Development of a Semi-quantitative Food Frequency Questionnaire for Dietary Studies - Focus on Vitamin C Intake

The present work aimed to provide a basis for examination of intake of selected food items determined witha semi-quantitative food frequency questionnaire (SQFFQ) and planned-food selection (PFS). From Februaryto July of 2003, ninety one cancer patients and 90 matched (sex and age ± 5 years) non-cancer patients weredirectly interviewed by trained interviewers using the designed questionnaire at the inpatient-department ofViet Duc hospital, Ha Noi City, Viet Nam. Study subjects consumed more SQFFQ-food items than PFS-fooditems, so that the latter method might not accurately reflect dietary habits regarding estimation of nutrientintake, especially vitamins. Because these are beneficial factors acting against cancer development at manysites, the absence of food items selected by SQFFQ may result in a poor database regarding possible confoundingfactors. For futher clarification we then focused on vitamin C contributions of Vietnamese food and analyzeddata of the National Nutritional Household Survey in 2000: 7,686 households throughout the country (vitaminC intake status) and 158 households with 741 persons of the population of Hanoi city (individual food itemscontributing to vitamin C). Direct interview using a validated questionnaire with an album of current Vietnamesefood items-recipes and weighing checks was conducted to obtain information regarding all types of food intakeover the last 24-hours. Contribution analysis using the Nutritive Composition Table of Vietnamese Foods, revision2000, and stepwise regression analysis was applied. Average intake adjusted by ages of vitamin C per person perday was estimated. In total, the study subjects were found to currently consume 184 food items. Average intakeof vitamin C was 72.5 mg per person per day at the national level: 57.9% from leafy vegetables, 33.4% fromfresh fruits, and 6.4% from non-leafy vegetables. For vitamin C contribution, the highest 25 food items contributedto a cumulative 95.3% of vitamin C intake with a cumulative R2=0.99.