Antonio Bianco is the dean of a medical school and runs a lab focused on understanding the function of thyroid hormone. The goal of his research is to better serve patients with hypothyroidism, a condition caused by insufficient thyroid hormone.

The research examines the hormone's effects at multiple levels. At the tissue level, it explores what the hormone does in organs like the liver and the heart. At the cellular level, the lab studies how thyroid hormone affects the folding of chromatin, which is key to regulating gene expression. The hormone, specifically T3, works by controlling different genes. Since genes are the essence of a cell's function, regulating their expression changes how the cell behaves. This change has important consequences for the entire tissue, the organ, and the body as a whole.

Many people have a basic understanding of the thyroid gland. It is located over the voice box and produces a hormone. This hormone starts in an inactive form, abbreviated as T4 because it has four iodine atoms. Enzymes in the body then remove one of these iodines to create the active form of the hormone, T3.

This active hormone is crucial for regulating many bodily functions, including energy expenditure, body temperature, mood, and sleep. It is not uncommon for individuals to produce an insufficient amount of this hormone, a condition known as hypothyroidism. Consequently, many people take some form of thyroid hormone replacement.

However, managing thyroid conditions is significantly more complex than other endocrine issues, like low testosterone. With testosterone, the symptoms are well-understood, the diagnostic test is simple, and replacement is straightforward. The thyroid system, in contrast, involves more complexity in both diagnosis and treatment, which leads to varied approaches and opinions.

The thyroid gland uses iodine from our diet, found in sources like seafood and iodized salt, to produce its hormones. It acts as a large storage unit for the prohormone T4, which contains four atoms of iodine. The gland slowly releases this T4 into the bloodstream, creating a stable reserve.

However, T4 itself is largely inactive. The crucial step is its conversion into the active hormone, T3, which is achieved by removing just one iodine atom. This small change makes a big difference because cellular receptors have a high affinity for T3 but a very low one for T4. According to Antonio Bianco, this is a conformational issue; T4 simply doesn't fit well into the receptor's pocket.

From an evolutionary standpoint, this entire system is designed to conserve iodine, which was often scarce. By storing the hormone as T4 and recycling the iodine atom released during activation, the body uses iodine very efficiently.

The two hormones also have vastly different lifespans, which is a key part of how the body regulates their effects. T4 has a long half-life of about eight days, while T3's is only about 12 hours. This short duration for the active hormone allows for precise control over tissue exposure.

The contrast is dramatic. T4 has a half life of about 8 days. T3 has a half life of about 12 hours. Once it's activated, it triggers its destruction. It has a brief action. It works potently. However, it's targeted for destruction. It's just metabolized and cleared. And that tells you that this is a way the body has to regulate the action of thyroid hormone.

The body has a sophisticated way to regulate its metabolic rate by choosing how to process the thyroid hormone T4. An enzyme called deiodinase can remove an iodine atom from T4 to create one of two molecules. If it removes an iodine from the outer ring of the T4 molecule, it creates T3, which is highly active. If it removes an iodine from the inner ring, it creates reverse T3, which is essentially inactive. This creates a powerful switch; the body can either activate thyroid hormone by making T3 or inactivate it by making reverse T3, allowing for rapid adjustments to metabolism.

A clear example of this is what happens during fasting. When the body senses a lack of food intake, primarily through low insulin and leptin levels, the hypothalamus signals a need to conserve energy. Antonio Bianco explains the body's logic:

Thyroid hormone accelerates energy expenditure. Thyroid hormone is all about burning energy, burning sugar, burning protein. So the hypothalamus says, 'Well, I have to take my foot off the gas here so that even though there's less food coming in, we're going to reduce the rate at which I'm burning the fuel.'

To achieve this, the body alters the deiodinase pathway. T4 is preferentially converted into inactive reverse T3 instead of active T3. This causes T3 levels to drop and reverse T3 levels to rise, effectively putting the brakes on metabolism. Reverse T3 levels increase for a second reason as well: its clearance from the body slows down. An enzyme in the liver known as D1, which metabolizes reverse T3, becomes less active without carbohydrates and insulin. This combination of increased production and decreased clearance leads to a sharp spike in reverse T3 during a fast.

Because the enzymes themselves cannot be measured from a blood test, the ratio of T3 to reverse T3 can serve as a useful surrogate for this activity. A falling ratio, as seen in fasting, indicates a metabolic shift towards energy conservation.

There are three key enzymes involved in thyroid hormone conversion: D1, D2, and D3. D2 is considered a superb, supercharged enzyme. It has a thousand-fold more affinity for the T4 hormone than D1 does. Outside of the thyroid gland itself, D2 is responsible for producing about 80% of the active T3 hormone. In contrast, D1 is a less efficient enzyme, producing only about 20% of the T3 outside the thyroid. D1 also creates a small amount of reverse T3.

While D1 and D2 primarily activate thyroid hormone, D3 does the opposite; its only function is to inactivate it. D3 takes active T3 and transforms it into T2, an inactive molecule. It also takes T4 and converts it into reverse T3, another inactive molecule. This ensures the T4 doesn't become active. D3 is the primary producer of reverse T3.

