Sex

We have made several observations that comple-ment those of Liu et al.1- ' on the utility of overnight urine collections for estimation of sodium intake. Six children (mean age 9.5 ± 1.1 years) were studied for 5 days in the metabolic ward of our hospital after being placed on a constant diet of 100 mmoles of sodium and 75 mmoles of potassium. The results of timed urine collections are shown in table 1. The correlation of overnight with daytime sodium excretion was r =-0.11, t =-0.22 (r = 0.08, 0.76 for potassium and creatinine). Another group of 12 free-living children (mean age 7.4 ±.6 years) provided timed 10-hour overnight and 14-hour daytime urine collections before, during, and after being placed on a sodium-restricted diet (table 2). It was of interest that both daytime and 24-hour urine sodium excretion decreased significantly but overnight excretion remained constant. The fall in daytime creatinine excretion could reflect incomplete collections or time changes in renal function. Three-day food records showed declining intake.' Further studies of the ability of various measures of sodium intake to detect change should be undertaken