Validity of an FFQ assessing the vitamin D intake of young Serbian women living in a region without food fortification: the method of triads model

Abstract

AbstractObjectiveThe objective of the present study was to examine the external validity of an FFQ designed to estimate dietary vitamin D intake compared with a plasma biomarker and three repeated 24 h dietary recalls in women of reproductive age in Serbia, where there is no exposure to food fortified with vitamin D. The method of triads was applied.DesignIn a cross-sectional study, 422 women completed the Women and Reproductive Health FFQ (WRH-FFQ) during the winter months. From a representative subgroup (n 44), three 24 h dietary recalls and anthropometric parameters were collected as well as a fasting blood sample for vitamin D biomarker analyses. Correlation coefficients were calculated between each of the dietary methods. Validity coefficients, as a correlation between the measured and estimated ‘true’ exposure, were calculated using the method of triads. Bland–Altman plots were also constructed.SettingThree major universities in Serbia.SubjectsHealthy young women (n 422) aged 18–35 years.ResultsThe WRH-FFQ estimate of vitamin D intake for all participants was 4·0 (sd 3·3) µg/d and 3·1 (sd 2·3) µg/d for the subgroup. Bland–Altman plots for these intakes showed high agreement. Validity coefficients for the FFQ, 24 h recall and biomarker were ρQI=0·847 (95 % CI 0·564, 0·928), ρRI=0·810 (95 % CI 0·537, 0·997) and ρBI=0·499 (95 % CI 0·190, 0·840), while the correlation coefficients were 0·686, 0·422 and 0·404.ConclusionsThe FFQ applied in the present study is a valid tool for assessing dietary vitamin D intake in women living in Serbia, a region without mandatory vitamin D food fortification.