Effectively, D2 and D3 are the most powerful enzymes in this process. D2 makes active T3, while D3 eliminates and inactivates thyroid hormone. Both T2 and reverse T3 are considered 'dead' molecules with no biological activity. However, reverse T3 is more useful to measure in a lab. This is because it has a longer half-life of a few hours, whereas T2 has an extremely short half-life. The conversion to reverse T3 is a one-way path; it cannot be turned back into active T3. The body does, however, recycle the iodine from these inactive molecules.

The hypothalamus is the key to thyroid regulation. It produces a hormone called TRH, which signals the pituitary gland to produce TSH. TSH, in turn, stimulates the thyroid gland to function. If the hypothalamus or pituitary is damaged, TSH won't be produced, leading to a condition called central hypothyroidism.

It's a common misconception that TSH levels themselves cause symptoms. TSH is just a signaling hormone. Its job is to stimulate the thyroid gland. The symptoms of thyroid disorders are caused by the amount of thyroid hormone, not the level of TSH.

If a patient shows up and their TSH is 75, the symptoms they feel are not because of the high TSH, it's because of the complete lack of thyroid hormone. Conversely, if your TSH is unmeasurable, it means you have too much thyroid hormone, but the actual symptoms you have are from too much thyroid, not from too little TSH.

Among the body's major hormone systems—sex hormones, thyroid, adrenal, and insulin—the thyroid system is uniquely stable. Unlike insulin levels, which can change six-fold after a meal, thyroid hormone levels in the blood change very little. This stability once puzzled scientists. One perspective is that thyroid hormone is so critical it must be kept in a very narrow range, much like the body's pH.

The puzzle was solved with the discovery of enzymes called deiodinases. While thyroid hormone levels in the blood are stable, levels within specific tissues can change dramatically. Antonio explains this using an example from his research on brown fat, a tissue that generates heat.

If you expose a mouse or a rat to the cold, in a few hours, the T3 levels increase by tenfold. Not in the circulation, though. In the circulation, the levels are stable. If you're looking at the blood, nothing is happening. But in the tissue, T3 went up tenfold. And that's important for the energy activation in that tissue.

This local conversion of T4 to T3 allows the body to have precise, tissue-specific control, explaining how a stable hormone can have such dynamic effects.

An experiment with rats in a cold room revealed that within 24 hours, the amount of T3 in their brown fat skyrocketed tenfold, while T3 levels in the blood remained unchanged. This localized surge in T3 was shown to be critical for heat production. Antonio Bianco explains that a similar process occurs in the human brain. Most of the T3 in the brain is not sourced from the blood, but is produced locally from T4 by the enzyme type 2 deiodinase (D2).

This raises the question of how the hypothalamus senses thyroid hormone levels to regulate its own output. It turns out the hypothalamus responds to both local T3 production and peripheral hormones in the blood. This is possible because the part of the hypothalamus that regulates the endocrine system, the medial basal hypothalamus, is located outside the blood-brain barrier. This anatomical feature allows it to directly sense circulating hormones like T3, T4, insulin, estradiol, and testosterone.

The pvn, the paraventricular nucleus, where TRH is produced, is outside of the blood brain barrier. So T3 can get there from the blood. T4 can get there.

The hypothalamus and the pituitary gland both have high concentrations of D2. This is essential for the negative feedback loop. T4 from the blood is converted locally into T3 within these structures, which then signals to reduce the production of TRH and TSH. In this way, the system integrates signals from both circulating T3 and T4. The insights gained from studying brown fat were directly applicable to understanding T3's role in the brain, which has significant implications for patients with hypothyroidism.

To properly treat hypothyroidism, a deep understanding of thyroid physiology is essential. This knowledge helps distinguish between genuine therapies and ineffective or even harmful approaches. Antonio Bianco notes that many practitioners have an incomplete grasp of this physiology, which leads to confusion. A major point of contention is the measurement of T3, the biologically active thyroid hormone. Despite its importance, a strong school of thought argues against measuring it, which makes no sense from a physiological standpoint.

It's the biologically active hormone. And I attribute this to incomplete understanding of thyroid physiology. I've been studying the thyroid for about 40 years. It took me a while to understand, to put together important dots. It took me decades because I was listening through exactly those lines of thoughts. And then my patients started asking me, doctor, shouldn't we measure T3? Don't worry about it. This is so important and I lived through this.

When getting a blood test, it's important to understand the difference between total T3/T4 and free T3/T4. The vast majority of thyroid hormone in the blood, about 99.5%, is bound to proteins like thyroxine-binding globulin (TBG). This bound hormone is inactive because it's too large to enter the body's tissues. Only the tiny, unbound or 'free' fraction is biologically active and can get into cells.

Think of it like trying to go through a door while driving a car; it's impossible. You have to step out of the car (the binding protein) to walk through the door (enter the cell). Because the levels of these binding proteins can fluctuate due to factors like estrogen levels during pregnancy, measuring the total hormone level can be misleading. For this reason, doctors prefer to measure the free fraction (free T3 and free T4) alongside TSH, as this gives a more accurate picture of the hormone that is actually available for the body to use.

