Development and validation of a short questionnaire to assess sodium intake

<jats:title>Abstract</jats:title><jats:sec id="S1368980007000146_abs1" sec-type="general"><jats:title>Objectives</jats:title><jats:p>To develop and validate a short food-frequency questionnaire to assess habitual dietary salt intake in South Africans and to allow classification of individuals according to intakes above or below the maximum recommended intake of 6 g salt day<jats:sup>−1</jats:sup>.</jats:p></jats:sec><jats:sec id="S1368980007000146_abs2" sec-type="general"><jats:title>Design</jats:title><jats:p>Cross-sectional validation study in 324 conveniently sampled men and women.</jats:p></jats:sec><jats:sec id="S1368980007000146_abs3" sec-type="methods"><jats:title>Methods</jats:title><jats:p>Repeated 24-hour urinary Na values and 24-hour dietary recalls were obtained on three occasions. Food items consumed by >5% of the sample and which contributed ≥50 mg Na serving<jats:sup>−1</jats:sup>were included in the questionnaire in 42 categories. A scoring system was devised, based on Na content of one index food per category and frequency of consumption.</jats:p></jats:sec><jats:sec id="S1368980007000146_abs4" sec-type="results"><jats:title>Results</jats:title><jats:p>Positive correlations were found between Na content of 35 of the 42 food categories in the questionnaire and total Na intake, calculated from 24-hour recall data. Total Na content of the questionnaire was associated with Na estimations from 24-hour recall data (<jats:italic>r</jats:italic>= 0.750;<jats:italic>P</jats:italic>< 0.0001;<jats:italic>n</jats:italic>= 328) and urinary Na (<jats:italic>r</jats:italic>= 0.152;<jats:italic>P</jats:italic>= 0.0105;<jats:italic>n</jats:italic>= 284). Urinary Na was higher for subjects in tertile 3 than tertile 1 of questionnaire Na content (<jats:italic>P</jats:italic>< 0.05). Questionnaire Na content of <2400 and ≥2400 mg day<jats:sup>−1</jats:sup>equated to a reference cut-off score of 48 and corresponded to mean (standard deviation) urinary Na values of 145 (68) and 176 (99) mmol day<jats:sup>−1</jats:sup>, respectively (<jats:italic>P</jats:italic>< 0.05). Sensitivity and specificity against urinary Na ≥100 and <100 mmol day<jats:sup>−1</jats:sup>was 12.4% and 93.9%, respectively.</jats:p></jats:sec><jats:sec id="S1368980007000146_abs5" sec-type="conclusion"><jats:title>Conclusion</jats:title><jats:p>A 42-item food-frequency questionnaire has been shown to have content-, construct- and criterion-related validity, as well as internal consistency, with regard to categorising individuals according to their habitual salt intake; however, the devised scoring system needs to show improved sensitivity.</jats:p></jats:sec>