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Fluoride exposure and indicators of thyroid functioning in the Canadian population: implications for community water fluoridation
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  • Published on:
    Response to Barberio et al's claim that there is no link between fluoridation and hypothyroidism
    • Stephen Peckham, Professor of Health policy Centre for Health Services Studies, University of Kent
    • Other Contributors:
      • David Lowery, Research Fellow
      • Sarah Spencer, Research associate

    Barberio et al1 report a study which – in contrast to our own study2 - shows no relationship between fluoride intake and hypothyroidism. However, Barberio et al study is limited by the methods used for identifying hypothyroidism prevalence, fluoridation status and sample sizes.

    Barberio et al utilised three methods to determine hypothyroidism prevalence: self-report and two biomarkers: thyroid-stimulating hormone (TSH), and free T4 blood results. This is problematic as self-report is unlikely to provide accurate prevalence data when compared to clinical diagnosis data, as used in our study4; and there are a number of studies demonstrating that self-reported estimates of thyroid functioning are unreliable. Further, the self-report question does not appear to differentiate between under and over active thyroid functioning. The biomarker data only included individuals with un-medicated hypothyroidism; consequently, the sample is unrepresentative of the population. The analysis of this data provides correlations between the biomarkers TSH, T4 readings and fluoride exposure in a sub-sample of respondents, assuming that all respondents received uniform levels of fluoride. From our data, we observed wide variability within fluoridated areas. This may explain why in table 2b, none of the variables, including age and sex, were predictive of TSH levels. This contradicts Barberio et al’s own data on what is predictive of hypothyroidism and the Canadian Health Measures Survey...

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    Conflict of Interest:
    None declared.