The standard lab tests for measuring T3 and free T3 are not very good. Unlike the test for free T4, which is considered a gold standard method, the assays for T3 have high variability. Antonio Bianco explains that these tests, known as immunoassays, are not reliable for T3. The best method for measuring T3 is mass spectrometry (mass spec), which provides a more accurate number for T3 in circulation. This is similar to how hormones like estrogen and testosterone are measured.

We never check estrogen testosterone on an immunoassay. We throw that assay in the garbage. And we specify LC-MS always. That's exactly what we need to do for T3.

However, a significant problem is that a CLIA-approved mass spec test for T3 is not widely available in major labs like LabCorp or Quest for routine clinical use. The host finds this disturbing, noting that immunoassay results for other hormones can be so inaccurate they are clinically useless. The issue with the T3 immunoassay lies in the quality of the antibodies used. While these assays have improved over time, they are far behind mass spec, especially at lower T3 levels where accuracy is most critical.

The test for reverse T3 is considered even worse than the one for T3. Antonio mentions an unpublished test where the same sample was measured using four different reverse T3 assays, and the results were completely different, essentially just noise. For consistency, it is best to use the same lab for repeated tests, as they will likely use the same assay. In summary, while TSH and free T4 tests are trustworthy, results for T3 and reverse T3 should be viewed with caution, particularly when the levels are low.

Genetics play a role in thyroid hormone levels, although it was previously thought not to be significant. Recent studies, particularly from the Netherlands, have shown there is some genetic influence. However, the clinical relevance of this is still a question. Doctors do not use genetic information to determine if a TSH level is normal; they rely on the standard range, which is quite broad, from about 0.4 to 4 or 5.

Genetics could potentially be helpful when treating a patient with hypothyroidism. The goal is to determine the ideal TSH level for that individual. Knowing a patient's historical TSH from before they developed the condition would provide the perfect target. This information might be available in old electronic medical records, but it is not common practice to use it. For now, the genetic influence is not considered significant enough to change clinical practice.

There are also minor differences between males and females. The TSH range in women is broader than in men. Males tend to maintain tighter control over their thyroid gland, while women show more variability in their thyroid function tests. But again, this difference is not believed to be clinically relevant.

Hypothyroidism is a much more common condition than hyperthyroidism. An estimated 20 million patients in the United States have hypothyroidism, which accounts for about 4% to 5% of the adult population. In contrast, hyperthyroidism is far rarer, affecting only thousands, or perhaps a few hundred thousand, people.

This disparity is evident in clinical practice. Antonio Bianco notes he might see 40 patients with hypothyroidism in the same month he sees only one or two with hyperthyroidism. While not a rare condition, hyperthyroidism is certainly less common.

Hyperthyroidism has two main causes, with one being an autoimmune condition called Graves' disease. In this disease, the body creates an antibody that mimics Thyroid-Stimulating Hormone (TSH). This antibody binds to the thyroid gland, tricking it into overproducing thyroid hormones T4 and T3. The entire gland grows and becomes hyperactive, leading to excessively high hormone levels in the circulation. Tissues are suddenly exposed to a two or three-fold increase in these hormones, which are normally very stable.

This overstimulation leads to several distinct symptoms. Antonio Bianco explains that heart palpitations are the most common complaint. Patients also experience weakness, jitteriness, agitation, and difficulty sleeping. They become easily triggered and have very rapid reflexes. Significant weight loss is also typical. A diagnosis can often be suspected just by shaking a patient's hand.

You're going to see that hand that's warm, very soft and wet because they're sweating, they're producing a lot of heat. Remember, thyroid hormone stimulates energy expenditure, so they're burning calories. You can just take their hand and you see that their uncontrolled hyperthyroidism is going on.

To confirm the diagnosis, blood tests are essential. They will show TSH levels near zero, as the brain tries to shut down thyroid stimulation. Levels of free T4 and T3 will be elevated, and testing for the specific antibody confirms Graves' disease.

There are three main treatment options. The first is medication, using anti-thyroid drugs that block the enzyme needed to produce the hormone. The second option is surgery to remove most or all of the thyroid. The third is radioactive iodine, which destroys the thyroid gland. Twenty years ago in the US, radioactive iodine was the primary treatment. In contrast, Europe favored medical treatment, where patients take drugs for one to three years hoping for remission, which happens in about 30-40% of cases.

Today, the approach has shifted. Radioactive iodine is now considered less safe due to studies linking it to an increased risk of other cancers. Antonio notes, "People are now moving away from giving radioactive iodine and they are going back to treatment with medicine." Surgery has also become a much more viable option because of highly specialized surgeons. The best surgeons perform 100 to 150 thyroidectomies a year, making the procedure safer and more reliable than in the past.

