A plea to our scientists, for an investigation of the Low T3 Syndrome

First, a caveat

This is a (very lightly paraphrased) account of my discussion of Heart failure and the Low T3 Syndrome, with Microsoft’s “Copilot”. It is a long, word-for-word printout, intended (hopefully) to stimulate some scientific person to mount a purposeful investigation into the Low T3 Syndrome: its impportance, diagnosis and management.
IF YOU ARE INTERESTED, IT WILL BE A GOOD “READ” FOR YOU. IF YOU ARE NOT, DON’T BOTHER.

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May 8th, 2026

A few days ago my newsfeed delivered an interesting paper on Heart Failure, titled “Data shows Heart Failure rising among younger Canadians, A cardiologist explains why”. Written by By Aarjavee Raaj and published on May 05, 2026. it is available at https://www.ctvnews.ca/health/article/heart-failure-rising-among-younger-canadians-data-shows-this-cardiologist-explains-why/.
The paper is interesting to me, not only for its shocking content, but because of what it doesn’t say.

Anyway, the message is important in the context of Canadian public health and our health-care system, so for your interest, I have paraphrased, abridged and italicised it: see below……

The paper

According to the Canadian Heart Failure Society, the Canadian Cardiovascular Society and the Canadian Journal of Cardiology, over the past few decades there has been an increase in cases of heart failure and heart-related diseases in young Canadians. Heart failure is now manifesting at earlier ages and hospitalizations for “HF” rose significantly among adults aged 20 to 39, between 2007 and 2016.

According to “Heart & Stroke”, data from the Canadian Chronic Disease Surveillance System, an up-to-date analysis showed that more than 5,000 Canadians between the ages of 40 and 49 were newly diagnosed with heart failure in 2023-24

Dr. Margot Davis, president of the Canadian Heart Failure Society, in discussing the problem, said (parphrased): “Remarkably, in the recent decade or two, we’ve seen that the proportion of older patients diagnosed with, and dying of, heart failure remains relatively static: they might even be improving a bit as we get better at treating it – but at the same time, we’re seeing an increasing rate in younger patients, who now make up a greater proportion of our heart failure population.”

She explained that there is a “greater burden” of risk factors for heart failure among people in the younger demographic, leading to an earlier onset of Heart Failure – “There’s a lot of heart failure that’s caused by things like diabetes, high blood pressure, obesity and coronary artery disease – all of these things that used to be much more prevalent in older patients are increasingly common in younger patients as time goes on”……..

Dr. Davis explained that Heart Failure in young people is treated in the same manner as it would be if it were an older person. “But oftentimes, health-care providers aren’t thinking of heart failure when younger patients present with sym,ptoms, so they go undiagnosed until they have much more advanced disease. Then it’s much harder to treatso we have worse outcomes in those patients.”

How this paper misses the salient point

I began, first, with the premise that the “risk factors” mentioned by Dr Davis (diabetes, high blood pressure, obesity and coronary artery disease), are related to the low T3 Syndrome in a “back-and-forth cause-and-effect manner and that they, with or without other dieases and/or aberrations, cause the Low T3 syndrome and further, that T3 deficiency is the real cause of a cardiomyoplegia which precipitates HF. Secondly, I found that, as is usual with scientific reports, no mention was made of the Thyoid hormone and its relationship with cardiomyocyte function.

Then, it occurred to me that in writing about this article, I would be reiterating once again, my prepcupation with a favourite subject, the “Low T3 Syndrome” – and that my readers must be bored stiff, by my repetitiveness!

So I decided to discuss the subject with “Copilot”, Microsoft’s version of AI: the discussion, protracted due to Copilot’s verbosity, has been lightly paraphrased for brevity, but basically verbatim. It is recorded below the synthesised photo showing “us”, chatting over coffee:

G Harry: what is the metabolic mechanism by which heart failure comes about?

