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

ABSTRACT

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.