Validation of a short food frequency questionnaire for assessment of dietary calcium intake in women

Objective: To assess the ability of a short food frequency questionnaire to measure dietary calcium intake in women. Design: Estimates of calcium intake from the food frequency questionnaire were compared with those from seven-day estimated records in 58 Caucasian women aged 25-49 years in Dunedin, New Zealand. Subjects: Subjects were recruited through poster and newspaper advertising around the central business district of Dunedin, New Zealand. Of 69 subjects initially recruited, nine failed to complete diet records and two were excluded on the basis that their diet record was unlikely to represent habitual intake. Results: Mean dietary calcium intakes were 808.1 mg/day from the estimated record and 776.9 mg/day from the questionnaire. The mean difference in intake by the two methods (31.1 mg, SD = 234.0, 95% CI = -30.4-92.7, p = 0.3) did not differ significantly from zero. The questionnaire classified women consuming less than 800 mg calcium per day with 78% specificity. 81% of subjects when classified by the records fell into the same or adjacent quartiles when classified by the questionnaire. Only two subjects were grossly misclassified. Conclusions: The short food frequency questionnaire could be used to assess mean dietary calcium intake in young to middle aged women. The specificity of the questionnaire is high in identifying women who consume <800mg calcium/day, therefore it could be used to target interventions for those with intakes below this level.