Validation of a quantitative food frequency questionnaire for rapid assessment of dietary calcium intake

This study tested the accuracy of a quantitative food frequency questionnaire (FFQ) designed to assess the amount of calcium consumed daily and to use as an educational tool in diet counseling and for prescribing calcium supplementation. The subjects were 26 perimenopausal women, aged 48 to 56 years, who were participants in a longitudinal osteoporosis study. Diets of the subjects were studied during the winter and summer of one year. Subjects filled out a food frequency questionnaire and the next week completed 4-day food intake records according to instructions from the researchers. The mean daily intake of calcium estimated from the food frequency questionnaire was 928 mg in the winter and 912 mg 6 months later. Ranges in the winter were 227 to 2,243 mg calcium and in the summer 198 to 3,063 mg calcium. The 53-item FFQ included descriptions of portion sizes and a calcium index for each item and had options for two frequency periods. The calcium level estimated from the questionnaire correlated (r = .73 in winter and r = .84 in summer) with the estimated amount from 4-day records. A seasonal difference was not found. The brief time (less than 5 minutes by a dietitian) required to calculate the amount of calcium consumed daily from the food frequency questionnaire could make it an important clinical tool.