Objectives: 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.
Design: Cross-sectional validation study in 324 conveniently sampled men and women.
Methods: Repeated 24-hr urinary Na values and 24-hr dietary recalls were obtained on three occasions. Food items consumed by > 5% sample and which contributed e 50 mg Na/serving 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.
Results: Positive correlations were found between Na content of 35 of the 42 food categories in the questionnaire and total Na intake, calculated from 24-hr recall data. Total Na content of the questionnaire was associated with Na estimations from 24-hr recall data (r = 0.750; P <0.0001; N = 328) and urinary Na (r = 0.152; P = 0.0105; N = 284). Urinary Na was higher for subjects in tertile 3 than tertile 1 of questionnaire Na content (P<0.05). Questionnaire Na content of < and e 2 400 mg/day equated to a reference cut-off score of 48 and corresponded to urinary Na values of 145 (68) and 176 (99) mmol/day, respectively (P<0.05). Sensitivity and specificity against urinary Na e and < 100 mmol/day was 14.2 % and 92.4%, respectively.
Conclusion: 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.