Copilot: Heart failure occurs when mitochondrial ATP generation cannot meet the energetic needs of contraction:

G Harry: It has been said that cardiomyocytes, though dependent on T3, are unable to produce it from T4, thus needing a supply of FT3 from the blood and that cardiomyoplegia, the bottom-line cause of “’heart failure” develops as a result of the Low T3 Syndrome. Could that be correct?

,.. IN ANSWERING THIS QUERY, PLEASE DO NOT TRY TO SAY WHAT I WANT TO HEAR !

Copilot: This is truth, even if it opposes the “T3 hypothesis” – Your claim has two parts:

1. Cardiomyocytes depend on T3 but cannot generate it from T4.

2. Therefore, Low T3 Syndrome → cardiomyoplegia → the true cause of heart failure (HF).

G Harry: Do cardiomyocytes depend on T3?

Copilot: YES, Unequivocally: A cardiomyocyte deprived of T3 becomes energetically inefficient, slower to relax, weaker in systole, more glycolytic and more prone to ROS and mitochondrial fragmentation. This is real biology, not speculation.

G Harry: Can cardiomyocytes convert T4 into T3?

Copilot: Here is where the story gets interesting: The heart does NOT express meaningful D1: it expresses only trace D2. AND it iegulates D3 in stress, ischemia, inflammation, and HF.

G Harry: Does LT3 Syndrome cause cardiomyoplegia?

Copilot: Low T3 Syndrome (LT3S, aka NTIS) is characterized by ↓ serum T3, ↑ rT3, normal or low-normal TSH, suppressed D1, suppressed D2 and upregulated D3. This pattern is not primary thyroid failure. It is a stress response, driven by cytokines, hypoxia, and mitochondrial dysfunction.
It produces:
1) ↓ SERCA2a, (SERCA2a, the Sarco/Endoplasmic Reticulum Ca² – is the cardio-specific calcium pump in the sarcoplasmic reticulum that drives myocardial relaxation by transporting Ca²⁺ from the cytosol back into the SR. It is essential for normal excitation–contraction coupling, and reduced SERCA2a activity is a hallmark of heart failure).
2)↓ mitochondrial ATP production, ↓ FAO, ↑ glycolysis, ↓ contractility, ↑ diastolic stiffness: This is cardiomyocyte metabolic depression. LT3S is not the primary cause of heart failure. It is a secondary amplifier, not the initiating lesion.

G Harry: Why do you say that Low T3 Syndrome isn’t a cause of HF?

Copilot: Heart failure begins with ischemic injury, pressure and volume overload, toxic injury or metabolic disease like diabetes, or obesity: Low T3 Syndrome appears after these processes begin: it worsens the situation, but does not initiate it: the evidence is that T3 levels fall after HF onset, not before. And T3 replacement improves hemodynamics, but does not reverse HF.
Thus, D3 upregulation in the failing heart is a response to stress, not a cause of it.
Also, animal models with induced Low T3 do not spontaneously develop HF unless another injury is present. So the causal arrow is Primary cardiac injury → mitochondrial dysfunction → D3 upregulation → Low T3 Syndrome → worsening contractility……. Not the reverse.

G Harry: I understand that logic, but Is “cardiomyoplegia” a real phenomenon?

Copilot: Yes. Low T3 produces a state of metabolic hibernation in cardiomyocytes, but this is adaptive in the short term and maladaptive when chronic.It is not the initiating cause of HF.

It is analogous to hibernating myocardium in ischemia, fetal gene reprogramming and metabolic downshifting in sepsis: The heart is trying to reduce ATP demand when supply is inadequate.

Having said that, the proposition that The heart depends on circulating T3 is true and in addition, the failing heart upregulates D3, destroying local T3. Systemic Low T3 Syndrome deprives the heart of T3, its essential metabolic hormone. This produces “cardiomyocyte hibernation”, which contributes significantly to HF progression.

However the statement “LT3S is the cause of heart failure” is not supported by temporal sequence, genetic models, clinical trials or pathologic evidence: Low T3 is a major amplifier, not the root cause.

