Relative validity of an FFQ for assessing dietary fluoride intakes of infants and young children living in Iowa.

When seeking to assess dietary intakes at the population level, investigators have to consider many factors before choosing the type of dietary assessment tool. Factors to be considered include how detailed, population-specific and expensive the tool will be for the purpose of the study(1). Although multiple 24 h recalls and diet diaries can provide valid assessments of an individual’s usual intake and a level of detail not possible with other approaches, they can be very time-consuming and expensive to administer, complete and analyse. The level of detail provided by these approaches may not be necessary or practical for studies with large sample sizes(2). When conducting epidemiological studies with large sample sizes, it is often important to use a dietary assessment tool that is not only valid but also easy to use for both the research participant and the researcher, and that also minimizes costs(3). The FFQ was created in an attempt to obtain a self-administered, inexpensive and rapid estimate of usual intake and is usually constructed to emphasize the recording of the intake of one or more nutrients of interest. Fluoride has long been recognized as an effective agent in preventing dental caries. Constant, low levels of fluoride in the mouth help to prevent caries by promoting remineralization and by helping to inhibit demineralization (4). This low concentration of fluoride in the oral cavity is obtained through direct contact with fluoride agents (i.e. ingesting foods and beverages with fluoride) and also through the secretion of fluoride from the salivary glands as a result of systemic intake(5). The major health concerns of high levels of fluoride intake are increased risk of developing dental and/or skeletal fluorosis(4). Marshall et al.(2) evaluated the relative validity of a semiquantitative beverage questionnaire in assessing beverage volumes as well as Ca and vitamin D intakes using 3 d diet diaries for reference measurements. The Spearman correlations for beverage intake were high for human milk (r=0·99 at 6 months), infant formula (r=0·84 at 6 months), cow’s milk (r=0·86 at 6 months and r=0·76 at 12 months) and juice/juice drinks (r=0·69 at 6 months and r=0·64 at 12 months). Correlations for Ca and vitamin D at 6 months were r=0·64 and 0·80, respectively, compared with r=0·67 and 0·60, respectively, at 12 months. The correlation for water intake was not quite as high at 6 months (r=0·54) but increased to r=0·70 at 12 months. These findings are important because most dietary fluoride comes from beverages and these results show high correlations for beverage intake estimates between questionnaires and diaries. Araujo et al.(6) analysed the relative validity of a semiquantitative FFQ (in addition to estimating the calibration factors) designed to estimate the usual food intake of adolescents. The study sample consisted of adolescents living in Rio de Janeiro, Brazil. The Pearson correlation coefficients were r=0·17 for Fe intake, r=0·33 for total fat intake, r=0·46 for the intake of carbohydrates and r=0·47 for Ca and fibre intakes. Hacker-Thompson et al.(7) analysed the validity of two Ca-intake questionnaires. The study sample consisted of community-dwelling women over 18 years of age. The Pearson correlation coefficient for each Ca-intake questionnaire was r=0·37 when compared with the 3 d mean Ca intake from a 3 d food record. In 1997, the Institute of Medicine (IOM) released its upper limit (the level below which there is unlikely to be any adverse health effects in healthy people) recommendations for dietary intake of fluoride(8). The IOM recommended these upper limits to be: 0·7 mg/d, 0·9 mg/d, 1·3 mg/d and 2·2 mg/d for children from birth to 6 months, 7–12 months, 1–3 years and 4–8 years of age, respectively, based on 0·1mg fluoride/kg body weight and average weights for children of those ages. The IOM also released Adequate Intakes (AI; used as guides for nutrient intakes for individuals and generally regarded as being compatible with health) for fluoride ingestion(8). The IOM AI values for fluoride are 0·01, 0·5, 0·7 and 1mg fluoride/d from birth to 6 months, 7–12 months, 1–3 years and 4–8 years of age, respectively. Previous research has attempted to determine the relative validity of FFQ in estimating nutrient as well as food and beverage intakes. To date, no study has determined the relative validity of an FFQ that estimates the intake of dietary fluoride. The purpose of the present research was to determine the relative validity of an FFQ developed as part of the Iowa Fluoride Study (IFS) in assessing fluoride intakes using 3 d food and beverage diaries for reference measurements.