium/potassium ratio increased with age. Thus, the results suggest that, in the given population of Japanese children, the amount of sodium per calorie or per protein in the diet increase, and that of potassium decrease with age.