In summary, you are right, that

• Cardiomyocytes need T3 and they can’t generate it from T4

• There is D3-driven T3 starvation in HF

• Metabolic depression of the myocardium results

• T3 therapy is reasonable, in selected patients

But the statement: “Low T3 Syndrome is the cause of heart failure” is not correct.

Heart failure is a primary mitochondrial and structural disease, with Low T3 Syndrome acting as a potent metabolic accelerator of decline, not the origin.

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G Harry: I do not dispute the fact that HF causes LT3S. However LT3S occurs with all severe and/or chronic disease………. Therefore my argument begins with the premise that the “risk factors” mentioned by Dr Davis, with or without other dieases and/or aberrations, cause the Low T3 syndrome and that T3 deficiency can be the cause of a cardiomyoplegia which precipitates HF..

Copilot: You’re doing what good clinicians do— trying to unify a messy cluster of “risk factors” into a mechanistic story that actually makes sense. Let’s stres-test your premise:

1) Your core claim (restated) is:

Chronic diseases and cardiometabolic risk factors (diabetes, HTN, obesity, CAD, etc.) → Low T3 Syndrome (LT3S) → T3-starvation cardiomyoplegia → HF. HF is therefore downstream of systemic T3 deficiency, not just a cause of LT3S.

2) I’ll admit that those risk factors do producce a low-T3 phenotype;

• Obesity, insulin resistance, and T2DM are associated with altered deiodinase activity, low-normal or low T3 and increased D3 expression in inflamed and hypoxic tissues.

• Chronic inflammation, oxidative stress, and cytokines (IL-6, TNF-α) suppress D1/D2 and induce D3, shifting T4 toward rT3 and away from T3. This is the backbone of NTIS/LT3S.

• CAD and chronic ischemia upregulate D3 in myocardium and reduce local T3 signaling, even with “normal” serum thyroid tests.

  So your assumption that risk factors → LT3S is biologically plausible and partially supported. But it’s incomplete and not universal: many obese/diabetic/hypertensive patients have normal or even high-normal T3.

• LT3S is most consistent in advanced or decompensated disease –it is more tightly linked to disease severity and stress than to the mere presence of risk factor, not early risk-factor stages.

G Harry: Does T3 deficiency create a cardiomyoplegia phenotype?

Copilot: Low T3 (systemic or local) in the heart leads to:

• ↓ SERCA2a, ↑ diastolic stiffness

• A shift to β-MHC, slower cross-bridge cycling, ↓ contractile velocity

• ↓ mitochondrial biogenesis and FAO, ↑ glycolysis, ↓ ATP reserve

• ↓ β-adrenergic responsiveness

That is a T3-dependent cardiomyoplegia / metabolic hibernation phenotype.

From animal and human data: Hypothyroid or T3-depleted models show reduced LV contractility, prolonged relaxation, and impaired exercise tolerance, reversible with T3.

• In HF patients, lower T3 correlates with worse EF, higher BNP, and higher mortality, independent of traditional risk factors.

So: T3 deficiency is not just an epiphenomenon; it has real, directional, depressant effects on myocardial performance.

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G Harry: You said “T3 or thyroid hormone analog therapy in HF improves hemodynamics and some remodeling indices, but does not “cure” HF and has not shown robust, definitive mortality reversal in large trials.” BUT there are no large trials, because thyroid function is ignored in the majority of papers!

Copilot: You’re right to call that out—and you’re right on the facts.
When I said “has not shown robust, definitive mortality reversal in large trials,” the more precise statement is, “There are no large, adequately powered RCTs of T3
(or T3-centric strategies) in HF, because thyroid status is usually treated as background noise, not as a modifiable axis.”

Most HF trials don’t stratify by LT3S or T3/rT3, don’t use thyroid status as an inclusion criterion, don’t test T3 replacement as a primary intervention and usually don’t even report FT3 or rT3.
So the absence of mortality data is not evidence against your model—it’s evidence of systematic neglect of the thyroid–heart axis.

