Hello, hello, and welcome to today's podcast. Today we're going to be talking about the thyroid. We recently did a series on hormone systems, and thyroid got a lot of attention.
The thyroid may be a small gland, but it's a mighty gland — it affects everything in our system. There's a lot of controversy and misunderstanding about how it works, how to treat it, and what to do with it, so we'll try to clear some of that up. This isn't all-inclusive; we're just trying to create awareness and educate folks about what it really does.
When "Normal" Labs Don't Tell the Story
Thyroid symptoms are one of those things where your labs can look normal, because typically the labs tested are a TSH and a free T4 — and those can look normal even when other parts of thyroid function don't. So it's one of those things that can look normal while you're still feeling not normal. TSH plays a big part in how people get treated; insurance requires an abnormal TSH before they'll cover medication for hypothyroidism, which is why TSH is such a big one. Because these labs don't always correlate, a lot of things go undiagnosed or misdiagnosed.
We're talking about something that weighs half an ounce. This tiny, double-lobed gland sits at the lower base of the neck, with one lobe on each side connected by a little bridge called the isthmus. Its dysfunction affects everything — midlife energy, weight, mood, metabolism, and even our hormones. But it doesn't work alone; it's part of a larger hormonal orchestra, interconnected with the other hormones in our system. So many of these systems are connected — the whole person is one big picture that needs to be looked at together.
The Metabolic Thermostat
To put it simply, your thyroid is like a metabolic thermostat, telling your HVAC system — your body and cells — how hot or cold they need to be. It touches energy production, body temperature, heart rate, digestion, brain function (including mental health), cholesterol and lipids, and menstrual cycles and fertility. It's incredible — it touches everything.
Hypothyroidism vs. Low Function
Let's talk about the most common condition people think of: hypothyroidism, or low thyroid function. There's a difference between low function and clinical hypothyroidism. A person can have normal lab values but be non-optimal, and low function is why you may feel cold, tired, and fatigued. Hypothyroidism is more of an insurance ICD-10 diagnosis that requires a high TSH level.
Backing up a step: TSH is a hormone secreted from the brain that signals the thyroid to produce hormone, and then a cascade of events makes the thyroid hormone into its active form. That's how we diagnose hypothyroidism. Symptoms that show up even before you're clinically hypothyroid include fatigue, weight gain, cold intolerance, constipation, hair thinning, depression, brain fog, and dry skin. A lot of people in midlife and beyond — as well as younger individuals — have trouble with those things, and yes, it can be the thyroid, though there are many other possible causes too.
Thyroid Hormone Resistance and What Affects It
Just like there's insulin resistance, there's thyroid hormone resistance, where the hormone may be in the normal range in your bloodwork but the cells aren't responding to it. There are a lot of reasons cells don't respond — blocked receptors, receptor density — and these can be affected by inflammation (including insulin resistance, which is a significant form of inflammation), stress, and nutrient deficiencies. A lot of people are familiar with iodine, selenium, and zinc as nutrients that affect the thyroid, but iron and vitamin D directly affect thyroid production too. And environmental toxins, just like they affect everything else, can affect how the thyroid functions.
Hashimoto's Thyroiditis
The next thing people are familiar with is Hashimoto's thyroiditis, an autoimmune condition where your body attacks your thyroid. Essentially, Hashimoto's is a form of hypothyroidism — a low-functioning thyroid that ensues. The biomarkers to identify it are the thyroid antibodies: TPO (thyroid peroxidase antibodies) and TG. Your system develops these antibodies to destroy its own thyroid, affecting the thyroid peroxidase protein. TPO is very important for creating thyroid hormone, so if we're deficient in iron or have immune issues leading to autoimmunity, we don't make thyroid hormone.
One thing frequently looked at with Hashimoto's is gluten. Gluten can be very inflammatory, and very often someone with Hashimoto's who removes gluten sees those inflammatory numbers come down and get into better control. Over 70% of your immune system — the gut-associated lymphoid tissue — is located in your gut, so when you throw in something that creates such an inflammatory response, your body reacts, which can exaggerate the immune system and trigger antibody production.
Hashimoto's is the most common cause of hypothyroidism in the United States, hands down. You can have Hashimoto's without a technically low thyroid, but it's something to be aware of and watch. If a patient with Hashimoto's is only having TSH and T4 tested, they're missing the TPO — watching how TPO fluctuates gives great feedback about whether your lifestyle is helping or hurting.
Over 5% of the population has Hashimoto's, and many aren't diagnosed because they're not getting antibody levels checked — providers go off TSH or T4. You can have normal TSH and normal thyroid hormone levels while having significantly elevated antibodies, and if you don't check them, you won't realize your thyroid will eventually burn out and stop producing hormone. Caught early, you might reverse some of it. Women are seven to ten times more likely than men to have Hashimoto's — whether that's hormonal, or partly because more women go down the path to get tested while men often don't.
Why Thyroid Dysfunction Matters
An estimated 20 million Americans have thyroid disease, and the majority don't realize it. Thyroid dysfunction is important because it increases your risk for cardiovascular disease, depression, infertility, cognitive decline, and metabolic syndrome. If you don't catch it, you run higher risks of these chronic diseases, which is why proactive steps to identify it matter — once disease progresses, it's harder to reverse.
The thyroid is connected to everything, including estrogen, testosterone, and progesterone, which all influence each other. Progesterone supports thyroid signaling, and estrogen affects the thyroid binding proteins, so these other hormones can directly affect the thyroid at the cellular level.
