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Fluoride Exposure and Thyroid, Kidney and Liver Function

Over 200 million people experience fluoride exposure every day. Does it affect the thyroid gland or impact kidney function in adolescents?

According to the CDC, nearly 3/4 of the American population on “community water systems” have fluoride exposure from their water. That’s more than 200 million people. Growing up ,I remember hearing radio commentators complaining that putting fluoride in the water supply was a Communist plot. Most health professionals maintained that anti-fluoride sentiment was ridiculous and that fluoride was a great public health boon that would protect people from tooth decay. I have never taken a stand on fluoridation, but this reader asks an interesting question about fluoride in the water and thyroid function.

Can Fluoride Exposure Affect the Thyroid?

Q. I have Hashimoto’s autoimmune hypothyroid disease. I did not feel well taking just Synthroid. When I started taking Unithroid along with a small dose of Cytomel, that worked much better for me.

Most doctors only test the TSH level and then treat that number. Testing free T4 and free T3 is a much better indicator of real thyroid activity.
I have heard that fluoride has a negative effect on the thyroid. Is that true?

A. Fluoride remains a controversial water treatment. On the one hand, dentists promote the use of fluoridated water and toothpaste to prevent tooth decay.

On the other hand, some data link high fluoride exposure to an increased risk for hypothyroidism.

A systematic analysis of 10 studies concluded (Indian Journal of Dental Research, May-June, 2018):

“The study has shown a positive correlation between fluoride and hypothyroidism, which is an alarming issue.”

A recent study from Canada found that (Science of the Total Environment, April 15, 2023):

“In this Canadian pregnancy and birth cohort, fluoride in drinking water was associated with risk of primary hypothyroidism in pregnant women.”

Scientists believe that fluoride may interfere with the deiodinase enzymes that convert inactive T4 hormone to active T3. To learn why the conversion of T4 to T3 is so critical to thyroid health, here is a link you will appreciate.

Research on Fluoride Exposure a Third Rail Issue?

I am somewhat surprised that there hasn’t been more research in the United States about the impact of thyroid exposure on our physiology and biochemistry. I suspect that once most of our community water systems were fluoridated, scientists did not want to rock the boat. That’s not to say there is a problem, but much of the toxicological research has been done abroad.

For example, Polish researchers writing in the journal Chemosphere (Dec. 2020) offer this perspective:

“The effects of fluoride on endocrine tissues has not been sufficiently explored to date. The current body of knowledge suggest significant effects of that mineral on reducing sex hormone levels, which may consequently impair fertility and disrupt puberty. The majority of studies confirm that sodium fluoride increases TSH levels and decreases the concentrations of T3 and T4 produced by the thyroid.”

Fluoride Exposure and Adolescents:

A study has raised questions about the safety of fluoride exposure, especially for adolescents (Environment International, Aug. 8, 2019). This is one of those chicken-or-egg-kind of studies. Fluoride may affect both kidney and liver function but altered kidney and/or liver function may impact absorption of fluoride. Which comes first?

Fluoride Exposure and Kidney and Liver Function:

Scientists used data from the National Health and Nutrition Examination Survey [NHANES] on nearly 2,000 adolescents who had blood levels of fluoride measured. In addition, 1,742 teens in the study had measurements of fluoride in their household tap water.

None of the young people had kidney disease, but measurements of their kidney and liver function were worrisome. Those with the highest blood levels of fluoride had lower kidney function. A similar association was found for those whose household water was high in fluoride.

In Their Own Words:

The authors of this study share the chicken-or-egg analysis:

“Higher plasma fluoride concentrations were associated with changes in kidney and liver related parameters.

“Given the cross-sectional nature of this study, there are several possible interpretations for the findings. First, fluoride exposure may contribute to complex changes in kidney and liver parameters among U.S. adolescents. This possibility is supported by the consistency of our findings with research demonstrating a dose-response relationship between water fluoride levels above 2 mg/L and enzyme markers of liver and kidney dysfunction… Chronic low-level fluoride exposure is also associated with decreased thyroid gland activity among children and adults… Thus, fluoride exposure could potentially compromise kidney function via glomerular damage, or indirectly via suppression of the thyroid gland.”

“An alternative interpretation for our findings is that poorer kidney function may contribute to increased plasma fluoride levels rather than resulting from them.”

Making Sense of Medical Mystification:

In other words, does fluoride exposure cause changes in liver and kidney function or does “poorer kidney function” lead to higher levels of fluoride circulating in the body? The authors offer a third possibility. Fluoride exposure could impair kidney function which leads to diminished excretion of fluoride which in turn increases absorption of fluoride which then leads to poorer kidney function. Chicken-egg-chicken or, if you prefer, egg-chicken-egg!

What Should We Conclude from This Research?

Here’s what we do know:

  1. Research on animals demonstrates that fluoride, even at relatively low levels, can be toxic to liver and kidneys.
  2. Kidneys and livers accumulate fluoride in humans.
  3. Fluoride research in humans is limited. Nevertheless, there are data hinting that fluoride exposure is associated with kidney and liver toxicity.
  4. Fluoride exposure affects thyroid function, which could indirectly impact kidney function.

What We Don’t Know:

  1. Does fluoride cause altered kidney function or does altered kidney function increase fluoride absorption?
  2. Does fluoride exposure affect kidney function in younger children?
  3. Are otherwise healthy adults impacted by exposure to higher levels of fluoride?
  4. Are people with reduced kidney or liver function more susceptible to toxicity from fluoride?

Next Steps?

We find it shocking that after 70+ years we do not have answers to these important questions.

The authors of this study suggest that:

“further studies are needed to examine the mechanisms by which chronic low-level fluoride exposure may impact kidney and liver related parameters during development and adolescent life stages…”

We couldn’t agree more, but we wish those studies had been done before tens of millions of people were exposed to chronic low levels of fluoride.

Read more about new research regarding fluoride exposure and IQ at this link.

Please share your thoughts in the comment section.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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  • Malin, A.J., et al, “Fluoride exposure and kidney and liver function among adolescents in the United States: NHANES, 2013–2016,” Environment International, online, Aug. 8, 2019, https://doi.org/10.1016/j.envint.2019.105012
  • Hall, M, et al, "Fluoride exposure and hypothyroidism in a Canadian pregnancy cohort," The Science of the Total Environment," April 15, 2023, doi: 10.1016/j.scitotenv.2022.161149
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