Development and Evaluation of Validity of Dish Frequency Questionnaire (DFQ) and Short DFQ Using Na Index for Estimation of Habitual Sodium Intake

Son, Sook Mee; Huh, Gwui Yeop; Lee, Hong Sup

Abstract

The assessment of sodium intake is complex because of the variety and nature of dietary sodium. This study intended to develop a dish frequency questionnaire (DFQ) for estimating the habitual sodium intake and a short DFQ for screening subjects with high or low sodium intake. For DFQ112, one hundred and twelve dish items were selected based on the information of sodium content of the one serving size and consumption frequency. Frequency of consumption was determined through nine categories ranging from more than 3 times a day to almost never to indicate how often the specified amount of each food item was consumed during the past 6 months. One hundred seventy one adults (male: 78, female: 93) who visited hypertension or health examination clinic participated in the validation study. DFQ55 was developed from DFQ112 by omitting the food items not frequently consumed, selecting the dish items that showed higher sodium content per one portion size and higher consumption frequency. To develop a short DFQs for classifying subjects with low or high sodium intakes, the weighed score according to the sodium content of one protion size was given to each dish item of DFQ25 or DFQ14 and multiplied with the consumption frequency score. A sum index of all the dish items was formed and called sodium index (Na index). For validation study the DFQ112, 2-day diet record and one 24-hour urine collection were analyzed to estimate sodium intakes. The sodium intakes estimated with DFQ112 and 24-h urine analysis showed 65% agreement to be classified into the same quartile and showed significant correlation (r = 0.563 p < 0.05). However, the actual amount of sodium intake estimated with DFQ112 (male: 6221.9 mg, female: 6127.6 mg) showed substantial difference with that of 24-h urine analysis (male: 4556.9 mg, female: 5107.4 mg). The sodium intake estimated with DFQ55 (male: 4848.5 mg, female: 4884.3 mg) showed small difference from that estimated with 24-h urine analysis, higher proportion to be classfied into the same quartile and higher correlation with the sodium intakes estimated with 24-h urine analysis and systolic blood pressure. It seems DFQ55 can be used as a tool for quantitative estimation of sodium intake. Na index25 or Na index14 showed 39~50% agreement to be classified into the same quartile, substantial correlations with the sodium intake estimated with DFQ55 and significant correlations with the sodium intake estimated with 24-h urine analysis. When point 119 for Na index25 was used as a criterion of low sodium intake, sensitivity, specificity and positive predictive value was 62.5%, 81.8% and 53.2%, respectively. When point 102 for Na index14 was used as a criterion of high sodium intake, sensitivity, specificity and positive predictive value were 73.8%, 84.0%, 62.0%, respectively. It seems the short DFQs using Na index14 or Na index25 are simple, easy and proper instruments to classify the low or high sodium intake group.