Fluoride exposure and indicators of thyroid functioning: study design and data analysis considerations

Barberio et al1 reported that there was no evidence of a relationship between fluoride exposure and the diagnosis of a thyroid condition among a subsample of respondents available from Statistics Canada's Canadian Health Measures Survey. On review, however, their data show that the mean urinary fluoride (UF) level in patients with primary hypothyroidism was 0.60 mg/L compared with 0.55 mg/L for individuals without this condition. In other words, the mean UF levels in respondents with primary hypothyroidism were higher than without. However, it is the reported ranges of UF levels from either groups that is particularly revealing. For example, among individuals with primary hypothyroidism, UF levels were found to range from 0.22 to 0.98 mg/L. The range reported in the controls was 0.49 to 0.61 mg/L.1 What these data show is that among patients with primary hypothyroidism, a subgroup of patients had very low UF levels with another subgroup...

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