Validation of a food frequency questionnaire for nutritional calcium intake assessment in Italian women

OBJECTIVE: To evaluate a food frequency questionnaire assessing calcium intake in women. DESIGN: : Estimates of calcium intake from the food frequency questionnaire were compared with those from 14 day records from 206 Caucasian women aged 25-75 y in Siena, Italy. SUBJECTS: Subjects were randomly recruited from the residents list of the city of Siena, Italy. Of the 250 initially recruited, 39 did not meet the inclusion criteria or failed to complete the diet record and five outliers were excluded before the statistical analysis on the basis that their diet record was unlikely to represent habitual intake. RESULTS: Mean dietary calcium intakes were 829+/-255 (s.d.) mg/day from the questionnaire and 818+/-260 (s.d.) mg/day from the diet record. The mean difference in intake by the two methods (-11.3+/-116.4 mg/day) did not differ significantly from zero. Specificity in classifying women consuming less than 800 mg/day calcium was 86.6%, and sensibility in classifying women consuming more than 800 mg/day calcium was 89.4%. CONCLUSIONS: The food frequency questionnaire could be used in epidemiological studies to assess calcium intake in young to elderly women. The specificity in identifying low calcium intake subjects makes it useful also as an educational tool in diet counselling and for prescribing calcium supplementation.