T3 is a vital hormone; it controls your metabolism, body temperature, and heart rate. But there can be too much of a good thing. High T3 levels can increase your risk for pregnancy complications, liver disease, and can even reduce your sex drive. Find out the common causes of high T3 levels and what you can do to improve them.
What is T3?
T3, short for triiodothyronine, is a hormone that is produced by your thyroid. It has a variety of functions in your body, like regulating your heart rate, body temperature, and metabolism .
The other main hormone made by your thyroid is T4, which acts as a precursor to T3. Your cells can convert T4 into T3 as needed. While T4 does have some biological activity, T3 is about four times more active and does most of the work in your body .
High T3 levels are usually a sign of hyperthyroidism, a condition where the thyroid produces too much thyroid hormone. In this article, we’ll list out some of the major causes of high T3 and the health risks associated with them .
You can also learn much more about T3 and T4 in our thyroid hormone article here.
Causes of High T3
1) Graves’ Disease
Graves’ disease is an autoimmune disorder where the body mistakenly produces antibodies that can bind to the TSH receptor. This binding will stimulate the TSH receptor, leading to an overproduction of thyroid hormones. In the U.S., Graves’ disease is the most common cause of hyperthyroidism, accounting for about 50-80% of cases .
The symptoms of Graves’ disease are similar to other hyperthyroidism conditions and can include hand tremors, trouble sleeping, intolerance to heat, and weight loss. Graves’ disease can also cause Graves’ ophthalmopathy, an eye disease that causes eye-bulging and lid retraction .
Treatment of this condition usually involves antithyroid drugs (like methimazole), radioactive iodine, or surgery to remove all or parts of the thyroid. Eye symptoms are usually treated with eye drops or surgery in severe cases .
2) Thyroid Tumors
Thyroid tumors (also known as thyroid adenomas) are benign tumors of the thyroid gland. They are often described as “hot” or “cold”. A “cold” thyroid tumor is inactive and does not produce any thyroid hormone. On the other hand, a “hot” tumor is active and produces T3 and T4, which can lead to hyperthyroidism .
In some parts of the world, thyroid tumors account for almost 50% of all cases of hyperthyroidism. However, if the tumor is not causing any negative effects, the doctor may decide to simply monitor the condition. Otherwise, the tumor can be surgically removed .
A goiter simply means an enlarged thyroid gland. The most common cause of goiter is iodine deficiency, but many other factors like inflammation can contribute to this enlargement .
Most of the time, a goiter is benign and does not cause any ill effects. In some cases, small nodules can form on the enlarged thyroid which can produce T3 and T4. The release of thyroid hormones from these nodules can lead to hyperthyroidism. Treatment usually involves antithyroid drugs, radioactive iodine, or surgery .
Thyroid hormone levels naturally increase during pregnancy because the mother must also supply T3 and T4 to the developing baby. The body normally does this by increasing levels of hCG, a hormone produced by the placenta that can bind to TSH receptors, which produces more thyroid hormones [7, 8].
T3 and T4 levels increase significantly in the 1st trimester of pregnancy and gradually decline during the 2nd and 3rd trimesters. Levels should return to normal within 1-2 months after giving birth [7, 8].
On rare occasions, thyroid levels can increase too much during pregnancy, causing hyperthyroidism. This usually happens when the mother also has another condition that affects the thyroid, such as Graves’ disease [7, 8].
5) High Iodine Intake
In many parts of the world, people do not receive enough iodine in their diet, which can lead to high rates of hypothyroidism. That is why iodine is commonly added to salt, making iodized salt, to help improve intake .
However, it is possible to consume too much iodine, which can lead to hyperthyroidism in rare cases. The recommended upper limit of iodine is 1100 micrograms. Excessive amounts of iodine supplements or high-iodine foods (like seaweed or fish) can potentially lead to hyperthyroidism. Those with thyroid nodules are more at risk, according to research [10, 11].
6) Exposure to Toxic Metals
Certain heavy metals can be toxic to humans. Cadmium, in particular, can disrupt the body’s balance of thyroid hormones .
Research suggests that exposure to even low levels of cadmium can cause the thyroid gland to become hyperactive and secrete more T3 and T4. Cadmium exposure is also linked to thyroid tumors, which further increase the levels of thyroid hormones [12, 13].
Several medications can increase the level of thyroid hormones in your blood.
The most obvious example would be thyroid medications that are used to treat low thyroid levels (hypothyroidism). For example, desiccated thyroid (Armour Thyroid) is a drug that contains T3 and T4 extracted from animals. Taking an excessive amount of these drugs can cause thyroid hormone levels to become too high [14, 15].
