Fluoride is harmful to the body and to your thyroid function. Several studies indicate that too much fluoride causes hypothyroidism. In this article, I explain how you are exposed to fluoride in daily life and why it is so important to limit your exposure.
The Toxicity of Fluoride
Even though fluoride can improve dental health when applied topically, ingesting too much fluoride is harmful to the body because it is toxic to cells and organs — and especially to the thyroid gland. Research on populations consuming fluoridated water at just 1 ppm (1 mg/L) has shown adverse effects on the nervous system, enzymes, immune system, DNA, reproductive system, kidneys, heart, and digestive tract. Several studies also indicate that excess fluoride intake causes hypothyroidism.
Fluoride also damages the parathyroid gland, which sits close to the thyroid gland at the front of the neck. Too much fluoride can lead to hyperparathyroidism — the uncontrolled secretion of parathyroid hormone — resulting in chronic inflammation, disruption of calcium metabolism, and osteoporosis — processes that the lifestyle and hormonal strategies in my Hormone Rebalance Intensive™ course and the broader method in my book Roadmap to Metabolic Health help address.
Am I Exposed to Fluoride?
Most people are exposed to fluoride every day without realising it. Fluoride is added to toothpaste, and some countries also fluoridate their water supply to promote dental health. Certain medications contain fluoride as well. In addition, some foods are naturally high in fluoride.
Why Fluoride Harms Thyroid Function
Iodine is an essential element for thyroid hormone production, and fluoride interferes with how iodine works in the body. The thyroid gland produces two hormones that both contain iodine: thyroxine (T4), which contains four iodine atoms, and liothyronine (T3), the active thyroid hormone, which contains three iodine atoms. The names T3 and T4 come directly from the number of iodine atoms in each molecule — which underscores how central iodine is to thyroid function.
Fluoride and iodine are structurally very similar, as both belong to the same group in the periodic table. Fluoride can block the active transport of iodide into the thyroid gland by occupying the receptors that iodine normally uses. In this way, fluoride disrupts the formation of T3 and T4, leading to hypothyroidism.
Can Iodine Protect Against Fluoride?
Because fluoride displaces iodine, one might think that an iodine supplement would offer protection against fluoride toxicity and help support thyroid function. For a careful guide to which supplements genuinely support thyroid health, see my Supplement Solutions course. However, according to Dr. Ray Peat, iodine supplements are almost always the wrong approach. Overdosing on iodine can trigger inflammation in the thyroid gland, which itself leads to hypothyroidism. Getting iodine from food is therefore the safer strategy.
In my Thyroid Recovery & Renewal™, I cover which iodine-rich foods to include in your diet to support thyroid function with the right amount of iodine — without the risks of supplementation.
Fluoride in Toothpaste
Ionised fluoride compounds such as sodium fluoride (NaF) are used for cavity prevention and are added to toothpaste, mouthwashes, and other dental products. To protect your thyroid gland from daily fluoride exposure, I recommend switching to a fluoride-free toothpaste and avoiding other dental products that contain fluoride.
Fluoride in Medication
Fluoride is also found in some medications, usually in the form of an organic carbon-fluoride bond called organofluorine. In most cases, this bond is strong enough to resist breaking down into free fluoride within the body — but this is not always so. Research has found that some fluorinated drugs do break down and release fluoride. I recommend reading the ingredient list of any medication carefully and, where possible, choosing alternatives that do not contain any form of fluoride.
Fluoride in Drinking Water
Some countries add fluoride to their water supply to promote dental health. The naturally occurring level of fluoride in water is typically around 0.5 mg/L. Some researchers consider fluoride levels above 0.3 mg/L — or even 0.2 mg/L — to be unsafe. However, fluoridated water supplies can contain anywhere from 0.7 to 1.3 mg/L.
Most countries in the European Union do not add fluoride to drinking water, while most communities in the United States continue to fluoridate their supply. According to Dr. Ray Peat, drinking fluoridated water poses a serious risk to thyroid function and general health. Even if fluoride is not deliberately added to your supply, your tap water may still have a naturally high fluoride content. I recommend contacting your local water authority to find out the fluoride level in your area.
Can Fluoride Be Removed from Water?
Yes — water purification can effectively remove fluoride. Reverse osmosis systems and water distillation both work well. A good defluorination system should achieve at least 80 percent fluoride removal to be considered adequate. Importantly, standard activated carbon filters sold for home use do not remove fluoride.
Foods High in Fluoride
Certain foods are naturally very high in fluoride, and it is worth being aware of them. Black and red rock salt can contain significant amounts of fluoride, as well as other impurities such as iron, which is why I do not include it in my pro-metabolic dietary recommendations. Black tea is also naturally high in fluoride — making coffee a better daily choice. Fortunately, coffee also has many well-documented benefits for thyroid function and metabolic health.
How Diet Can Protect Against Fluoride Toxicity
The most important steps you can take are avoiding fluoridated water and switching to fluoride-free toothpaste. Replacing black tea with coffee is another simple way to reduce your daily fluoride load. Beyond that, it is important to eat a diet rich in calcium, vitamin D, antioxidants, and trace minerals — all of which help the body defend against the toxic effects of fluoride.
My dietary approach is based on the research of Dr. Ray Peat, and the pro-metabolic way of eating naturally provides the nutrients that protect against fluoride toxicity. If you want a complete guide to thyroid-friendly eating — including iodine-rich foods, mineral support, and pro-metabolic dietary principles — I cover all of this in depth in my book How to Boost Metabolism with Food and in my Metabolic Nutrition Mastery™.
For a broader foundation in pro-metabolic health, thyroid recovery, and the principles I use with my clients, I also recommend exploring my Healing Metabolism book series — a step-by-step resource covering metabolism, thyroid function, testing, and treatment.
Frequently Asked Questions
How does fluoride affect thyroid function?
Fluoride and iodine belong to the same group in the periodic table (halogens), meaning fluoride can displace iodine in the body. Fluoride competes for the same receptors that transport iodine into the thyroid gland. By blocking iodine uptake, fluoride disrupts the production of thyroid hormones T3 and T4, potentially leading to hypothyroidism — something I cover in depth in my book How to Use Thyroid Medication and my Thyroid Recovery & Renewal course.
Is fluoride in toothpaste bad for your thyroid?
Yes, ingested fluoride — even small amounts from toothpaste that is swallowed — contributes to overall fluoride load in the body. I recommend switching to a fluoride-free toothpaste to reduce thyroid exposure. There are many effective fluoride-free alternatives available.
Does fluoride in drinking water cause hypothyroidism?
Several studies have found associations between water fluoridation and increased rates of hypothyroidism in the population. Research on populations consuming fluoridated water at just 1 ppm showed adverse effects on multiple organ systems, including the thyroid. I recommend checking your local water fluoride level and using reverse osmosis filtration if levels are elevated.
Can iodine supplements protect against fluoride toxicity?
While the logic seems sound — iodine could theoretically counteract fluoride displacement — Dr. Ray Peat strongly advised against iodine supplementation. Excess supplemental iodine can trigger thyroid inflammation and actually worsen hypothyroidism. Getting iodine from whole foods (dairy, eggs, seafood) is the safer approach. I cover safe supplementation strategies in my Nutritional Supplements course.
What is the best fluoride-free toothpaste?
Look for toothpastes that use hydroxyapatite, baking soda, or herbal formulas as alternatives to fluoride. These can provide effective dental care without the fluoride exposure that disrupts thyroid function.
