Validation of food frequency questionnaire to assess folate intake status in breast cancer patients

Inadequate folate intake could be associated with increased breast cancer risk. The aim of the present study was to assess the folate intake by designed Food Frequency Questionnaire (FFQ) using plasma folate concentration. This analytic cross-sectional study was conducted to evaluate the validity of the semi-quantitative FFQ (136 items) in 152 women with confirmed breast malignancy aged between 35 - 85 years old.. Folate plasma level was assessed by means of automated electrochemiluminescence. The Pearson and partial correlation coefficients were performed between the plasma level of folate and crude, total and energy-adjusted (residual) folate intakes. Area under ROC curve (AUC), sensitivity, specificity, positive and negative predictive values and odds ratio were fulfilled in two models in order to achieve validity assessment. The folate plasma level was significantly correlated with total intake of vegetables, bread and cereal groups (p=0.001) and also with total intake of fruits (p=0.001) and dairy products (p=0.026). After adjusting for confounders, the folate plasma levels were correlated significantly with daily (β=0.39), and residual (β=0.41) folate intake levels (p=0.001). The area under ROC curves in model I (folate plasma level <5.9 ng/ml) was 0.74 (95%CI=0.63-0.85) and for model II (folate plasma level <10.0 ng/ml) was estimated as 0.61(95%CI= 0.51- 0.71). Model I indicated more appropriate predictive value (p=0.001) of folate intake assessment via FFQ. The results of this study showed that FFQ described in this study could be a valid and appropriate tool for assessing folate intake status in dietary content of breast cancer patients and also could be representative and valid for assessing the folate rich-food intake status.