skip to main content



Fluoride and the thyroid

POSTED: 1 August 2018

The Thyroid

The endocrine system is made up of glands that produce and secrete hormones which are chemical substances produced in the body that regulate the activity of cells or organs. These hormones regulate the body's growth, the physical and chemical processes of the body and sexual development and function.

The thyroid gland, or simply the thyroid, is an endocrine gland in the neck. It is found at the front of the neck, below the Adam's apple. The thyroid gland secretes thyroid hormones which primarily influence metabolic rate and protein synthesis. The hormones also have many other effects including being important for development.

Endocrine-disrupting chemicals

In The Lancet, Volume 6, March 2018, is a review of a 2017 publication, Toxic Cocktail: How Chemical Pollution is Poisoning our Brains, by Barbara Demeneix who is an internationally recognised expert on thyroid function and endocrine disruption. Toxic Cocktail is published by Oxford University Press.

In this and others of her published works Demeneix makes the case that environmental chemicals that disrupt normal thyroid function pose significant risks to the inherited intelligence and mental health of future generations.

In Toxic Cocktail, Barbara Demeneix asks how the thousands of industrial chemicals synthesised over past decades collectively affect our brains and those of future generations.

She is particularly concerned about those chemicals that disrupt the thyroid as thyroid hormones have a crucial role in brain development, beginning in the fetus and continuing through childhood. These early life stages are the very ones during which endocrine-disrupting chemicals have the greatest impact with long-term and potentially irreversible effects.

Demeneix declares that thyroid disruptors are diminishing brain capacity and creating a human brain drain and that population studies show that there is an inverse relation between intelligent quotient (IQ) and higher prenatal exposures to industrial chemicals. She also declares that robust regulatory mechanisms must be in place to ensure safety, especially for chemicals that are swallowed by people, like medical treatments and food additives, or distributed into the environment.

Is fluoride an endocrine-disrupting chemical?

In providing background to a discussion on fluoride and the thyroid the major study, National Research Council. 2006. Fluoride in Drinking Water: A Scientific Review of EPA's Standards, Washington, DC, The National Academies Press, said that an effect of fluoride exposure on the thyroid was first cited in various reports approximately 150 years previously and in 1923, the director of the Idaho Public Health Service reported enlarged thyroids in many children between the ages of 12 and 15 using city water in Oakley.

That city’s children also had severe dental fluorosis in permanent teeth which was eventually attributed to the presence in the city water of 6 mg/L fluoride. Children born after a change to water supply with less than 0.5 mg/L fluoride were not so affected.

An early and reliable example of endocrine disruption by fluoride occurred in New York State when a wide health effects comparison was made between fluoridated Newburgh and non-fluoridated Kingston, a city of similar size and population mix.

Schlesinger and colleagues, in Newburgh-Kingston caries-fluorine study XIII. Pediatric findings after ten years found that the mean age of menstruation for girls in fluoridated test city Newburgh was 5 months earlier than the non-fluoridated control city, Kingston.

The authors of the National Research Council report stated, “Several lines of information indicate an effect of fluoride exposure on thyroid function.” They recommended that:

  • Further effort is necessary to characterize the direct and indirect

           mechanisms of fluoride’s action on the endocrine system and the factors

           that determine the response, if any, in a given individual and that;

  • better characterization of exposure to fluoride is needed in population-wide studies investigating potential endocrine effects of fluoride.

The Endocrine Society

The United States Endocrine Society has published a major report titled Introduction to endocrine disrupting chemicals – A guide for public interest organisations and policy-makers (Andrea C. Gore, PhD, et al. 2014).

An endocrine-disrupting chemical is defined by the Endocrine Society as a non-natural chemical, or mixture of chemicals, that interferes with any aspect of hormone action. The society also reports that endocrine-disrupting chemicals can have effects at extremely low doses (even at the part-per-trillion to part-per-billion range) to regulate bodily functions and that this concept is particularly important in considering that exposures start in the womb and continue throughout the life cycle.

It is for that reason that a new type of testing is needed in order to reflect that endocrine-disrupting chemicals impact human health even at the low levels encountered in everyday life – like fluoride in community water supplies.

The view on this issue by the New Zealand Ministry of Health

When asked through an April, 2018, request under the Official Information Act what advice had the Ministry of Health provided directly or instructed district health boards or fluoridated water system operators to provide to the general public on the effect that fluoride has on endocrine systems and thyroid functions the bland response was:

 “Refused under 18(e) [of the Act] - this information does not exist - The Ministry does not hold the information requested.”

The Ministry was also provided with the definition of the Precautionary Principle which states that if an action or policy has a suspected risk of causing harm to the public domain (affecting general health or the environment globally), the action should not be taken in the absence of scientific near-certainty about its safety and that under these conditions, the burden of proof about absence of harm falls on those proposing an action, not those opposing it.

It also stated that the Precautionary Principle is intended to deal with uncertainty and risk in     cases where the absence of evidence and the incompleteness of scientific knowledge carries potentially serious implications for society. (See: Taleb et al., The Precautionary Principle: Fragility and Black Swans from Policy Actions, University of East Anglia, 2014)

An associated request for information was that:

  • Considering that the definition above clearly states that the burden of proof about absence of harm falls on those proposing an action (say nation-wide fluoridation), not those opposing it, will the Ministry of Health please provide fully detailed documentation of any internal Ministry of Health consideration of a precautionary policy in relation to an apparent intention to proceed with the Health (Fluoridation of Drinking Water) Amendment Bill?

  • If the Ministry of Health has had such consideration and subsequently determined that nation-wide fluoridation is a firm policy option please provide Level A evidence, that there is scientific near-certainty about the safety of community fluoridated water to all consumers.

Again, the bland Ministry response was: “Refused under 18(e) - this information does not exist - The Ministry does not hold the information requested.”


    Join The Campaign

Help us with donations:
 Please make a donation to help our hundreds of volunteers to pay for campaign messages.

Tell your MP: Tell him or her that you support Rethink Fluoride. Talk to them in person or find their contact details here to send them a message.

Post a blog: That's right. We make it easy for you to contribute your views. Please be reasonable and patient while we approve each post.

+ Text Size -
Original generation time 1.7532 seconds. Cache Loaded in: 0.0350 seconds.