Estimating dietary sodium intake in individuals receiving a randomly fluctuating intake.

Previous investigations examining techniques to estimate sodium intake in free-living persons failed to consider a varying intake or were not conducted under circumstances in which the intake was actually known. To examine the utility of 24-hour and nocturnal urine collections as estimation of sodium intake under such conditions, we studied 43 white and black men and women ingesting a known sodium intake for 10 days that was randomly varied daily, with a mean intake of 150 mEq/day + 2 SD (range, 50 to 250 mEq/day). The mean 24-hour sodium excretion (UNaV) per day was and 24-hour UNaV estimated that day's sodium intake accurately for the entire 10 days, the average of several 24-hour collections was required. Nine collections were optimal (r = 0.75). Nocturnal specimens were not helpful; the average of all 10 collections correlated weakly (r = 0.30) with sodium intake. These data suggest that to estimate mean sodium intake accurately in free-living persons, only 24-hour collections are useful, although nocturnal collections are helpful in evaluating compliance with low sodium intake.