Due to the inadequate intake of vitamin D as one of the main identified public health problems, an assessment of dietary intake of vitamin D is crucial. The intake can be easily assessed by the food frequency questionnaire (FFQ) which should be developed to be administered among the intended target population and thus validated at the outset. This Master’s thesis examined the suitability of the FFQ as one of the methods for the assessment of the dietary intake of vitamin D. We analyzed a semiquantitative FFQ, which has been filled out by 54 Slovenian adults at the beginning of the study and once again after 6 weeks, as well as a five-day dietary record (DR5) that they had kept during these 6 weeks. In order to assess the validity of the semiquantitative FFQ we compared the results of the semiquantitative FFQ with those of the gold standard method of DR5. In addition to this, we compared a dietary vitamin D intake determined by two semiquantitative FFQs, administered with the test-retest interval of 6 weeks, in order to assess the reproducibility of the semiquantitative FFQ. The assessment of validity and reproducibility was conducted by examining the standard error, median differences and correlations. The results revealed positive correlation that confirms the validity and reproducibility of the questionnaire. The correlation between the FFQs administered two times was stronger than the correlation between the FFQ and DR5. The study confirmed that the results provided by the semiquantitative FFQ are accurate. However, this method could be optimized in the future studies to further improve its reliability. The analyzed semiquantitative FFQ may be adjusted as a simple tool to assess vitamin D intake among the Slovenian adult population.
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