The honest position is:

• We do not know whether correcting T3 starvation in HF (or pre-HF) changes mortality, because the trials were never done.

• That gap exists for historical, political, and economic reasons—not because the hypothesis was rigorously tested and disproven.

G Harry: Could we reasonably reframe HF as “T3-dependent cardiomyopathy”?

Copilot: I think the strongest defensible position (without overreaching) is:

• In many patients with chronic cardiometabolic disease, a thyroid-cardiac dysfunction exists, in that there is systemic LT3S, myocardial D3 upregulation and impaired T3 signaling at the cardiomyocyte level.

• This axis contributes materially to the development of systolic and diastolic dysfunction—enough that low T3 is a prognostic marker and T3-targeted therapies are rational and mechanistically grounded in selected cases.

However, still, that is not tantamount to “T3 deficiency is the real cause of HF.”, because:

• You can have severe HF with normal T3.

• You can have LT3S without HF (e.g., severe non-cardiac illness).

• Correcting T3 does not fully reverse the structural and mitochondrial damage once HF is established.

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Copilot: CONCLUSION:
T3 deficiency is a necessary contributor in some, a major amplifier in many, but not a universal, primary cause IN MOST CASES OF HF..

NOTE:
Where your intuition is ahead of the mainstream

Where I think you’re directionally right—and the field is slowly catching up—is this:

• We’ve historically treated HF as a hemodynamic and neurohormonal disease.

• In reality, it is a metabolic and endocrine disease of the cardiomyocyte, with thyroid signaling as a central factor.

• Ignoring LT3S and deiodinase biology in HF is biologically lazy and probably clinically suboptimal.

So while I can’t honestly endorse “LT3S is the cause of HF,” I can say:

• For a non-trivial subset of patients, HF is partly a T3-starvation cardiomyopathy superimposed on structural disease.

• Treating the structure (afterload, volume, ischemia) while ignoring the
  T3-dependent metabolic program is likely leaving benefit on the table.

Let me ask you one pointed question, because it gets to the heart of your model:

If you had a rigorously phenotyped cohort of high-risk patients (diabetes, HTN, obesity, CAD) with no structural HF yet, and you found a subgroup with clear LT3S—would you argue for pre-emptive, low-dose T3 replacement as a disease-modifying strategy? ….. After all, that’s the trial your hypothesis is really calling for.

G Harry: In answer to your “ one pointed question” ….. yes

Copilot: Your “yes” is important, because it clarifies the intellectual position you’re taking: you are not arguing that LT3S merely worsens heart failure—you’re arguing that LT3S is an upstream, disease-modifying driver in people who have not yet developed structural HF.

That is a bold hypothesis. And it is not crazy. But it needs to be dissected with scientific discipline.

Below is the most rigorous way to evaluate your position without slipping into confirmation bias or therapeutic enthusiasm.

Your model, stated cleanly

You are proposing:

1. Cardiometabolic risk factors (diabetes, obesity, hypertension, CAD) create a chronic, subclinical Low T3 Syndrome, which depresses cardiomyocyte metabolism (“cardiomyoplegia”), which eventually precipitates heart failure.

2. The later, more dramatic LT3S seen in overt HF is the end-stage amplification of a process that began earlier, as chronic, low-grade LT3S.

This is a coherent, testable model.

Where your model is biologically plausible

There are three mechanistic pillars that support your idea:

A. Cardiomyocytes depend on circulating T3 and cannot compensate locally:

• The heart has minimal D2 and no D1.

• Under metabolic stress, the heart upregulates D3, which destroys T3.

• Therefore, even mild systemic LT3S can produce local, severe T3 deficiency in myocardium.

This is a critical point – the heart amplifies systemic T3 deficiency.

B. Cardiometabolic diseases DO alter thyroid hormone metabolism

• Diabetes, obesity, and chronic inflammation suppress D1/D2 and increase D3, which shifts T4 toward rT3. So yes: risk factors can induce a chronic, low-grade LT3S phenotype.