When treating Graves' disease, there are three main options that should be discussed with a patient, considering factors like age. One of these options is surgery. Typically, surgeons remove a standard amount of the thyroid to ensure a cure, rather than trying to calculate a specific volume to remove. While this aims to resolve the initial problem, it cannot guarantee the patient won't need thyroid replacement later. In fact, many will. Antonio Bianco explains that the autoimmune disease that stimulates the thyroid also has a destructive component. This means that even after successful treatment, a significant number of patients will develop hypothyroidism over the long term, perhaps ten years later. For individuals who had Graves' disease and were treated with radioactive iodine 20 years ago, Antonio advises they speak with their doctor about whether any additional cancer screening is necessary now.

Another form of hyperthyroidism is caused by hot nodules, which are growths or lumps in the thyroid. These can be a single nodule or a multinodular goiter that autonomously produces large amounts of thyroid hormone, essentially acting as a hyper-functioning adenoma. Historically, there have been three treatment options: medication, radioactive iodine, and surgery. Unlike autoimmune diseases, this condition will not go into remission on its own because it is caused by a physical growth that tends to get larger over time. While antithyroid drugs can be used to lower hormone levels, they are not a permanent solution. Radioactive iodine is also an effective treatment, with doses being empirical, typically between 8 and 10 millicuries. However, Antonio Bianco expresses a personal bias towards surgery. He believes that because modern surgical procedures are so effective, surgically removing the nodule should be strongly considered.

The way hypothyroidism is diagnosed has changed significantly over time. Decades ago, a diagnosis might start from a patient's symptoms. Now, it is almost always discovered through routine lab work. It is very rare to diagnose hypothyroidism based on symptoms alone because TSH is such a common screening test.

Today I cannot tell you the last time I made the diagnosis of hypothyroidism just because it's so easy. Everyone's showing up with labs. TSH is used as a routine test. It's so good, the test that you pick up everything. So even before it has clinical manifestations of hypothyroidism, you already have a TSH of 7 or 8 and you start to investigate.

The most common cause of hypothyroidism is Hashimoto's disease, an autoimmune condition. In this disease, the patient's immune system mistakenly attacks the thyroid gland, producing antibodies that target and destroy it. Over time, the thyroid can shrink and become atrophic, leading to a reduction in thyroid hormone production. The standard treatment is not to address the autoimmune attack itself, but simply to replace the missing hormone. Antonio Bianco explains the approach is to "let the thyroid die" and manage the condition with replacement therapy.

This treatment strategy assumes the autoimmune attack is confined only to the thyroid. However, that assumption is not entirely correct. Evidence suggests the autoimmune process can have broader effects. For example, a pregnant woman with a healthy thyroid might be found to have TPO antibodies, which are the markers for Hashimoto's. Even with normal thyroid function, the presence of these antibodies increases the risk of miscarriage and premature birth. This indicates the TPO antibody's presence is associated with something else, as the immune system attacking the thyroid may also be attacking other tissues, such as the fetus or placenta. Antonio notes that about 30% of people with positive TPO antibodies also have antibodies against brain tissue. This leads to the recommendation that pregnant women should be screened for TPO antibodies.

A connection can exist between different autoimmune diseases. For instance, infertility might be related to positive TPO antibodies. Antonio shares an anecdote about a patient who struggled to conceive and had high TPO antibodies, but was not hypothyroid. Her doctor treated her with prednisone to lower the antibodies, after which she became pregnant. While large-scale trial data is lacking, Antonio notes this is a common practice among infertility specialists.

This highlights the unique position of physicians who also conduct lab research, as patients can provide them with hypotheses. Antonio recalls a pivotal moment in his career when a patient, a teacher, told him she had to quit her job after becoming hypothyroid.

I'm a teacher. I lost my job because I became hypothyroid. I cannot teach anymore. I had brain fog. I became unfocused. I don't have that energy. I quit.

Initially, Antonio was skeptical because her TSH and free T4 levels were normal, and he suggested psychotherapy. However, two weeks later, another teacher presented with the exact same story. He realized it couldn't be a coincidence. Both women were high-functioning before their hypothyroidism, which was triggered by thyroid removal surgery in one case. The decline was immediate. This direct patient experience was so compelling that Antonio completely refocused his research to understand what was happening, despite it being a controversial area.

Hashimoto's is the most recognized form of autoimmune hypothyroidism, but other unnamed autoimmune conditions can also decrease thyroid function. An example is subacute thyroiditis, which involves severe, painful inflammation of the thyroid gland that can destroy it very rapidly. The pain can be so intense that a diagnosis is clear without even touching the patient's neck.

You're moving towards the patient. The patient is moving far away from you. Because the neck is so painful, you basically don't need to put your hands on the neck because you already know.

The reason Hashimoto's has a specific name is due to the identification of a particular antibody: the TPO antibody. There are two main antibodies checked for diagnosis, TPO and antithyroglobulin. Both are highly specific because they target proteins produced exclusively in the thyroid. However, the TPO antibody is considered the main and most important marker for diagnosis.

In conventional medicine, the standard of care for Hashimoto's disease does not typically focus on treating the underlying autoimmunity. Instead, the primary approach is to begin thyroid hormone replacement therapy.

