Fluoride and the thyroid

Does a healthy teeth treatment make our thyroid weaker?


Excess of fluoride has toxic effects on many tissues: teeth, bones and the thyroid gland. Thyroid problems caused by excessive fluoride intake are very similar to those caused by iodine deficiency. Research-wise, this is still a controversial topic with scientific publications reporting conflicting results.

What is Fluoride?

Fluoride is the 13th most abundant chemical element in the world, it is present in the air, water, soil and rocks. It is used in production of pesticides, ceramics, glassware, Teflon, and more (1).

Fluoride as a preventive solution for dental caries began in 1945 by water fluoridation. This has become a standard procedure since then in many places around the world.

Recently, research and opinions of scientific leaders have emerged both having for and against fluoridation. It is still unclear how good the fluoride is in preventing the caries, with some studies reporting almost no benefit at all (2). In addition, it is not confirmed to which extent it impacts the thyroid, but the evidence is increasing. One of the big problems in doing research on fluoride is that there is no way in controlling for the dosage.

Which countries have fluoridated water?

There are at least 30 countries that do or did have fluoridated water in the past. Germany, The Netherlands, Sweden and Switzerland stopped fluoridating water because of concerns about both effectiveness of fluoridation against caries and safety of use (3, 4).

Australia, Malaysia, New Zealand, Singapore and The USA fluoridate more than 50% of the water supply. Research estimates today there is about 5% of the world’s population that consume fluoridated water (5).

What happens when a lot of Fluoride is ingested?

If a person ingests large quantities for a prolonged period of time, it will lead to a state called fluorosis. This most commonly happen by drinking water, and with tooth paste. This is a big problem in China, India and Mexico (6).

The thyroid gland is one of the most fluoride-sensitive tissues in the body

Fluoride interferes with the function of the thyroid gland, and is causing problems with the brain development and function (7, 8). But not all the people that are exposed to the same amount of fluoride in drinking water end up with fluorosis or thyroid problems, as factors like environment (climate, duration and the amount of drinking, addition of other salts in the water etc) and individual predisposition (genetics, individual biology) greatly affect the likelihood of developing any type of health complications (9).

Fluoride increases the concentration of TSH (thyroid-stimulating hormone), and decreases T3 and T4, which is a classical feature of hypothyroidism. In cases of prolonged fluoride exposure the entire function of the thyroid gland will be suppressed and TSH levels will go down (10).

How can fluoride have such an impact on thyroid?

To answer this question, we have to dig a bit into chemistry. Fluoride can disrupt thyroid gland function in several ways:

  1. Fluoride can mimic thyroid stimulating hormone (TSH), it can enhance TSH effects and modify T4 to T3 conversion (11,12).

  2. Fluoride interferes with deiodinases, enzymes necessary to convert T4 into T3 (13).

  3. Fluoride interferes with iodide transport. It is more electronegative than iodine, and it easily forces iodide out of the thyroid gland (13).

  4. Fluoride disturbs the balance between reverse T3 (rT3) and T3 (13).

Fluoride activity on the thyroid especially affects areas with low iodine (11, 12).

Up until forty years ago fluoride was prescribed as a treatment of overactive thyroid gland caused hyperthyroidism.

What are your experiences with fluoride? We would love to know more.


  1. United States Environmental Protection Agency. Report to Congress. section 112 (n) (16) Washington, DC, USA: Clean Air Act; 2000. Fluoride.

  2. Warren JJ, et al. Considerations on optimal fluoride intake using dental fluorosis and dental caries outcomes — a longitudinal study, 2009

  3. Pizzo G, et al. Community water fluoridation and caries prevention: a critical review, 2007

  4. National Health. Public Statement: The Efficacy of Fluoridation, 2007

  5. Peckham S, et al. Water Fluoridation: A Critical Review of the Physiological Effects of Ingested Fluoride as a Public Health Intervention, 2014.

  6. Mahadevi BH, et al. Study of thyroid hormones free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) in subjects with dental fluorosis, 2012.

  7. Susheela AK, et al. Excess fluoride ingestion and thyroid hormone derangements in children living in Delhi, India, 2005

  8. National Research Council (NRC) Fluoride in Drinking Water: A Scientific Review of EPA’s Standards. Washington, DC, USA: National Academies Press, 2006.

  9. Choubisa SL. Endemic fluorosis in southern Rajasthan, India, 2001.

  10. Ge Y, et al. DNA damage in thyroid gland cells of rats exposed to long term intake of high fluoride and low iodine, 2005

  11. Idris EA, et al. Adverse effects of fluoride towards thyroid hormone metabolism, 2008

  12. Zhan XA, et al. Effects of fluoride on growth and thyroid function in young pigs, 2006

  13. Clinch C. Fluoride interactions with iodine and iodide: implications for breast health, 2009

  14. Hetzel BS, et al. The iodine deficiency disorders: nature, pathogenesis and epidemiology, 1990

  15. Martins CC, et al. Effect of discontinuation of fluoride intake from water and toothpaste on urinary excretion in young children, 2011

  16. VVilla A, et al. Relationships between fluoride intake, urinary fluoride excretion and fluoride retention in children and adults: an analysis of available data, 2010

  17. Visser JT, et al. Clinical summary In Metabolism of Thyroid hormone. Endocrine Education, Massachusetts.