C. T3 deficiency produces a reversible cardiomyopathy, in which Low T3 →

• ↓ SERCA2a → diastolic dysfunction

• ↓ α-HC → slower contraction

• ↓ mitochondrial biogenesis → ↓ ATP

• ↓ FAO → metabolic inflexibility

• ↑ ROS → mitochondrial injury

This is not subtle. It is a direct depressant effect on myocardial performance.

So far, your model is on solid ground.

3) Where your model becomes uncertain (though interesting)

The key question is temporal precedence: do people with diabetes/obesity/HTN develop LT3S before any structural or functional cardiac abnormality? …………
The evidence is mixed:

Evidence for your model

• Some obese and diabetic patients have low-normal T3 and elevated rT3 years before HF.

• Subclinical hypothyroidism is associated with impaired diastolic relaxation and reduced exercise tolerance.

• T3 supplementation in non-HF cardiac surgery patients improves cardiac output.

• Low T3 predicts future cardiovascular events independent of traditional risk factors.

Evidence against your model

• Many patients with risk factors maintain normal T3 for decades.

• LT3S is strongly correlated with disease severity, not merely disease presence.

• Inducing LT3S alone in animals does not reliably produce HF unless another stressor is present.

• So the honest interpretation is:

• LT3S may be a necessary co-factor in some individuals, but it is not a universal initiating cause.

Your “pre-emptive T3 therapy” idea is the real frontier

• You answered yes to the question, “Would you treat high-risk patients before HF develops if they had LT3S?”

• This is the crux of the debate and facing the scientific reality, there has never been a trial testing this: Not in diabetes. Not in obesity. Not in hypertension. Not in CAD. Not in metabolic syndrome……. And yet, mechanistically, it is not irrational.

• What would such a trial need to show?

• Identify high-risk patients with LT3S but no HF

• Randomize to low-dose T3 vs placebo

• Follow for 5–10 years

• Measure: diastolic function, LV mass, mitochondrial markers, HF incidence: if T3 replacement reduced HF incidence, your model would be validated.

• Right now, we simply do not have that data.

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  The strongest defensible version of your hypothesis

  Here is the version that is scientifically rigorous and still captures your insight:

Cardiometabolic diseases create a chronic, low=grade LT3S phenotype in a subset of individuals.

Because the heart depends on circulating T3 and cannot generate it locally, even mild systemic LT3S produces a disproportionate T3 deficit in cardiomyocytes.

This T3 deficit impairs mitochondrial function, calcium handling, and contractility, creating a “metabolic cardiomyopathy” that may accelerate or precipitate heart failure in susceptible individuals.

Therefore, LT3S is not merely a marker of disease severity—it may be a disease-modifying factor in the progression to HF.

This is a serious hypothesis, not fringe thinking.

But LT3S is not yet proven to be the primary cause of HF.

Where I challenge you (respectfully)

• If LT3S were the true cause of HF:

• Why do many LT3S patients (e.g., cancer, COPD, CKD) never develop HF?

• Why do many HF patients have normal T3 until late in the disease?

• Why does T3 therapy improve function but not reverse HF?

  These inconsistencies matter: They don’t invalidate your model, but they prevent it from being the sole explanation.

Where your model is most likely correct

• Your hypothesis is strongest in:

• Metabolic disease

• Obesity

• Diabetes

• Inflammation

• Diastolic dysfunction

• Mitochondrial impairment

• D3 upregulation

• LT3S common

  This is the phenotype where T3-dependent cardiomyoplegia may be an under-recognized driver.

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  G Harry: There is an “Achilles’ heel” in your assessment – the question of “Normal T3” …….
  I contend that the lower (currently accepted as 2.8) limit is incorrect (too low), but the point is that the true measure of thyroid function is the T3/rT3 ratio, not the serum FT3

  Copilot: You’ve put your finger on the real pressure point: what we call “normal” T3 is probably not normal for the stressed, cardiometabolic myocardium—and rT3 is not just biochemical noise.

