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

Objective: The 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. Design: In 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. Setting: Three major universities in Serbia. Subjects: Healthy young women (n 422) aged 18-35 years. Results: The WRH-FFQ estimate of vitamin D intake for all participants was 4.0 (SD 3.3) mu g/d and 3.1 (SD 2.3) mu g/d for the subgroup. Bland-Altman plots for these intakes showed high agreement. Validity coefficients for the FFQ, 24 h recall and biomarker were. rho(QI) = 0.847 (95 % CI 0.564, 0.928), rho(RI) = 0.810 (95 % CI 0.537, 0.997) and rho(BI) = 0.499 (95 % CI 0.190, 0.840), while the correlation coefficients were 0.686, 0.422 and 0.404. Conclusions: The 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.