May 2007: Validation of Three Food Frequency Questionnaires to Assess Dietary Calcium Intake in Adults

Summary

The objective of this study was to assess the accuracy of three self-administered food frequency questionnaires (FFQs) to measure dietary calcium intake in healthy adults. Estimates of dietary calcium intake from two recently developed and one previously validated FFQ were compared with those from 7-day food records.
The previously validated FFQ was a 36- page Dietary History Questionnaire (DHQ) developed by the National Cancer Institute to assess total diet. It includes 124 separate food items and respondents are asked to select a frequency category indicating how often each food item was consumed over the past 12 months, as well as choose the portion size from three ranges. DHQs were analyzed using Diet*Calc Analysis Program.
A 3-page Calcium Questionnaire was also used. It is an 87-item FFQ developed by clinical research registered dietitians (RDs). In this FFQ, subjects are asked to write in the number of times each food is eaten by day, week, or month during the past year. Subjects are asked to indicate whether their portion was small, medium, or large, based on a reference medium portions size listed for each item. Two pages of food model and utensil drawings are provided to help subjects determine portion-size. To determine calcium intake, dietary calcium contents were entered into a spreadsheet.
The Short Calcium Questionnaire used in this study was designed by one of the authors to assess usual calcium intake rapidly. It is a 1-page, 25-item FFQ developed from the Calcium Questionnaire, reflecting major dietary sources of calcium. Subjects are asked to write in the number of servings eaten in a typical week for each food item listed (a reference serving size is included). Foods are grouped by calcium content per serving. These questionnaires were hand-calculated.
While all three FFQs allowed the opportunity for subjects to estimate calcium intake form calcium supplements, calcium-containing multivitamin/mineral supplements, and antacids, this data was not included in the study because supplement intake was not recorded on food records. Therefore the analyses in this study reflect only dietary calcium intake.
Results showed that all three FFQs performed well, but not perfectly to estimate dietary calcium intake obtained form 7-day food records. Mean calcium intakes from food records and all three FFQs were similar to mean calcium intake from food reported for a national sample (NHANES 2001-2002), based on two 24-hour recalls. Although relatively small, the DHQ showed the greatest underestimation of calcium intake. The DHQ may be a good choice when the intake of several nutrients is being assessed. The Calcium Questionnaire would appear to be a good tool for assessing usual calcium intake in a research setting where relative intake is of interest. The Short Calcium Questionnaire would be best used as a simple tool for quickly estimating calcium intake for treatment decisions or for screening purposes.