In my last post, I explained that TSH or Thyroid Stimulating Hormone is produced by the pituitary gland and its job is to tell the thyroid gland to pump out thyroid hormone – T4 (along with a little T3 but mostly T4).

T4 (thyroxine) is the inactive form of thyroid hormone. When the body is nourished and balanced T4 is primarily converted to T3 (triiodothyronine), the active form of thyroid hormone. Yay, all is right in the body! The next step is T3 easily makes it way into the cells and the body produces all the energy it needs to function optimally – basically you feel great. That seems simple enough. Not to be a total downer but it’s a little too simple. There is also something called reverse T3 (rT3), also converted from T4.

Back to T3. When T4 is converted to T3 it’s “activated”, it’s about four times more potent than T4. This is good, activated T3 is revved up, ready to get the body moving, turn on the metabolic system and generate energy. SWEET! Activation, energy, cool but you know what’s also very cool, the constant dance the body does to maintain homeostasis – balance. If something is being “activated” you can bet that our finally tuned body has some counter measure in place. That would be reverse T3. rT3 has zero potency. It’s basically a place holder and it blocks activated T3 from getting into the cells. You can read more about “activation”, homeostasis and the molecular differences between T3 and rT3 here.

Every cell in the body has receptor sites, little doors that nutrients go through. The little door that lets T3 into the cell can get blocked by rT3. Once that happens no T3 gets into the cell, no T3, no energy production.

I know what you’re thinking, I HATE rT3! Hate is a strong word but I’m with ya. Before we expend too much of the energy we do have hating on rT3 I’ll try to explain why we need it. Yup, we actually need it – homeostatic balance.

Normally the seesaw ratio of T3 to rT3 is heavy on the T3 side but this ratio shifts when the body is under attack. The body needs time to figure out how to address a “threat” so it wants to stores energy while it works out a response. This is typically a short-term thing. During this time, also known as a period of metabolic slowdown the ratio of T3/rT3 switches to more rT3. Kinda cool, right? T4 is still being pumped out by the thyroid gland and it has to be used in someway so it gets converted to rT3 – don’t want more T3 because the body is trying to put on the brakes.

If, by chance have lab results for total or free T3 and reverse T3 and want to know what your ratio is, here is a link to a calculator. It’s important to make sure both values have the same unit of measurement. The calculator gives you options so you get the correct ratio.

O.k. so, I think we all understand the relationship between T4, T3 and rT3. It’s important and under the right conditions magical. Thyroid function, on the cellular level is down-regulated, meaning energy production is down-regulated when the body needs to address an acute (short-term) threat. In this modern-day that threat could come in the form of injury, stress, infection, inflammation, starvation (think diet), poison, food intolerance, stuff like that.

Are you thinking – “what do you mean, short-term!?” That’s what I thought when I first looked at that list. O.k., injury might be short-term, food poisoning might be short-term but stress, inflammation, food intolerance more long-term or chronic, wouldn’t you agree?

Long-term or chronic, there lies the problem. Modern day chronic problems: inflammation from autoimmune conditions, chronic low-calorie dieting, chronic viral infections, systemic inflammation from unaddressed food intolerance, and everyone’s favorite, chronic stress. All of that (and more) keeps the T3/rT3 ratio heavy on the rT3 side. Not good. This is known as functional hypothyroidism at the cellular level.

Here’s a nice blurb about rT3 by Dr. Kent Holtorf, MD that I found over at Mary Shomon’s blog.

Reverse T3 is actually an “antithyroid” — T3 is the active thyroid that goes to the cells and stimulates energy and metabolism. Reverse T3 is a mirror image — it actually goes to the receptors, sticks there, and nothing happens. So it blocks the thyroid effect. Reverse T3 is kind of a hibernation hormone, in times of stress and chronic illness, it lowers your metabolism. So many people seemingly have normal thyroid levels, but if they have high Reverse T3, they’re actually suffering from hypothyroidism.

I’m happy to be passing this information about the thyroid along. The tricky part to this is finding a doctor that understands all of this. As I think I mentioned in my first post, if your TSH looks good (and their idea of good may be way off) most doctors won’t do further testing.

Here are some doctor search links that might help you find a functional medicine doctor willing to look a bit deeper.

My next thyroid post will be about natural ways to support thyroid function.

Eat well, have fun, feel great!


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