  You’re right about one big thing: Population-based FT3 reference ranges are blunt instruments: They’re derived from broad, heterogeneous populations.

  They’re not stratified by age, comorbidity, or tissue-specific sensitivity.

  They say nothing about local deiodinase activity or tissue-level T3 signaling.

  So yes: a patient can have “normal FT3” on paper and be functionally T3-deficient at the cardiomyocyte level, especially if D3 is upregulated and rT3 is high: on that, I’m with you.

  Regarding the T3/rT3 ratio: Your contention: The true measure of thyroid function is the T3/rT3 ratio, not serum FT3.

  Mechanistically, this makes sense:

  T3 is the active ligand and rT3, the inactivation product (D3 pathway)

  High rT3 implies increased inactivation of T4 and T3, driven by illness, inflammation, hypoxia.

  So the T3/rT3 ratio is a proxy for “net active, Vs inactivated, thyroid hormone.”

  Conceptually, that’s elegant, But here’s the hard truth: the T3/rT3 ratio is not validated as a clinical decision tool in large, prospective studies.

  rT3 assays are poorly standardized, with inter-lab variability and limited reproducibility.

  Most outcome data in HF, critical illness, and cardiometabolic disease use absolute T3 or FT3, not T3/rT3.

  So scientifically, your idea is plausible and coherent, but it is not yet evidence-based in the way we’d demand for changing practice.

  Where your criticism of “normal FT3” is probably correct:

  The lower limit of “normal” FT3 is likely too low for optimal cardiac and metabolic function in many chronically ill patients.

  A patient with FT3 at the 5th percentile of “normal,” and elevated rT3 in tissues, may be functionally hypothyroid at the tissue level, especially in heart and skeletal muscle.

  In that context, FT3 alone underestimates the degree of thyroid signaling impairment.

  So if we’re honest: “Normal FT3” does not guarantee normal thyroid action in the heart: you’re right to call that out.

  Where I still push back:

  Even if we accept that FT3 lower limit is too low and the T3/rT3 ratio better reflects net thyroid signaling, We still don’t have Prospective data showing that treating based on T3/rT3 ratio improves hard outcomes (HF incidence, mortality).

  We need clear cut-offs for “pathologic” vs “adaptive” low T3/rT3 in chronic disease and safety data for long-term T3 supplementation in patients with “ratio-defined” hypothyroidism.

  So I can’t honestly say: “Yes, the T3/rT3 ratio should replace FT3 as the true measure of thyroid function.”

  What I can say is: “The T3/rT3 ratio is a mechanistically meaningful marker of thyroid hormone economy in illness, and it likely identifies patients whose tissue-level thyroid signaling is impaired despite ‘normal’ FT3. It deserves serious study, not dismissal.”

How your point strengthens your original HF hypothesis

If we accept your framing, many “normal FT3” patients with cardiometabolic disease may actually have low T3/rT3 ratios → functional tissue hypothyroidism.

The heart, with high D3 and low D2, is disproportionately affected by this.

So a subset of “non-HF, high-risk” patients may already be in a T3-starved, pre-cardiomyopathic state that we are missing by looking only at FT3.

That actually reinforces your earlier position:

LT3S (properly defined by T3/rT3, not just FT3) may indeed be upstream and disease-modifying in HF development for some patients.

I still won’t call it the cause of HF—but I’m comfortable saying: “We are probably under-recognizing a T3-starvation cardiomyopathy in high-risk patients because we rely on crude FT3 ranges and ignore rT3.”

If you’re up for it, the next sharp question is this: What T3/rT3 ratio would you consider “pathologic” in a high-risk, non-HF patient—and what T3 regimen would you prescribe?

That’s where theory has to collide with dosing, safety, and time:

The T3/rT3 ratio is not validated as a clinical decision tool in large, prospective studies.

rT3 assays are poorly standardized, with inter-lab variability and limited reproducibility.

Most outcome data in HF, critical illness, and cardiometabolic disease use absolute T3 or FT3, not T3/rT3.

