The modern world is full of toxic chemicals that don't belong in our bodies. These include heavy metals such as mercury, cadmium and lead, persistent organic pollutants (POPs) such as PCB, dioxins, pharmaceutical drugs and other toxins. Although avoidance is always the best way to protect oneself, at this point our environment is polluted with so many toxins, everyone is effected. For examples, over 80,000 POPs that have been released into the environment. For many of these we lack of information on how they affect human health. . Therefore detoxification is an essential part of maintaining health in the 21st century.
The total effect of such toxicity is beyond the scope of this article. We will only discuss the effect of toxins on thyroid functions, but this is only a small part of total toxic load we all are under.
Many people are familiar with some of the most well-known POPs, such as PCBs, DDT, and dioxins. POPs include a range of substances that include:
Intentionally produced chemicals currently or once used in agriculture, disease control, manufacturing, or industrial processes. Examples include PCBs, which have been useful in a variety of industrial applications (e.g., in electrical transformers and large capacitors, as hydraulic and heat exchange fluids, and as additives to paints and lubricants) and DDT, which is still used to control mosquitoes that carry malaria in some parts of the world.
Unintentionally produced chemicals, such as dioxins, that result from industrial processes and from combustion (for example, municipal and medical waste incineration and backyard burning of trash). 
Persistent organic pollutants decrease both the production and conversion thyroid hormone. Dioxins, PCB's and oregano compounds have also been shown to interfere with the action of thyroid hormone. Therefore, even if you have the right amount of active T3, toxins may prevent T3 from doing anything. This may produce symptoms of hypothyroidism as well, despite perfect thyroid hormone levels. 
So if we go back to the thyroid hormone family chart we can see that POP's interfere with thyroid hormone production, conversion, and usage.
Considering the number of prescription medications that can interfere with thyroid function, I suggest it's best for patients to research any drug they are prescribed to see if there is a possible connection with hypothyroidism symptoms. The drugs listed above are just a sample, not a comprehensive review of medications that interfere with thyroid function.
Heavy metals such as lead, cadmium and mercury can affect thyroid function in several ways. Lead and mercury will directly stop the thyroid gland from making hormone. These toxins damage the liver health. And as we are about to see, liver health is essential to thyroid hormone function. 
The liver is a large organ on the right side of the body, just under the rib cage. It has many functions, but perhaps it's biggest job is to take toxins (such as heavy metals and POPs) and convert them into chemicals that can be eliminated from the body.
In addition to it's role in detoxification, most of the conversion of T4 into T3 happens in the liver.  In fact, the liver and another major organ of detoxification, the kidneys, have been estimated to be responsible for up to 80% of the conversion of T4 to T3.  Therefore, poor liver function can be bad for thyroid hormone in two ways:
Poor liver function is not the same as liver disease . In liver disease such as hepatitis cirrhosis, actual liver tissue is damaged and destroyed. Common tests doctors run for liver disease are ALT and AST. ALT and AST are enzymes that are spilled into the blood stream when liver cells dies. Since the liver is always regenerating itself, there is always going to be some cell death, and these test will not be zero. But when ALT or AST are up, it means that something is killing liver cells faster than usual. .
Poor liver function means the liver is not doing it's job well, so toxins are not being eliminated from the body. Causes of poor liver function could include liver disease, but also nutritional deficiencies, sluggish bile, and just simply being overwhelmed by too many toxins.
A detoxification program or a "detox," as it is more commonly called is a protocol for eliminating toxins from the body. There are countless books and web sites promoting their detox program, and the one everyone should do. Some of these programs are very good, and others are horrible. The two I warn clients about are:
Our fat cells are not just a place of stored fuel. Fat stores toxins. When we to loose weight and burn off fat, these toxins are released into the blood stream. It has been shown that weight loss can increase the levels of pesticides in the blood, and decreases levels of active T3. Therefore, detoxification should always be a consideration with weight loss programs. This is especially true is there is a history of hypothyroidism symptoms. [79 ]Detox programs are also an excellent way to rid the body of excess estrogens. Synthetic plastics and other chemicals are powerful fake estrogens, which are much stronger than the real estrogen your body makes. An increase in these estrogens decreases the function of thyroid hormone. Detoxification is the first think I do to reduce the load of synthetic estrogens on the body. This will be discussed in more detail in section 15.
Of all the detox programs out there, the one I like to see people do the most, is working with a holistic health care professional. This can be a naturopathic doctor like myself, a nutritionist, nutritionally minded chiropractor, Chinese medicine doctor, holistic MD, or others in this field
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