Shaik et al., 2019 - Comments

All adverse health effects of fluoride are related to thyroid hormone metabolism.
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Shaik et al., 2019 - Comments

Post by wendy »

  • Shaik N, Shanbhog R, Nandlal B, Tippeswamy HM - "Fluoride ingestion and thyroid function in children resident of naturally fluoridated areas - An observational study" J Clin Exp Dent 11(10):e883-e889 (2019) doi: 10.4317/jced.55812. PMID: 31636857; PMCID: PMC6797461
  • NOTE: This work was published in two different journals - the second publication is:

    Shaik N, Shanbhog R, Nandlal B, Tippeswamy HM - "Fluoride and Thyroid Function in Children Resident of Naturally Fluoridated Areas Consuming Different Levels of Fluoride in Drinking Water: An Observational Study"
    Contemp Clin Dent 10(1):24-30 (2019) doi: 10.4103/ccd.ccd_108_18
The study was conducted by 4 dentists in Karnataka, India. Throughout the paper it becomes evident that the agenda is to show that "naturally" fluoridated areas at levels comparable to "optimal" concentrations do not cause thyroid dysfunction. Vital studies are not cited, instead pro-fluoridation organizations such as the British Fluoridation Society are cited as authorities.

There are many things wrong with this study, from determination of F- in water/serum levels, to the gender make-up of study groups. No indication is given if free or total thyroid hormones were measured. From the figures, it appears that total fractions were measured, not FT3 and FT4. Serum fluoride levels indicate that there are other sources of fluoride. It is therefore not surprising that children in the area with the lowest fluoride water concentration already have increased mean TSH levels compared to other recent investigations, and that the occurrence of dental fluorosis rises with an increase in T3 levels. 88 % of children have dental fluorosis in the area with 1.44 ppm fluoride in the water.

However, in spite of all the flaws in this study, the author's ignorance of thyroid hormone metabolism is what ultimately proves the study's downfall.

Shaik et al. claim that fluoride in water at the levels used in this study (0.02 -1.4 ppm) does not cause any changes in thyroid hormones. Based on the data presented this conclusion is incorrect.

An increase in the T3/T4 ratio is clearly seen between the no/low fluoride area (Group 1) compared to the two higher ones.
  • T3/T4 Ratio:
    Group 1: 14.69
    Group 2: 17.84
    Group 3: 17.04
This data is consistent with other evidence from fluoridated waters in areas where iodine intake is sufficient or excessive. An increase in the T3/T4 ratio is normally seen as a sign of mild thyroid insufficiency, representing an autoregulatory adaptive response of the thyroid, augmenting the relative synthesis and release of T3 over T4 (Pedraza et al., 2006).

Table: ... k_2019.png

Pedraza PE, Obregon MJ, Escobar-Morreale HF, del Rey FE, de Escobar GM - "Mechanisms of adaptation to iodine deficiency in rats: thyroid status is tissue specific. Its relevance for man" Endocrinology 147(5):2098-108 (2006)
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Re: 2019 Shaik et al - Comments

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The authors are obviously not familiar with the finer aspects of thyroid hormone metabolism.

It is very shoddy work. The F- in water concentrations are conflicting throughout the paper.

First they are described as:

"Drinking water fluoride level in group I, II and III fell in the range of 0.12 to 0.32 (mean of 0.22.), 0.76 to 1.1 (mean of 0.83) and 1.43-1.46 (mean of 1.44) respectively."

However, the table lists 0.01 to 0.6 in group I (mean 0.22), 0.7 to 1.2 in II (mean 0.89), and 1.3 to 2 (mean 1.44) in III.

A little later III is described as having F- at 1.3 to 1.8, a third variation!

What were the real levels?

The gender make-up is described as:

I boys 42% Girls 59%
II boys 41% Girls 61%
III Boys 60 % girls 37%

As you can see, composition of group III is opposite to that of I and II. This alone can manipulate the data.

Ponikvar M - "Chapter 12 - Exposure of Humans to Fluorine and Its Assessment" Fluorine and Health, Molecular Imaging, Biomedical Materials and Pharmaceuticals, Pages 487-549 (2008) ... 0868000126

Taves DR - "Normal human serum fluoride concentrations" Nature 211(5045):192-3 (1966)
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