Wasserglas wird am Wasserhahn gefüllt

Switch to other approaches in bid to protect tooth health, say researchers

  • Study raises particular concerns about the validity of community fluoridation as a safe public health measure
  • Higher levels of fluoride in drinking water provide a useful contribution for predicting prevalence of hypothyroidism. 
  • Water fluoridation above a certain level is linked to 30 per cent higher than expected rates of underactive thyroid (hypothyroidism) in England
  • GP practices located in the West Midlands (a wholly fluoridated area) are nearly twice as likely to report high hypothyroidism prevalence in comparison to Greater Manchester (non-fluoridated area)

Fluoride and Thyroid function

thyroidpicThe relationship between fluoride and the thyroid is long. In the 1950s, fluoride was used as a treatment for hyperthyroidism. It was chosen as a thyroid suppressant based on links that had been noticed between fluoride and goitre, and fluoride therapy did reduce thyroid activity in the treated patients.

The dose effective for treatment was typically between 2 and 5 mg fluoride per day and this dose is within the range commonly consumed by individuals living in fluoridated areas.

The researchers of this study, published online in the Journal of Epidemiology & Community Health, also point out that two reviews have examined the impact of fluoride on thyroid function “concluding that fluoride is an endocrine disruptor with the potential to disrupt the function of tissues that require iodine. In particular, it was suggested that the chief endocrine effect is decreased thyroid function at fluoride exposure levels as low as 0.01 mg/kg/day where iodine intake is inadequate.”

 Water fluoridation in England

In England, around 10 per cent of the population (6 million) live in areas with a naturally or artificially fluoridated water supply of 1 mg fluoride per litre of drinking water. This makes it a good location for comparison as there are large populations exposed and not exposed to fluoridation.

The researchers looked at the 2012 levels of fluoride in the drinking water supply, using data provided by the Drinking Water Inspectorate for individual postcodes.

And they looked at the national prevalence of underactive thyroid diagnosed by family doctors in England in 2012-13. Complete data were provided for 7935 general practices out of a total of 8020.

The researchers also carried out a secondary analysis, comparing two built up areas, one of which (West Midlands) was supplied with fluoridated drinking water, and the other of which (Greater Manchester) was not.

After taking account of influential factors, such as female sex and older age, both of which are linked to increased risk of hypothyroidism, they found an association between rates of the condition and levels of fluoride in the drinking water.

In areas with fluoride levels above 0.7 mg/l, they found higher than expected rates of hypothyroidism than in areas with levels below this dilution.

High rates of hypothyroidism were at least 30% more likely in practices located in areas with fluoride levels in excess of 0.3 mg/l. And practices in the West Midlands were nearly twice as likely to report high rates of hypothyroidism as those in Greater Manchester.

This is an observational study so no definitive conclusions can be drawn about cause and effect, and the researchers emphasise that they were not able to take account of other sources of fluoride found in dental products and food and drink.

But they point out that their findings echo those of previous research, and that while they were only able to look at diagnosed hypothyroidism, there might also be other cases of impaired thyroid function that have not yet been diagnosed—and treated.

The findings prompt the researchers to call for a rethink of public health policy to fluoridate the water supply in a bid to protect the nation’s tooth health.

“Consideration needs to be given to reducing fluoride exposure, and public dental health interventions should stop [those] reliant on ingested fluoride and switch to topical fluoride-based and non-fluoride-based interventions,” they conclude.

open denture with toothpaste tube and toothbrush
Regular brushing with fluoride-based toothpaste should be adequate for dental health.

Campaigns against Fluoridation – the case in Ireland

  • Ireland water fluoridation rate is 71% – the rate of congenital hypothyroidism in Ireland is the highest in the EU

According to a report prepared by EnviroManagement Services, Ireland on Water Fluoridation and Fluoride Exposure “no accurate data is available on prevalence of thyroid disorders in Ireland however it is estimated that there are in the region of over 300,000 people in the Republic of Ireland with a thyroid disorder representing approximately 7% of the population.”

As areas with reduced iodine intake are even more susceptible to negative effects from fluoride it is also troubling to note that “according to the WHO the population of the Republic of Ireland are deficient in iodine intake. The WHO report also noted that a high degree of apathy has been noted in populations living in severely iodine deficient areas.”

The report also states that:

“Subclinical hypothyroidism (SCH), affects about one in six people over the age of 65 in Ireland.

Subclinical hypothyroidism is associated with increased cholesterol concentrations increased incidence of depression, diminished response to standard psychiatric treatment, cognitive dysfunction, and, in pregnant women, decreased IQ of their offspring.”


In Ireland since the early 1970’s there has been a documented 2.5 fold increase in thyroid cancers. This period happens to also coincide with water fluoridation in Ireland. It is interesting to observe that thyroid cancer rates in Sweden reduced by 18 per cent in the period after cessation of water fluoridation.

The report questions “the safety of a public health policy that mandates the addition of fluoride chemicals to drinking water that is itself deficient in iodine, to be consumed by a population that already have insufficient iodine intake” as with this combination of circumstances “it is to be expected that certain health impacts may arise in the population.”


A campaign in Ireland called Fluoride Free towns is gathering support. Bantry, a seaside town in scenic West Cork in Southern Ireland, was the first to declare fluoride free status when businesses installed water filtration systems that give customers the choice to consume food and drinks prepared with fluoride-free water. Many towns are now following suit.

While many still argue for the benefits of fluoridation on dental health, the UK study in particular is significant and raises important public health questions concerning fluoridation policies. The call for a rethink on fluoridation policy should certainly be given serious consideration.

Sources/More information:

UK Study

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 Online First doi 10.1136/jech-2014-204971 http://jech.bmj.com/lookup/doi/10.1136/jech-2014-204971

The Journal of Epidemiology & Community Health is one of more than 50 specialist journals published by BMJ. The title is the official journal of the Society of Social Medicine.  http://jech.bmj.com

Irish Report

Public Health Investigation of Epidemiological data on Disease and Mortality in Ireland related to Water Fluoridation and Fluoride Exposure  Key findings and observations on Fluoride by the U.S National Research Council examined within the context of a comparison of population health and disease burdens between Fluoridated Republic of Ireland and Non- Fluoridated Northern Ireland and Europe.

Report for The Government of Ireland, The European Commission and World Health Organisation Prepared By Declan Waugh BSc. CEnv. MCIWEM. MIEMA. MCIWM  March 2013  http://www.enviro.ie/Feb2013.pdf

About the thyroid gland