However, some studies suggest that antioxidants like selenium and vitamin D can help. These supplements may reduce the levels of TPO antibodies and prolong the "honeymoon period," which is the time the thyroid continues to produce hormones despite being under attack. The rationale behind this is linked to the process of creating thyroid hormone. This process involves a powerful peroxidation reaction to bind iodine to the hormone, which is inherently stressful and potentially damaging to the thyroid gland. It generates free radicals as a byproduct.

Making the thyroid hormone is actually stressful. It could be damaging. When you give someone an antioxidant, you're actually slowing down that process or the free radicals that are produced as a byproduct of this reaction, and you tone down, you may decrease the autoimmunity process.

By using antioxidants, the oxidative stress and free radicals are reduced. This may tone down the autoimmune process by making the thyroid less of a target for the immune system. While some doctors incorporate this into their practice, it is not yet considered the standard of care.

The diagnosis for primary hypothyroidism requires a specific combination of biomarkers: a TSH level higher than 10 and a reduced level of free T4. Free T4 is a direct marker of thyroid function, as the thyroid's primary job is to produce T4. If free T4 is normal, the thyroid is still producing hormone, even if TSH is slightly elevated.

A patient with a positive TPO antibody and a TSH of 4, but a normal free T4, does not meet the diagnostic criteria. This scenario is considered a "honeymoon phase," and treatment is typically not initiated. However, clinical judgment is crucial and cannot be replaced by algorithms. Antonio Bianco emphasizes the importance of the doctor-patient relationship in making treatment decisions.

And that's why I'm sure AI is not going to replace us, because we need to talk to the patient. The doctor needs to have that relationship and say, how are you feeling? Is there hypothyroidism in your family? Let's do a thyroid ultrasound.

Factors like a strong family history of hypothyroidism can influence the decision. For a patient with rising TSH and a family history, re-testing in three months is a common approach to confirm the trend before starting treatment. It is also common to see a high TSH with normal antibodies. About 40% of hypothyroidism patients do not have positive TPO antibodies. This can be due to surgical removal of the thyroid, radioactive iodine treatment, congenital hypothyroidism, or other forms of autoimmune thyroid disease for which the cause is not yet known.

When it comes to treating hypothyroidism, the standard of care is T4, also known as levothyroxine. While there is an FDA-approved molecule for T3, it was never considered the standard treatment. Antonio Bianco explains that T3 was approved first, back in 1952, and was primarily used diagnostically for thyroid cancer patients, not as a primary treatment for hypothyroidism. Today, no guidelines recommend using T3 as a standalone therapy.

Despite this, a small number of patients do use T3 monotherapy. Antonio notes he has seen maybe 10 or 20 patients over the years who insist on it. He shares their perspective: "This is what I take. I take T3 and my body doesn't take T4, doesn't accept T4. And this is how I feel and please help me maintain this." While the reasons these patients feel this way are unknown, this approach is extremely rare.

A major challenge with T3 monotherapy is its short half-life. This causes a significant burst of energy and other effects, both positive and negative, after each dose. This makes dosing difficult, as one must chase the effects and avoid taking it too late in the day, which could disrupt sleep. In contrast, T4 has a very long half-life, making it a convenient, once-daily medication. Its stability in the body is a significant advantage. If a dose is missed, a patient can simply take two pills the next day, making it a very forgiving drug to manage.

Desiccated thyroid extract is a powder made from a pig's thyroid and has been used to treat hypothyroidism for about 125 years. It was the second treatment developed, following an initial attempt at transplanting a pig's thyroid into a woman in 1890. While the transplant worked for a few months, doctors soon realized they could simply dry the thyroid, make a powder, and have patients ingest it.

Interestingly, desiccated thyroid extract is not technically FDA-approved for treating hypothyroidism, though it is under the FDA's control. According to Antonio Bianco, this is because the drug existed before the FDA was created and was therefore grandfathered in. Today, a new drug could not come to market this way.

The fundamental difference between desiccated thyroid and levothyroxine (T4) is its composition. Desiccated thyroid contains both T4 and T3, while levothyroxine is only the prohormone T4, which the body must convert into the active T3. This difference is at the heart of a significant debate. The case for using desiccated thyroid is logical: a normal thyroid produces about 80% T4 and 20% T3, so replacing its function with a combination of both hormones makes sense.

However, concerns have been raised. Since T3 has a short half-life, taking it in a single daily tablet causes a spike in circulation. Doctors worried this could be dangerous, potentially causing hyperthyroidism symptoms like tachycardia and harming the heart, brain, or bones. Antonio notes this concern is completely unfounded, with no evidence to support it. Another historical problem was potency inconsistency, as different manufacturers used different standards. This was resolved in 1985 when a standardized method for measuring T3 and T4 content was established, ensuring a consistent 4-to-1 ratio of T4 to T3. Today, studies show its safety is identical to levothyroxine. Furthermore, in blinded studies, patients tend to prefer combination therapy, and two studies specifically show a preference for desiccated thyroid extract over levothyroxine alone.

