Spot urine and 24-h diet recall estimates of dietary sodium intake from the 2008/09 New Zealand Adult Nutrition Survey: a comparison.

backgroundWe aimed to test the difference between estimates of dietary sodium intake using 24-h diet recall and spot urine collection in a large sample of New Zealand adults.

methodsWe analysed spot urine results, 24-h diet recall, dietary habits questionnaire and anthropometry from a representative sample of 3312 adults aged 15 years and older who participated in the 2008/09 New Zealand Adult Nutrition Survey. Estimates of adult population sodium intake were derived from 24-h diet recall and spot urine sodium using a formula derived from analysis of INTERSALT data. Correlations, limits of agreement and mean difference were calculated for the total sample, and for population subgroups.

resultsEstimated total population 24-h urinary sodium excretion (mean (95% CI)) from spot urine samples was 3035 mg (2990, 3079); 3612 mg (3549, 3674) for men and 2507 mg (2466, 2548) for women. Estimated mean usual daily sodium intake from 24-h diet recall data (excluding salt added at the table) was 2564 mg (2519, 2608); 2849 mg (2779, 2920) for men and 2304 mg (2258, 2350) for women. Correlations between estimates were poor, especially for men, and limits of agreement using Bland-Altman mean difference analysis were wide.

conclusionsThere is a poor agreement between estimates of individual sodium intake from spot urine collection and those from 24-hour diet recall. Although, both 24-hour dietary recall and estimated urinary excretion based on spot urine indicate mean population sodium intake is greater than 2 g, significant differences in mean intake by method deserve further investigation in relation to the gold standard, 24-hour urinary sodium excretion.