Questionnaire about calcium intake: can we trust the answers?

The aim of this study was to construct and evaluate reliable questions concerning calcium intake and to include them in a questionnaire to be used in a community-based intervention program for preventing osteoporosis. Estimating calcium intake is an important factor in evaluating risk profiles for community residents. A very large amount of calcium in the Swedish diet comes from dairy foods. Two questionnaires were designed. Questionnaire A contained eight questions concerning consumption of dairy foods. Questionnaire B contained 52 questions on consumption of calcium-rich food groups and dishes, and also included the eight questions mentioned above. Questionnaire A was sent to 467 randomized women aged 20-30 and 50-60 years. Women with a low calcium intake also answered questionnaire B. In order to validate the questionnaires a selected number of the women were interviewed using a dietary history. In total 363 women answered questionnaire A, 118 of whom had a calcium intake below the recommended amount. Ninety-six women completed questionnaire B. Twenty-two women were interviewed with the dietary history. Statistical analyses using t-tests of the differences between answers to the same questions in two questionnaires and the interview, gave the following results. Questionnaire A provides reliable information about those who do not reach the recommended level of calcium intake. Questionnaire B does not provide any more information than questionnaire A. It is not possible to rank calcium levels in the diet with the questionnaires. Using the estimated calcium intake from dairy foods obtained in questionnaire A, individuals at risk of consuming less than the recommended intake of calcium can be identified, as can those consuming the required amount. In conclusion, questionnaire A is useful in discriminating between subjects with low and high calcium intake.