Development and Validity of a Food Frequency Questionnaire for Assessing Vitamin C Intake in Turkish Adults

English (OpenAlex)

Objective: This study aimed to evaluate the validity of a food frequency questionnaire (FFQ) developed to determine vitamin C intake. Material and Methods: This research was carried out at Istanbul University Faculty of Dentistry between October 2017 and May 2018. There were 75 individuals in this study, who were 18-65 years old. In order to determine the level of vitamin C intake of individuals, a FFQ was formed which contains the consumption frequency and the amount of consumption of 83 foods and its language is Turkish. After the determination of the plasma ascorbic acid level (PAAL) of the individuals, the validity of the questionnaire was examined by Spearman correlation test, Bland Altman plot and kappa statistics. All statistical analysis were performed using the IBM SPSS Statistics 20 Software and statistically significant differences were determined using a p value <0.05. Results: A total of 75 people (31 male and 44 female) participated in this study, and the mean age was 35.69±10.35 years. The median PAAL was 7.94 mg/L, while the median intake of vitamin C was 136.84 mg/d. There was a positive correlation between PAAL and intake of vitamin C (r=0.41; p<0.001). The values of PAAL and intake of vitamin C calculated by FFQ were divided into quartiles, and the rate of the classifying into the same or adjacent quartile was 81.4%. Conclusion: In conclusion, this questionnaire can be used to determine intake of vitamin C in Turkish adults.