Levothyroxine is the standard treatment for hypothyroidism. The rationale is simple: give the prohormone and let the body's deiodinases convert it to the active hormone. For 80-90% of patients, this works. They take a single, synthesized tablet, their major symptoms resolve, and their TSH levels return to the normal range. From a practical perspective, it seems like the perfect treatment.

However, the FDA has never required a single clinical trial for levothyroxine; it was approved without them. While it normalizes TSH, its clinical efficacy on outcomes like mortality has not been prospectively studied. Retrospective data paints a concerning picture. Antonio Bianco points out that mortality is 2.5 times greater in patients with hypothyroidism taking levothyroxine compared to a control population.

The question is whether this increased mortality is caused by the treatment or by the underlying condition and its associated comorbidities. Antonio argues that while comorbidities like other autoimmune diseases are a factor, levothyroxine provides an incomplete restoration of a euthyroid state. A key piece of evidence is cholesterol levels. Hypothyroidism causes elevated cholesterol because the liver cannot clear LDL effectively. When patients are treated with levothyroxine, their cholesterol often does not return to normal, even when their TSH does. Consequently, the number one co-medication prescribed with levothyroxine is a statin.

This tells you that the liver remains hypothyroid in a rat with normal TSH treated with levothyroxine... patient comes, oh, your cholesterol is slightly elevated. I'll give you statin number one, co-medication with levothyroxine. But that tells me the liver has a problem. The metabolism has not returned to normal.

This suggests that normalizing TSH in the blood does not guarantee that every tissue, like the liver, has returned to a normal thyroid state. To confirm this, a recent study compared 1.1 million patients on levothyroxine to healthy controls over 20 years. The study also compared about 90,000 patients on levothyroxine alone to 90,000 on combination therapy (T4 and T3). The results showed a 30% reduction in mortality for those taking combination therapy relative to those on levothyroxine alone. While mortality was still elevated compared to healthy controls, this finding confirms that adding a small amount of T3 provides a significant benefit.

A study showing a 30% relative risk reduction in mortality for hypothyroidism patients on dual T3/T4 therapy raises questions about confounding factors. It's possible that patients who seek dual therapy are more health-conscious or have more creative physicians providing better care, and that these factors, not the T3 itself, are driving the improved outcomes.

To address this, Antonio Bianco explains his research team controlled for these variables as much as possible. They found that hospital admission rates prior to the hypothyroidism diagnosis were similar between the dual-therapy and mono-therapy groups. They also used propensity score matching to control for comorbidities, BMI, sex, and age. At the outset, the two populations appeared very similar. However, he concedes they could not control for the physician's mindset, so that remains a potential factor.

Given the large mortality difference, it is surprising the FDA has not pushed for a prospective clinical trial, which could provide a definitive answer within four or five years. Antonio emphasizes the seriousness of the condition.

Hypothyroidism is not that naive disease that we thought it was. It's a deadly disease. It can affect significantly the quality of life of patients.

Patients with hypothyroidism have higher rates of dementia and other complications. He argues that physicians should view hypothyroidism as a serious complicating factor in a patient's overall health and give it extra attention.

A common perspective, particularly in functional medicine, suggests that many people have hypothyroidism despite normal lab tests. However, the diagnostic process relies on specific biochemical markers. Antonio Bianco explains that when assessing thyroid function for a diagnosis, TSH and free T4 are the essential measurements. T3 levels are not useful for diagnosis because the body prioritizes keeping T3 normal, even when the thyroid is failing. In early hypothyroidism, TSH will rise and free T4 will fall, but T3 will remain stable.

Patients often present with classic symptoms of hypothyroidism like fatigue, weight gain, hair loss, and low body temperature, yet have normal TSH and free T4 levels. Some may believe they have a rare condition called secondary hypothyroidism, where the pituitary gland fails to produce TSH. However, a key detail is often missed. Antonio clarifies the defining characteristic of any form of hypothyroidism, including secondary cases.

The important thing is the free T4 in these patients must be below normal because otherwise you don't have hypothyroidism. To have secondary hypothyroidism, you need to have hypothyroidism, which is the hallmark of hypothyroidism is a free T4 that's below normal with a TSH that doesn't go up.

If a person's free T4 is normal, their thyroid is functioning properly from a production standpoint. The symptoms, while real, are not specific to hypothyroidism. They can be caused by many other conditions, such as anemia, iron deficiency, or obesity. The number one confounding factor is menopause, as its symptoms are almost indistinguishable from those of hypothyroidism. Ultimately, despite patient frustration, clinical indicators like symptoms or body temperature are not reliable for diagnosis when compared to TSH and free T4 levels. Studies have confirmed that it's impossible to accurately diagnose hypothyroidism based on symptoms alone.

A low morning body temperature is often associated with hypothyroidism. While it's true that hypothyroidism will likely cause a depressed morning temperature, the causality only runs in one direction. A low body temperature does not necessarily mean you have low thyroid function.

