Written by: Tennant Products Editorial Team
Reviewed by: Patsy Scott, CHN (Certified Holistic Nutritionist)
Last Updated: February 2026
TL;DR
- Chlorine, fluorine, and bromine compete with iodine and can displace it in the body.
- This interference may reduce proper thyroid hormone function.
- These elements are commonly found in treated water and some bakery products.
- Taking iodine with chlorinated water may reduce its effectiveness.
- Using filtered water and avoiding brominated or fluoridated products may help support iodine use.
We get this question often:
"Why do I need to take my Iodine supplement
with filtered (non chlorinated) water?"
In this blog we want to share with you the "why" but also help you understand a few more things you need to be sure to consider when taking an iodine supplement, or eating iodine-rich foods to improve your iodine levels.
How Do Chlorine, Fluorine, and Bromine Affect Iodine in the Body
Chlorinated water, bakery products, flame retardants and other dietary and environmental issues reduce our body’s ability to use iodine. WHY?
Chlorine, Fluorine and Bromine compete with iodine in the body.
On the periodic table of elements, iodine is in a group called the Halogens. Fluorine, Chlorine and Bromine are in the same Halogen family.
Iodine is lower on the table, which means that the elements above
iodine in the Halogens group are much more reactive.
Fluorine, Chlorine and Bromine compete with and displace iodine. They are all more reactive than iodine. They are more electronegative than iodine, so they will take binding sites first and even displace iodine that has already attached to the receptor.
Why Is Halogen Competition Important for Thyroid Function
Fluorine, Chlorine and Bromine compete very strongly with iodine. Chlorine and Fluorine are in our water. Bakery products and carpets are now very high in Bromine. Chlorine, Bromine and Fluorine compete with iodine-binding sites on the thyroid hormone. When this occurs, the thyroid hormone does not function as it does when iodine is in place. It creates a state of thyroid deficiency called secondary hypothyroidism.
Even though you may have adequate thyroid hormone levels according to test results, if it is brominated (meaning the iodine-binding sites have bromine instead of iodine), the thyroid hormones do not work like they should! Chlorine and Fluorine in water also compete with iodine and replicate the above situation. Hypothyroidism leads to many serious health issues, including obesity.
Fortunately, iodine supplementation can help increase urinary excretion of Fluorine, Chlorine and Bromine. These elements—Fluorine, Chlorine and Bromine—are toxic to our bodies. Take care to drink pure water and eat non-brominated bread in order to significantly decrease your toxic exposure.
What Should You Avoid When Taking an Iodine Supplement
So now you know why you want to be sure that you are not taking an iodine supplement with chlorinated water. Make sure you are taking it with filtered water.
If you are not already using toothpaste that is fluoride-free, consider switching your toothpaste.
If you choose to be extra careful, you may also want to consider finding bakery products that are organic and Potassium Bromate free.
Want to Learn More? Check out our Educational Materials:
Iodine: The Controversy (41 min Video)
Understanding Lugol's Iodine (27 min Video)
Guide to Taking Dr. Tennant's® Lugol's Iodine Liquid & Capsules
[Free Download]
FAQs
Why should I take iodine with filtered (non-chlorinated) water?
Chlorine can compete with iodine in the body because they belong to the same halogen group. Since chlorine is more reactive, it may displace iodine at important binding sites. Taking iodine with filtered water may help reduce this interference.
How do chlorine, fluorine, and bromine interfere with iodine in the body?
These elements are more reactive than iodine and can compete for the same receptor binding sites. When they replace iodine, thyroid hormone may not function as it should. This can affect how effectively the body uses iodine.
What is secondary hypothyroidism?
Secondary hypothyroidism refers to a state where thyroid hormones do not function properly because iodine-binding sites are occupied by bromine or other halogens. Even if lab results show normal hormone levels, the hormones may not work efficiently. This reduced function can contribute to various health concerns.
Where are chlorine, fluorine, and bromine commonly found?
Chlorine and fluorine are commonly present in treated water. Bromine can be found in certain bakery products, carpets, and other environmental sources. Regular exposure may increase competition with iodine in the body.
Can iodine supplementation help reduce halogen toxicity?
Iodine supplementation may support the urinary excretion of fluorine, chlorine, and bromine. These elements are considered toxic to the body. Reducing exposure while maintaining adequate iodine intake may help limit their effects.
Featured Products in This Article:
Dr. Tennant’s® Logol's Iodine Liquid
A great solution for supporting the body’s need for iodine and iodide. Iodine is one of the few elements required for cellular health that the body cannot produce, so it needs to be supplemented through food or additional nutrition.
Dr. Tennant’s® Lugol's Iodine Plus Capsules
A complete iodine supplement solution with necessary co-factors Zinc, Selenium, B1 as well as Vitamin C necessary for proper iodine metabolism.
