Canadian study: more evidence that fluoride damages the thyroid

This large Canadian study is especially relevant to Australia and New Zealand where iodine deficiency is common.

"I have grave concerns about the health effects of fluoride exposure. And not just from my study but the other studies that have come out in recent years."

Ashley Malin, Lead Author

The results of this study titled “Fluoride Exposure and Thyroid Function Among Adults Living in Canada: Effect modification by iodine status” were recently published in Environment International.1 This study is particularly relevant to Australia because it showed that Canadian adults who are iodine deficient and have higher fluoride exposure are at an increased risk of hypothyroidism.

“While our findings only establish an association, not cause-and-effect, they are important because they suggest a potential effect of fluoride on thyroid function at levels of exposure that are typical for Canadians,” said Christine Till, the study’s senior author and associate professor at York University.

The study used population-based data from a Canadian Health Measures Survey (CHMS) consisting of 6.9 million adults between the ages of 18 and 79 years. Adults who were diagnosed with a thyroid disorder, or who were on thyroid medication, as well as pregnant women, were excluded.

The research team, based out of York University in Toronto, and the Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai in New York, tested whether higher levels of fluoride in urine are associated with disrupted thyroid function in adults living in Canada.

The study found that adults who are iodine deficient and have higher levels of fluoride in their system have a greater risk of an underactive thyroid. In fact 18 per cent of the 6.9 million adults they studied were iodine deficient. That’s potentially around 1.2 million people at risk of an underactive thyroid due to fluoride exposure.

“Prior studies investigating fluoride exposure and thyroid function among adults did not consider iodine status – an important modifying factor,” said lead author, Ashley Malin, post-doctoral fellow at the Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai in New York. “It was particularly important that we considered iodine status in this study because iodine deficiency is relatively common among adults in Canada.”

“Fluoride may interfere with enzymes that contribute to thyroid hormone synthesis and active transport of iodine into the thyroid,” Malin said. “Iodine may also facilitate bodily excretion of fluoride, thereby buffering the thyroid from its potential adverse effects.”

“I have grave concerns about the health effects of fluoride exposure. And not just from my study but the other studies that have come out in recent years.”

“Fluoride may interfere with enzymes that contribute to thyroid hormone synthesis and active transport of iodine into the thyroid. Iodine may also facilitate bodily excretion of fluoride, thereby buffering the thyroid from its potential adverse effects.”

Ashley Malin, Lead Author

Iodine is the basic building block of the T3 and T4 hormones so adequate iodine intake is essential for the proper functioning of the thyroid gland. When iodine intake is inadequate during infancy and early childhood, the child’s brain can suffer permanent damage, including mental retardation. In fact iodine deficiency is a leading cause of mental retardation worldwide. Several research studies also show that fluoride exposure worsens the impact of an iodine deficiency.

In China alone, researchers have repeatedly found that an iodine deficiency coupled with fluoride exposure produces a significantly more damaging effect on neurological development than iodine deficiency alone. The studies showed that an iodine deficiency lowers the threshold at which fluoride damages the brain along with other forms of fluoride toxicity, including dental fluorosis.

This iodine relationship is particularly relevant to Australia and New Zealand where iodine deficiency can be a serious problem. The Australian Thyroid Foundation, a leading education and advocacy organisation on thyroid health provides this relevant information:

“In continents such as Australia and New Zealand, natural iodine levels are very low in the soils where we grow our vegetables, grains and graze livestock. Insufficient iodine in the diet results in a range of conditions known as Iodine Deficiency Disorder (IDD). Iodine deficiency is becoming an increasingly common cause of thyroid health problems in Australia.”

“More than 50% of children and pregnant or breastfeeding women living in Australia have been shown to be iodine deficient, and are at risk of developing thyroid disease.”

There is also evidence to show that iodine uptake is reduced by fluoride. In March 2019, Environmental Scientist Declan Waugh, published a study on the effect of fluoride on iodine absorption.2  “Based on the findings of this study, evidence strongly suggests that F ingestion contributes to pathological states by impairing iodine absorption and diminishing iodine concentrating ability,” Waugh concluded.

“More than 50% of children and pregnant or breastfeeding women living in Australia have been shown to be iodine deficient, and are at risk of developing thyroid disease.”

Australian Thyroid Foundation

There is also evidence to show that iodine uptake is reduced by fluoride. In March 2019, Environmental Scientist Declan Waugh, published a study on the effect of fluoride on iodine absorption.2  “Based on the findings of this study, evidence strongly suggests that F ingestion contributes to pathological states by impairing iodine absorption and diminishing iodine concentrating ability,” Waugh concluded.

 

Reference notes:

  1. Malin AJ, et al, “Fluoride Exposure and Thyroid Function Among Adults Living in Canada: Effect modification by iodine status,” October 2018. PDF available here.
  2. “Fluoride Exposure Induces Inhibition of Sodium/Iodide Symporter (NIS) Contributing to Impaired Iodine Absorption and Iodine Deficiency: Molecular Mechanisms of Inhibition and Implications for Public Health.” Declan T. Waugh, Int. J. Environ. Res. Public Health, March 2019. Available here.