Thyroid and Metabolism
This is where it gets a little confusing because we talk about TSH so much. When TSH is high, that's when the active forms of thyroid are clinically low — because your brain (the hypothalamus and pituitary) is trying to signal the thyroid and has to "turn up the volume" for the thyroid to hear it, because it's not producing enough. Your radio's on, but the volume isn't turned up.
Weight is very frequently associated with thyroid — so many people (myself included) want their thyroid checked because what they used to do isn't working the same. A change in body composition gets you to the doctor, they check your TSH, it's normal, and that's the end of the story. But chronic constipation and depression can also be related to low-functioning thyroid. Lower thyroid function equates to a slower metabolism — everything slows down. It even affects your lipids and insulin sensitivity; you can have elevated lipids because of low thyroid function.
Thyroid, Brain, and Mood
Low thyroid affects your brain and mood — depression, anxiety, brain fog, and low motivation. This is another place where antidepressants come in to offset an unknown cause, because your provider drew TSH and T4, they look normal, and the conclusion is "it's not your thyroid, you're just depressed, maybe you need an antidepressant." But there are other options — if we can optimize the thyroid, that may help improve or even resolve the depression and anxiety.
Thyroid and the Gut
The thyroid and gut are connected through autoimmunity. If there are issues with permeability in the intestinal tract, that sets you up for more invasion, a more inflammatory response, and autoimmunity. Then you have trouble with nutrient absorption. Low iron is an issue because thyroid peroxidase needs iron to add iodine back onto the thyroid molecule — which is why people who choose not to eat meat sometimes have to support their iron. Even vitamin D directly influences autoimmune diseases like Hashimoto's, and vitamin D is very commonly low or deficient. We have patients who are outside for their job all day, all year, and still have a vitamin D deficiency. In general, the only patients who walk in with optimal vitamin D are the ones already supplementing it.
What to Test
Good foundational thyroid biomarkers are TSH, free T4, and free T3, plus the TPO and thyroglobulin antibodies — it's imperative to get those. Reverse T3 is an inactive form affected by stress that gives you input about how much stress you have; if you can't tolerate stress or have too much, you'll have more reverse T3. We also look at iron and ferritin on everybody, vitamin D on everyone, and several inflammatory markers. If thyroid is an issue, you can dig deeper into selenium and iodine — the body tightly regulates iodine, and selenium comes from few sources (Brazil nuts are great — one or two a day is more than adequate). The body doesn't need much selenium, but it needs it to make thyroid hormone.
It's important to understand that TSH is just what your brain perceives of the thyroid hormone level in your bloodwork. It doesn't say anything about how well your cells are seeing the thyroid hormone or whether there's a problem at the receptor sites. That's why people can have normal labs and still feel cold, tired, depressed, and fatigued. And TSH looks at the T4 level — you can have a normal free T4 but not a normal or optimal free T3, which is the actual active part. Your thyroid produces a hormone that isn't active; it has to be converted to the active form, which is fascinating.
Types of Thyroid Replacement
The two main forms of thyroid replacement can be thought of as synthetic and natural. If someone has a hypothyroid diagnosis, they're typically treated with synthetic T4 — levothyroxine (Synthroid). There's also synthetic T3 — liothyronine (Cytomel). The natural, bioidentical form is desiccated thyroid, derived from pig thyroid, and importantly it contains a mixed component of both T4 and T3.
Sometimes people don't make the conversion from T4 to T3, and T3 is the active part that creates the expression in the cells. Every cell in your body has thyroid receptors — even the placenta has them during pregnancy. Patients often just feel better when given the active T3 component, which makes them more energetic and improves their symptoms. But it requires careful dosing. When we have a patient on thyroid replacement, I want to see their TSH go down — below normal — which tells me there's an adequate amount of thyroid telling the brain to calm down and stop stimulating the thyroid. That's typically where we start to see symptom improvement.
This is where symptoms really help guide treatment. If your symptoms are improved, that's where we need to be — even if your T3 isn't at the level some people need to feel optimal. Too often providers look only at lab values and say, "You look good, you're in the normal range," but that doesn't mean the cells are receiving the signal.
Desiccated thyroid has been around a really long time — so long it's often dosed in grains, which nothing else is. There isn't one "best" replacement; everybody is different, receptors and receptor densities differ, and circumstances differ. We're all snowflakes. Normal is not optimal — just because you have normal lab values doesn't mean that's where you need to be, and optimal is different for every person. Symptoms make the difference: you have to treat the person based on their symptoms, not always their lab values, because overtreating and undertreating can both cause harm. Stay in contact with your provider about how you're feeling. As Peter Attia talks about, longevity depends on your metabolic and hormone alignment.
Takeaways
We covered a lot, but the key is that normal is not optimal, everyone's different, and you have to base treatment on symptoms and advocate for yourself. Keep asking — digging deeper can be the answer, and even when it isn't, it lets you rule something out and move on. Thyroid health also requires the proper medication, nutrient replenishment, stress management, and lifestyle changes to support healthy function.
Hopefully that cleared up a little of the muddiness. Not everything is related to your thyroid — just because you're tired with low motivation doesn't mean your thyroid is the problem — but there are a lot of symptoms that relate to low thyroid function, and the point isn't necessarily to diagnose someone with hypothyroidism before replenishing their thyroid. Let us know if we missed anything, and if you have any questions, send them our way. We look forward to seeing you next time. Have a healthy day.