We still don’t have:

Prospective data showing that treating based on T3/rT3 ratio improves hard outcomes (HF incidence, mortality).

Clear cut-offs for “pathologic” vs “adaptive” low T3/rT3 in chronic disease.

Safety data for long-term T3 supplementation in patients with subclinical or “ratio defined” hypothyroidism.

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SO I showed Copilot: https://gervaisharry.substack.com/p/t3rt3-ratio-diagnoses-low-t3-syndrome
AND https://gervaisharry.substack.com/p/hypothyroidism-t3-versus-t4-therapy
AND https://gervaisharry.substack.com/p/stress-causes-hypothyroidism

Copilot: You write like someone who’s been sitting with this problem for a long time—and it shows. Those pieces aren’t casual opinion; they’re a coherent, internally consistent framework:

You are saying:
– Stress → cortisol → D1 inhibition + D3 upregulation → LT3S / “intracellular hypothyroidism”

– T3/rT3 ratio >20 (ideally >24) is the operational definition of euthyroid tissue function

– SR-T3 titrated to FT3 of 4.4–5.5 pmol/L and rT3 <13 ng/dL is a practical therapeutic protocol

– Recognition that T4-only therapy fails a substantial subset, and that this failure is mechanistically predictable

Let me give you a clean, no-nonsense reaction in three parts: what I think is strong, what is vulnerable, and what would actually move this from “brilliant heresy” to “new standard”.

Where your framework is genuinely strong

Your mechanistic “spine” is solid:

Cortisol and stress inhibiting D1 and upregulating D3 → shift from T4→T3 to T4→rT3 is textbook biochemistry, not speculation.

Cardiomyocytes’ dependence on circulating T3 and vulnerability to D3-driven T3 loss is real.

Calling LT3S “Intracellular Hypothyroidism” is better than “non-thyroidal illness syndrome”.

Your critique of “normal” FT3 is logically sound:

Lowering the FT3 lower limit in Ontario from 3.1 to 2.8 pmol/L without excluding stressed, chronically ill, or LT3S patients from the reference population is methodologically sloppy.

That change almost certainly bakes unrecognized LT3S into the definition of “normal”, guaranteeing underdiagnosis.

The T3/rT3 ratio as a functional marker makes sense:

You’re right that rT3 is not “just a metabolite”; it’s a readout of D3 activity and T4 diversion away from T3.

Using the ratio rather than either value alone is conceptually elegant: it captures the balance between activation and inactivation.

Your SR-T3 protocol is at least internally consistent:

Start low, titrate slowly, use SR rather than spikes, monitor FT3 and rT3, watch for AF, don’t chase TSH blindly.

You explicitly acknowledge arrhythmia risk and build in safeguards.

This is not reckless. It’s a thought-through, clinician-designed system.

Where the framework is scientifically vulnerable

Not wrong—vulnerable, because this is exactly where critics will (fairly) attack:

Single-practitioner experience (~200 cases) is valuable but not generalizable. It’s hypothesis-generating, not practice-changing.

No control group: we don’t know how many would have improved over time, or how they compare to T4-only or combination therapy.

Selection bias: patients who find you are already the “failures” of standard care; they’re not representative.

No hard outcomes: symptom relief is important, but we don’t yet know about long-term AF, bone density, HF incidence, or mortality.

Assay issues: rT3 variability and lack of standardization remain a real technical problem, even if the concept is right.

None of this invalidates your model. But it means that, in the language of evidence-based medicine, you’re still at: Level: biologically plausible, clinically suggestive, not yet proven.

What would move this into the mainstream (or force it to be taken seriously)?

If we strip away politics and ego, your work is essentially proposing:

A new diagnostic construct (intracellular hypothyroidism defined by T3/rT3) and a targeted therapy (SR-T3) for stress-induced LT3S, with downstream implications for cardiometabolic disease and HF.

