Excess fluoride ingestion and thyroid hormone derangements in children living in Delhi, India

Abstract

Ninety children with dental fluorosis, aged 7-18, living in fluoride endemic, non-iodine deficient areas of the National Capital Territory of Delhi, India, where iodized salt has been promoted for over a decade, were investigated, along with 21 children in two control groups without dental fluorosis living in nonendemic areas, to determine their levels of free T₄ (FT₄), free T₃ (FT₃), and thyroid stimulating hormone (TSH). The drinking water fluoride of the 90 children in the sample group ranged from 1.1 to 14.3 mg F^-/L (mean 4.37 mg F^-/L); their serum ranged from 0.02 to 0.41 mg F^-/L (mean 0.14 mg F^-/L); their urine ranged from 0.41 to 12.8 mg F^-/L (mean 3.96 mg F-/L). The drinking water fluoride of the control I group (n = 10) ranged from 0.14 to 0.81 mg F^-/L (mean 0.23 mg F^-/L) and that of the control II group (n = 11) ranged from 0.14 to 0.73 mg F^-/L (mean 0.41 mg F^-/L). In control I, only 3 children had serum fluoride below the normal upper limit of 0.02 mg F^-/L. The remaining 7 children, even though they were consuming "safe" water, had elevated serum fluoride. In control II, only one child had serum fluoride below the normal upper limit. The remaining 8 children who were tested also had elevated serum fluoride. In control I, only 3 children had urine fluoride samples in the normal range (0.09-0.10 mg F^-/L); in the remaining 7 children they were above normal. In control II, only one child had urinary and serum fluoride within the normal range. In the remaining 8 children who were tested it was high, suggesting they had excess F^- exposure from sources other than drinking water. The hormonal status of the 90 sample children indicated that 49 (54.4%) had welldefined hormonal derangements. In the remaining 41 children the findings were borderline. The hormonal deviations among the affected 49 children fall into the following five categories: (1) high TSH with normal FT₄ and FT₃ (46.9%); (2) normal TSH and FT₄ with low FT₃ (32.7%); (3) high TSH and FT3 with normal FT₄ (14.3%); (4) high TSH with normal FT₃ but low FT₄ (4.1%); and (5) high TSH with normal FT₄ but low FT₃ (2.0%). In control I and control II, similar hormonal deviations were detected in as many as 50% and 45.4% of the children, respectively. These findings indicate that children with or even without dental fluorosis from exposure to excess fluoride, either through drinking water or through other sources, may have thyroid hormone derangements that may not be clinically overt until late stages. Determining free T₃, free T₄, and TSH is therefore important for a proper diagnosis of potential health problems. Withdrawal from fluoride sources along with measures to correct the thyroid hormonal status may be necessary to promote better health in such children living in fluoride endemic areas.