Validation and reproducibility of an iodine and selenium specific food frequency questionnaire in breastfeeding women : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Albany, New Zealand
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Date
2023
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Massey University
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Abstract
Backgrounds: New Zealand has poor levels of iodine and selenium in its food sources. During lactation, women have increased selenium and iodine requirements, as their breastfeeding infant relies on their intake, putting them at increased risk of deficiency. Thyroid function is impacted by iodine and selenium status, and if these nutrients are low can cause consequences for the mother and breastfed infant. Dietary assessment methods, such as a Food Frequency Questionnaire (FFQ), can be utilised to assess nutrient intake, and validating an FFQ shows that the questionnaire can be used on the intended population to predict nutrient intake. To the best of our knowledge, New Zealand currently does not have a valid iodine and selenium specific FFQ for breastfeeding women. Due to this population risk with iodine and selenium, it is justified to test the validity and reproducibility of this FFQ on breastfeeding women in New Zealand. Aim: The aim of this study is to assess the validity and reproducibility of an iodine and selenium specific Food Frequency Questionnaire for breastfeeding women living in New Zealand. Methods: As part of the Mother and Infant Nutrition Investigation study (MINI), data was collected from breastfeeding mothers from three months to 12 months postpartum (PP). Participants (n = 87) were administered an iodine and selenium specific FFQ at three months and a four-day diet diary (4DDD). To assess reproducibility the FFQ was readministered at 12 months PP (FFQ2). FFQ1 was validated via 4DDD and selected biomarkers (urinary and breastmilk iodine concentrations and plasma selenium); statistical analysis was used, including Wilcoxon signed ranked test, Spearman’s correlation, cross-classifications, weighted kappa statistics, Bland Altman plots, the same statistical analysis carried out to assess reproducibility between FFQ1 and FFQ2. Results: For the validation, the correlation observed ranged from 0.317 (selenium) to 0.532 (total iodine) between the FFQ and 4DDD and for FFQ to EIB, 0.146 (selenium) and 0.155 (total iodine). Cross-classifications majority of the nutrient groups were >50% correctly classified (32.9% (selenium) to 71.6% (iodine food only)) when comparing the FFQ to 4DDD. Most of the groups were <10% misclassified (1.37% (iodine and salt) to 11.0% (selenium)). For the FFQ to EIB, the correctly classified participants were 50% (iodine) and 73.1% (selenium), and the grossly misclassified participants were 16.35% (iodine) and 3.4% (selenium). For FFQ to 4DDD, the weighted kappa values showed poor agreement (k<0.21) for two groups and fair agreement (k 0.21-0.41) for three groups. For EIB, the weighted kappa showed poor agreement (k<0.21) for four groups and fair agreement (k 0.21-0.41) for one. The Bland-Altman plots showed fair agreement for the difference between FFQ1 to 4DDD or EIB. For reproducibility, the correlation between FFQ1 and FFQ2 was 0.625 (iodine) and 0.429 (selenium). Cross-classification for correctly classified participants was >50% for iodine; for selenium and iodine, <10% were grossly misclassified. The weight kappa value showed poor agreement (k0.21) for both iodine and selenium. Conclusion: The FFQ showed reasonable validity when assessing iodine and selenium intake using the FFQ for breastfeeding women in New Zealand and showed good reproducibility for iodine and selenium. This FFQ could be used in future research on this population and could be used in primary care as a convenient way to assess iodine and selenium intake for breastfeeding women in New Zealand.
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Keywords
iodine, selenium, FFQ, breastfeeding, lactation, validation, reproducibility, dietary assessment, questionnaire