Development of a food frequency questionnaire to determine vitamin kintake in anticoagulated patients: a pilot study

Our aim was to develop a food frequency questionnaire (FFQ) to estimate vitamin K intake in patients receiving warfarin. We conducted a cross-sectional study. The FFQ was designed based on a literature review, and included foods containing >= 5 mu g/100 g consumed by the study group. The correlation between the intake of vitamin K estimated by the questionnaire and habitual intake measured by two 24-hour dietary recalls was assessed, as well as correlations between FFQ, International Normalized Ratio (INR) and serum vitamin K levels. The mean intake of vitamin K, estimated by the FFQ, was 112.6 +/- 82.7 mu g/day, and the habitual dietary intake estimated by 24-hour dietary recalls was 85.1 +/- 75.5 mu g/ day, with a significant correlation between both methods (r= 0.756; p< 0.001). There was no correlation between FFQ and INR (r= 0.054; p= 0.716), or between FFQ and serum vitamin K (r= -0.005; p= 0.982). The strong correlation between vitamin K intake measured by FFQ and habitual dietary intake measured by 24-hour dietary recalls suggests that the FFQ can be used to estimate vitamin K intake.