- Amiodarone, used to treat irregular heartbeats
- Interferon alpha, used to treat various cancers
- Human growth hormones (somatotropin)
Possible Health Risks of High T3
1) Hyperthyroidism Symptoms
If your T3 levels are too high, you may experience hyperthyroid symptoms. Symptoms can vary greatly depending on age, the severity of the disease, and the presence of other conditions. The most common symptoms of hyperthyroidism include :
2) Thyroid Storm
Hyperthyroidism can also sometimes lead to thyroid storm, a life-threatening condition that is usually triggered by another serious illness, such as fever, infection, or a heart attack. Those with uncontrolled hyperthyroidism and those who abruptly stop their antithyroid medications are more at risk .
Thyroid storm is essentially a severe form of hyperthyroidism and shares many of the same symptoms. However, a thyroid storm can also cause fever, confusion, heart attack, and jaundice (yellowing of the skin and eyes). This condition requires immediate medical attention .
3) Pregnancy Complications
High levels of thyroid hormones can be dangerous for both the mother and baby. For example, women with uncontrolled hyperthyroidism are about 9 times more likely to have a low birth weight pregnancy and are almost 17 times more likely to give birth prematurely [19, 8].
- Preeclampsia, a form of high blood pressure that can occur in pregnant women
- Heart failure
- Thyroid storm
- Birth defects
- Hyperthyroidism in the baby
- Low birth weight
As you can see, proper control of your thyroid hormones is critical during pregnancy. Dosing requirements for thyroid medications often change while pregnant. Always speak with your doctor if you plan to become pregnant or are pregnant and have high thyroid hormone levels .
4) Metabolic Syndrome
Metabolic syndrome refers to a collection of disorders that includes obesity, high blood pressure, high blood sugar, high blood triglycerides (fats), and low HDL (your good cholesterol). People with three or more of these conditions are considered to have metabolic syndrome .
One study of 245 people who do not have hyperthyroidism found that those with higher free T3 levels (3.37–4.12 pg/mL) are about twice as likely to have metabolic syndrome than those with lower levels (2.32–2.96 pg/mL). Interestingly enough, everyone in the study had free T3 levels that are considered normal (2.0-4.4 pg/mL) . More work will be needed to the relationship of high T3 levels with metabolic syndrome but this initial study was very interesting.
5) High Cholesterol
Thyroid hormones play a big role in metabolism, which includes regulating cholesterol levels. A study looked at the connection between thyroid hormones and cholesterol levels in 296 elderly patients who have diabetes, but normal thyroid function .
Researchers found that higher free T3 levels correlate to higher total cholesterol and LDL (the bad kind of cholesterol). However, the opposite was true with T4; higher free T4 levels are linked to lower levels of total cholesterol and LDL .
6) Liver Disease
Non-alcoholic fatty liver disease (NAFLD) describes the buildup of fat in the liver that is not caused by alcohol consumption. This condition increases the risk of other liver diseases, including cirrhosis, liver cancer, and liver failure .
According to a study of 2576 people with normal thyroid function, high free T3 levels are linked to higher rates of NAFLD. This association was not seen with free T4 or TSH .
7) Sexual Dysfunction
Men are at risk as well. Two studies with over 3000 men each found that hyperthyroidism increases the risk of severe erectile dysfunction .
Ways to Improve T3 Levels
What can you do if your T3 levels are too high? The first step is talking to your doctor. High thyroid hormone levels are most commonly caused by thyroid disorders that require medical attention. Treatment may include antithyroid medications, radioactive iodine, or surgery to remove part or all of your thyroid .
- Seafood, such as fish, shrimp, and shellfish
- Dairy products
- Bread and cereal
- Iodized salt
There is also limited evidence that some supplements may help decrease T3 levels, including:
Talk with your doctor before starting any supplements as they may have interactions with your medications.
This post is part of a series about thyroid hormones. Read the other parts to learn about:
- T3 Test Blood Test + Normal Levels
- All You Need to Know About Thyroid Hormones (T3 & T4)
- Top 12 Surprising Factors That Decrease Thyroid Hormones
- Low T3 / Euthyroid Sick Syndrome Symptoms & Causes
- Reverse T3 Test: Low & High Levels + How to Fix them
- TSH Blood Test: Normal Levels & Range
Irregular T3 Levels?
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High T3 levels are most commonly caused by thyroid disorders like Graves’ disease, goiter, and thyroid tumors. Health risks of high T3 include pregnancy complications, high cholesterol, liver disease, and sexual dysfunction.
Lowering T3 levels usually involves treating the underlying condition, which requires medical attention. Limiting your iodine intake can also help control levels.