Similarly, symptoms alone are insufficient for a diagnosis. Many confounding factors can present with symptoms that mimic hypothyroidism. Blinded analyses have shown that relying on symptoms is not enough, which is why biochemical markers are essential. This is quite different from androgen therapy, where treatment decisions can be heavily influenced by a patient's symptoms, even with borderline hormone levels. In that field, if a patient has complaints and feels better after treatment, it's often considered a success.

For thyroid conditions, however, the diagnosis must be anchored by blood tests. Specifically, a low free T4 level, along with TSH, is a critical part of the diagnosis. The presence of antibodies is not required for a diagnosis. Antibodies simply indicate that the underlying cause is likely an autoimmune process.

Compounded controlled-release T3 is a therapeutic option for hypothyroidism, but it comes with significant concerns. Antonio Bianco notes there is no scientific basis for its controlled-release claims. In fact, he is not aware of any published paper demonstrating that a compounded product has a true slow-release profile. One study that did test a company's claim found its product was identical to normal, immediate-release T3.

There's not a single paper in which a compounded product that was made in a pharmacy exhibited slow release profile.

Even reputable compounding pharmacies face challenges with accuracy. Measuring tiny amounts like 5 micrograms of T3 is very difficult. They must dilute the T3 by mixing it with other substances, like glycerol, and then assume the mixture is homogeneous. This process introduces variability. Given the controversies surrounding even FDA-regulated desiccated thyroid extract, compounded medications face an even higher level of scrutiny, yet the supporting data is often absent.

Antonio's preferred treatment approach begins with T4 (levothyroxine) for most patients. He stresses that hypothyroidism should be considered a risk factor for cardiometabolic disease, meaning patients require more intense monitoring of cholesterol and signs of cardiovascular issues. For patients who do not feel well on T4 alone, the first step is to eliminate other potential causes, such as menopause. If symptoms persist, combination therapy is the next step.

Synthetic combination therapy (T4 and T3) offers the flexibility to change the ratio of the hormones. Interestingly, research from 1965 found that the most effective T4 to T3 ratio was about 3.5 to 1. This happens to be the same ratio found naturally in desiccated thyroid extract from pigs. This makes desiccated thyroid extract a viable option, and about 1.5 million patients in the US currently use it. A key advantage of using a brand-name desiccated product over a compounded one is that it is under the constant surveillance of the FDA. Patients can check the FDA website for recalls on all thyroid medications, including desiccated thyroid extract and generic levothyroxine.

When comparing branded Synthroid (made by Abbvie) to generic levothyroxine, studies consistently show there is no difference in their effectiveness. Antonio Bianco explains that the perception of the branded drug being superior stemmed from marketing pressure by manufacturers. This idea became so ingrained that a 2012 American Thyroid Association guideline even recommended using branded levothyroxine, despite having no evidence to support that position.

While there can be concerns about the quality of generic drugs in general, levothyroxine is under very strict FDA control. The potency requirement is that the dosage must be within plus or minus 5% of the stated amount throughout the medicine's shelf life. This tight regulation is crucial because even small variations can have significant biological effects.

The primary goal of thyroid therapy, according to professional society guidelines, is to normalize the patient's TSH level. This is referred to as achieving 'biochemical euthyroidism'. However, this approach often overlooks the patient's actual symptoms.

The goal of the therapy is to achieve biochemical euthyroidism, is not to achieve clinical euthyroidism. And why do we say that? Because we know we cannot achieve clinical euthyroidism in all patients. To make it easier for the doctor, to provide some rationale for the doctor, just normalize TSH. But I argue that if the patient continues to exhibit symptoms, we did not achieve an ideal therapy.

Antonio argues that if a patient continues to exhibit symptoms, the therapy is not ideal. The medical community is slowly shifting its perspective. It is moving away from the old view of sending symptomatic patients to psychotherapy and toward recognizing that levothyroxine is an incomplete treatment for some. For these individuals, combination therapy, using either synthetic options or desiccated thyroid extract, might be considered.

A clinical case study illustrates a scenario where a patient's free T4 is corrected and symptoms are fine, but their TSH remains significantly elevated. The patient, a healthy man in his early 50s, initially presented with a TSH of 74.7 and a low-normal free T4. After starting T4 treatment, his TSH dropped to 23.7 within six months, but he began complaining of hyperthyroidism symptoms.

For four years, various treatments were attempted, including desiccated thyroid and combination synthetics. However, they could not normalize his TSH without him experiencing subjective signs of hyperthyroidism. This raises the question of whether to accept an elevated TSH as long as his symptoms and free T4 are within a reasonable range.

Antonio Bianco suggests several diagnostic possibilities. Since the patient had a normal TSH in the past, a congenital genetic issue is unlikely. His first hypothesis is an interference in the lab assay. Humans can develop antibodies against rodent proteins from environmental exposure. Because the antibodies used in TSH assays are often made in rodents, this can lead to inaccurate results. While it's unusual for the TSH to decrease so much if there's interference, a change in labs could explain it. A specific test can check for these interfering antibodies.

