Reliability and validity of a semi-quantitative FFQ for sodium intake in low-income and low-literacy Brazilian hypertensive subjects.

OBJECTIVE To assess the reliability and validity of an FFQ to evaluate dietary patterns of Na consumption among low-income and low-literacy Brazilian hypertensive subjects. DESIGN The initial FFQ was submitted to content analysis with the pre-test administered to fifteen subjects. Reliability was evaluated according to the reproducibility criterion, with interviewer administration of the FFQ twice within a 15 d interval. Validity was assessed against a 24 h recall (132 subjects), a 3 d diet record (121 subjects) and a biomarker (24 h urinary Na; 121 subjects). To test the correlation with the biomarker, discretionary salt was added to the FFQ Na values. SETTING A large urban teaching hospital in south-eastern Brazil. SUBJECTS The study was based on 132 randomly selected subjects (eighty-three women and forty-nine men) aged 18 to 85 years. RESULTS Kappa coefficients ranged from 0.79 to 0.98, confirming the reproducibility of the FFQ. There was no correlation between urinary Na excretion, the FFQ and the 24 h recall for the general sample, although significant correlations had been observed when methods were summed up (24 h recall + discretionary salt + FFQ; 0.32, P = 0.01). The addition of discretionary salt significantly improved the biomarker-based FFQ validity, with correlation coefficients varying from 0.19 (general sample) to 0.31 (female sub-sample). CONCLUSIONS The developed FFQ demonstrated satisfactory evidence of validity and reliability and can be used as an important complementary tool for the evaluation of Na intake among Brazilian hypertensive subjects.