Fluoride in water linked to hypothyroidism

Posted on Wed, 1 Jun 16

A large scale study linking fluoride in drinking water to hypothyroidism raises strong concerns about the safety of fluoridated water. 

Fluoride is sometimes added to public drinking water as a public health measure against dental decay. However, the efficacy and safety of fluoridated drinking water is controversial with evidence suggesting it has questionable benefits for dental health and could adversely affect cognitive development in children and contribute to the development of illnesses such as hypothyroidism [1].

In fact, the link between hypothyroidism and fluoride should not be that controversial because fluoride was used as a medical treatment to suppress overactive thyroid function successfully in the 1950s [2]. And more recent experiments also suggest flouride reduces thyroid function by reducing hormone production and damaging the thyroid gland [3].

In England about 10% of the population consume fluoridated water and the diagnosis of hypothyroidism has been recorded since 2004, making it possible to see if there are associations between living in an area where water is fluoridated and the development of thyroid disease.  

By comparing medical records in fluoridated areas vs. non-fluoridated a research group from the University of Kent were able to show that there was a significantly higher prevalence of hypothyroidism in areas with high fluoride levels (>07 mg/L) compared with those with fluoride levels of 0.7 mg/L and below [4]. High hypothyroidism prevalence was at least 30% more likely in practices located in areas with fluoride levels in excess of 0.3 mg/L.

“The clear association found in our analyses between fluoride levels in drinking water and variations in hypothyroidism prevalence appears to confirm findings in earlier studies that ingestion of fluoride affects thyroid function,” commented the investigators. “From a public health perspective, this raises questions about the safety of community fluoridation and consideration should be given to reducing all sources of fluoride in the environment.”

References: 

1. Peckham S, Awofeso N. Water fluoridation: a critical review of the physiological effects of ingested fluoride as a public health intervention. ScientificWorldJournal. 2014 Feb 26;2014:293019.
2. Galletti PM, Joyet G. Effect of fluorine on thyroidal iodine metabolism in hyperthyroidism. J Clin Endocrinol Metab. 1958 Oct;18(10):1102-10.
3. Jiang Y, Guo X, Sun Q, Shan Z, Teng W. Effects of Excess Fluoride and Iodide on Thyroid Function and Morphology. Biol Trace Elem Res. 2016 Apr;170(2):382-9.
4. Peckham S, Lowery D, Spencer S. Are fluoride levels in drinking water associated with hypothyroidism prevalence in England? A large observational study of GP practice data and fluoride levels in drinking water. J Epidemiol Community Health. 2015 Jul;69(7):619-24.