Other, less likely possibilities include a non-cancerous pituitary tumor (unlikely without hyperthyroid symptoms), or aggregated TSH molecules confounding the assay. In some rare cases of long-term hypothyroidism, the TSH can be difficult to normalize, but not usually to such high levels. Given the circumstances, Antonio concludes it would be reasonable to monitor the patient's free T4 levels and disregard the TSH value.

Antonio discusses a clinical case of a 58-year-old woman with a very sensitive pituitary response to T4 monotherapy. Even a small change in her dosage, like from 100 to 112 micrograms, causes her TSH to swing dramatically from extremely low (0.06) to very high. This makes it difficult to manage her treatment based on TSH levels alone. To feel well, she requires a dose that suppresses her TSH to nearly zero.

While there is no clear molecular explanation for why some individuals have such a nonlinear and sensitive TSH response to T4, the clinical approach is straightforward. In these situations, the TSH is no longer a trustworthy marker. Instead, the focus should shift to monitoring the free T4 level and keeping it within the normal range. Antonio explains that if the free T4 or free T3 levels are abnormal, something is wrong with the treatment.

This principle is also applied in other contexts, such as treating a pregnant woman with hyperthyroidism. To protect the fetus from hypothyroidism, clinicians administer the lowest possible dose of antithyroid medication. They accept a suppressed TSH and instead aim to keep the mother's free T4 in the upper limit of the normal range. In rare cases where TSH is unreliable, clinical judgment and other lab values like free T4 become the most important guides.

Some people advocate for avoiding iodized table salt in favor of non-iodized versions, while also taking very high doses of iodine supplements. However, this practice carries significant risks, particularly for thyroid health. The recommended daily iodine intake is about 150 micrograms for adults and 250 micrograms for pregnant women. Consuming amounts well above this can be problematic.

A clear example comes from Japan, where the normal diet provides about 500 to 600 micrograms of iodine per day. This higher intake is associated with an increased incidence of autoimmune thyroid disease. Antonio Bianco explains that excess iodine can disrupt thyroid function.

The excess of iodine is going to mess up with the thyroid. It will cause increased antigenicity of the thyroid and trigger autoimmune disease.

This typically leads to autoimmune hypothyroidism. Additionally, high iodine intake can trigger hyperthyroidism in some individuals. If a person has a silent, non-functioning nodule in their thyroid, a sudden influx of iodine can provide the substrate for the nodule to become overactive, leading to iodine-induced hyperthyroidism.

Hypothyroidism is about 10 times more common in women than in men, a significant difference for which there is no clear explanation. While a condition called postpartum thyroiditis exists, where hypothyroidism develops after childbirth, pregnancy doesn't account for the overall disparity. One theory suggests the female thyroid might leak more antigens due to sex hormones, making it more prone to an autoimmune response, but this is not confirmed.

A common clinical scenario is subclinical hypothyroidism, where a patient has an elevated TSH level (e.g., 8 or 9) but normal free T4 levels and no symptoms. For a 40-year-old, this TSH level is not considered normal. The first step is to investigate the cause, which involves checking family history and performing a thyroid ultrasound to look for signs of Hashimoto's disease. Even if there are no clear indicators of developing full-blown hypothyroidism, studies show that treatment with levothyroxine can offer metabolic benefits, such as improving cholesterol levels. Therefore, treatment is often favored.

However, age is a critical factor in interpreting TSH levels. TSH naturally increases as people get older. This is a crucial detail that is often overlooked.

After 50 years of age, your TSH will increase by 1 point. Your upper limit of normal will increase by 1 point every 10 years. So for someone that is 80 years old, it's okay to have the upper limit of normal, 8. For 90 years old, it's okay to have a 9.

This means a 70-year-old with a TSH of 6 is considered perfectly normal and should not be treated with levothyroxine based on that number alone. The diagnostic range for TSH must be adjusted for age.

The biggest blind spot in thyroid care today is the treatment of hypothyroidism. With 20 million patients in the U.S., many of whom suffer despite treatment, the field needs to move beyond simply normalizing TSH levels. According to Antonio Bianco, two key areas need significant improvement in the next decade.

First, there is a need for better methods of measuring T3. Antonio states that mass spectrometry for T3 is mandatory to get a reliable and robust measurement, with the goal of normalizing T3 in the circulation for patients with hypothyroidism. Second, the pharmaceutical industry must develop a slow-release T3 medication. While studies show that even short-lived T3 is beneficial compared to levothyroxine alone, a slow-release version would provide more confidence for physicians.

Having the slow release T3 will give that confidence to the physician that they're not doing any harm. You're just doing what the thyroid does. That's what we need.

Two approaches for slow-release T3 are currently in development. One, being pursued in the U.S., involves a polymer of T3 that slowly breaks down in the intestine. It has successfully completed a phase one trial. Another approach from a group in Italy uses sulfate T3. This inactive compound is absorbed and then steadily converted into active T3 by the liver, which acts as a constant source. The hope is that these new treatments and better lab tests will become available for patients within the next 10 years.