Fluoride and the Thyroid: The Controversy

Fluoride and Fluoridated Water's Link to Thyroid Disease

Woman standing in the bathroom brushing her teeth
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Water fluoridation is defined as the addition of industrial-grade fluoride chemicals -- typically hydrofluorosilicic acid or and sodium silicofluoride -- to the water supply, with the goal of helping prevent tooth decay. It's estimated that 70% of the water supply in the United States is fluoridated. This contrasts with most developed nations, including all of Japan and most of Western Europe, which do not have fluoridation programs.

The fluoridation of local water supplies in the United States has become an increasingly contentious public issue in some areas, with vigorous debates taking place in communities that are considering fluoridation, and in some cases, activists attempting to overturn existing fluoridation programs.

On one side of the issue are pro-fluoridation scientists -- along with dental professionals and public health officials - who insist that fluoridation of a water supply is generally safe. Their position is that water fluoridation -- along with the use of fluoride toothpastes and mouth rinses -- can significantly reduce the prevalence of cavities. (1) According to the American Dental Association (ADA), water fluoridation reduces tooth decay by 20 to 40 percent. Fluoridation proponents claim that the only significant negative consequence of fluoridation is the risk of dental fluorosis, a discoloration of tooth enamel that occurs with higher rates of exposure to fluoride, and is not a health risk, only a cosmetic issue.

Dental fluorosis is estimated to affect somewhat less than one-fourth of the population aged 6 to 49. (3) The linkage between fluoride levels and fluorosis were studied, to determine what levels of fluoride exposure would minimize or eliminate this side effect. In 2006, a National Research Council committee of 12 members unanimously recommended that the maximum level of 4 mg/L fluoride concentration in water supplies be lowered.

Subsequently, the World Health Organization established a guideline of a maximum concentration level of 1.5 mg/L of fluoride in drinking water as a way to avoid fluorosis. (4)

Opponents of fluoride claim that fluoride's benefits are outweighed by a list of health risks that go beyond fluorosis. They claim that fluoride's cavity-fighting benefits are questionable, that the research is inconclusive (or even compromised by dental industry influence). The opponents also claim that cavity-fighting results from topical exposure and that ingestion of fluoride is not necessary. They claim that excess exposure cannot be avoided when fluoride is in the water supply and that this exposure over time allows fluoride to accumulate in the body, where it may damage the brain, lower IQ, have neurotoxic effects, and damage bone, among many other health effects. (5)

One of the most controversial issues is the impact of fluoride on the thyroid gland. Many people are not aware that in the first half of the 20th century, fluoride was used medically as an anti-thyroid drug, to slow down the thyroid function in hyperthyroid patients.

Fluoride was found to be effective at suppressing or reducing thyroid function, according to research, and the dose needed to reduce thyroid function was low -- 2 to 5 mg per day over a period of months. (6)

Opponents of water fluoridation are concerned that the levels of fluoride used to treat an overactive thyroid are in the same range of exposure (1.6 to 6.6 mg/day) that is estimated in people living in communities with fluoridated water supplies.

While a number of studies have not found any link between fluoride and thyroid disease, other studies (7) have found that fluoride can cause alterations in the thyroid, including

  • reduced T3 levels
  • increased TSH levels
  • thyroid enlargement (goiter)

What Should Thyroid Patients Do?

The debate over fluoridation has raged for more than 50 years and is likely to continue into the future. With competing studies and inconclusive findings on both sides, it's clear that the debate over fluoridation's impact on thyroid health will continue for decades to come, as experts on both sides of the issue point to research that supports their positions and objectives.

In the meantime, what should thyroid patients do?

As a start, you can stay informed. For pro-fluoride information, a good starting point is the American Dental Association's Fluoride and Fluoridation page. One of the best sources of information regarding the opposition to fluoridation is the Fluoride Action Alert, led by Dr. Paul Connett.

Certainly, thyroid patients have the option to follow the ADA and Centers for Disease Control (CDC) recommendations, and continue to consume fluoridated water, and use fluoridated dental products.

At minimum, however, it's important to be aware of the CDC's warning against overuse of infant formula that is reconstituted with fluoridated water. According to the CDC, if that is a child's sole source of nutrition, "there may be an increased chance for mild dental fluorosis. To lessen this chance, parents can use low-fluoride bottled water some of the time to mix infant formula; these bottled waters are labeled as de-ionized, purified, demineralized, or distilled." (8)

You also may want to determine how much fluoride is in your water supply. A handy link to the CDC database, Fluoride Finder, can help you determine fluoride levels in your county.

For those who feel that the concerns raised by opponents are valid, Richard Shames, MD, author of a number of books on thyroid disease, and a Harvard-trained integrative physician, has said:

We know that 4 or 5 mg per day of fluoride is too much, but the problem is that no one knows how much people are actually getting. Those who exercise and drink a lot of water, bathe frequently, swim in pools, etc. or use fluoridated toothpaste or mouthrinses, may be overexposed to fluoride without realizing it. The first step to take is to stop drinking fluoridated water. You will need more than the standard carbon cannister water filters for this purpose. Instead, you will need a reverse osmosis or distillation unit. I also suggest non-fluoridated toothpaste, which is easily available with a bit of looking carefully at the health food store shelf. I realize that it is possible that children not using fluoride could possibly have more cavities, but this has not been proven to every doctor's satisfaction. I personally believe that the benefits of fluoride, even for children, have been overstated, and the risks minimized. For those who feel a need to use fluoridated products for their children's teeth, as with many health matters, moderation is the key. Use it sparingly and under close supervision, and do not allow children to swallow products containing fluoride.


(1) Petersen, P. et. al., "Effective use of fluorides for the prevention of dental caries in the 21st century: the WHO approach," Community Dentistry and Oral Epidemiology, Volume 32, Issue 5, pages 319-321, October 2004, Abstract
(2) American Dental Association, "Flouride & Fluoridation," Fact Sheet, www.ada.org
(3) Beltrán-Aguilar, E. et. al."Prevalence and Severity of Dental Fluorosis in the United States, 1999-2004," NCHS Data Brief, Number 53, November 2010, Online
(4) Fagin D,"Second thoughts about fluoride". Scientific American 298 (1): 74-81. January 2008
(5) Connett, Paul, "50 Reasons to Oppose Fluoridation, September 2012," Fluoride Action Network, Online
(6) Galletti P, et. al. 1958. "Effect of fluorine on thyroidal iodine metabolism in hyperthyroidism. Journal of Clinical Endocrinology," 18(10):1102-1110. 1958
(7) Susheela AK, et al. "Excess fluoride ingestion and thyroid hormone derangements in children living in New Delhi, India." Fluoride, 38:98-108. 2005. National Research Council. "Fluoride in drinking water: a scientific review of EPA's standards." National Academies Press, Washington D.C. 2006.
(8) "Overview: Infant Formula and Fluorosis," Centers for Disease Control and Prevention, Online
(9) Shames, Richard, MD. "Why We Changed Our Minds About Water Fluoridation," About.com

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