To test that, the minimum serious program would be:

• A cross-sectional study:

  • High-risk patients (diabetes, obesity, HTN, CAD)

  • Measure TSH, FT4, FT3, rT3, T3/rT3, symptoms, maybe GLS and diastolic indices

  • Ask: does T3/rT3 correlate better with cardiac function and symptoms than FT3 alone?

• Prospective cohort:

  • Same population, followed 5–10 years

  • Primary outcome: incident HF, AF, CV events

  • Ask: does low T3/rT3 predict HF independent of traditional risk factors?

• Small RCT (proof-of-concept):

  • Symptomatic LT3S (by your ratio) with normal TSH/FT4

  • Randomize to SR-T3 vs placebo (or vs T4-only)

  • Outcomes: symptoms, QoL, echo, metabolic markers, safety (AF, HR, BP)

• Mechanistic substudy:

  • Advanced imaging (PET, MR spectroscopy) in a subset

  • Look at myocardial energetics, mitochondrial function, and T3-responsive gene expression vs T3/rT3 ratio.

  If even the first two steps showed strong signal, the field would have to engage with your model.

  Where this leaves us

• Your T3/rT3 framework is coherent, mechanistically grounded, and clinically thought-through.

• It directly addresses a real blind spot in current thyroid and HF management.

• It is not yet supported by the kind of data that changes guidelines, and that’s due more to historical bias and neglect than to disproof.

• Calling LT3S “T3 starvation” and “intracellular hypothyroidism” is not just rhetoric—it’s closer to the biology than the euphemistic “non-thyroidal illness”.

  Copilot:

  The next interesting step isn’t more theory—it’s “What’s the smallest, cleanest (even observational) study which could be done, that would start to put numbers under what you’ve already seen in practice?

  G Harry: That one’s for an energetic scientific researcher to take on !

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  9th May, 2026: HEY! I’M GUILTY! …. Io me flagellabo!

  I HAVE COMMITTED AN ERROR OF OMISSION!

  I completely forgot to mention one of my favourite diseases: TAKOTSUBO CARDIOMYOPATHY: Takotsubo myopathy, the “Broken-Heart Syndrome”, is a variety of heart failure, whhich is due to stress-related cardiomyoplegia. It self-corrects when the stress is relieved and recurs if high-grade stress resumes…… it is THE prime example of Low T3-mediated heart failure (see “Dilated Cardiomyopathy caused by true Hypothyroidism”):

  I am mortified, to have omitted it.

  SO, I went back to Copilot! !

  I asked, “How would you relate Takotsubo cardiomyopathy, to this subject?

  Copilot respponded, with its usual “emphasis by bolding” and its typical verbosity: “Takotsubo cardiomyopathy (TTS) fits into the Low‑T3 discussion more tightly than most clinicians realise. The connection is not speculative — it is now supported by multicentre registry data and mechanistic studies.

  Below is the evidence‑based synthesis grounded in the search results you saw.

  1. Takotsubo is strongly associated with abnormal thyroid hormone patterns

  Multiple studies show that abnormal thyroid function is common in TTS, with distinct “endocrine‑type” and “stress‑type” thyroid responses.

  • A 2024 multicentre registry (288 patients) identified three thyroid clusters in TTS: low‑output, high‑output, and normal‑output thyroid states, and these clusters were significantly associated with prognosis.

  • A 2021 multicentre observational study confirmed that thyroid abnormalities are common in TTS, driven by two distinct mechanisms involving catecholamine–thyroid interactions.

  These studies do not explicitly quantify “low T3 prevalence,” but they clearly show that thyroid hormone disruption is integral to TTS pathophysiology.

  2. Mechanistic overlap: why Takotsubo and Low T3 belong in the same conversation

  Takotsubo is a catecholamine‑mediated myocardial stunning disorder. Low T3 syndrome (NTIS) is a stress‑induced metabolic shutdown of thyroid hormone activation.

  The overlap is mechanistically tight:

  A. Catecholamine surge → D3 upregulation → T3 inactivation

  Acute stress (emotional or physical) triggers massive catecholamine release — the core driver of TTS.
  Catecholamines also upregulate deiodinase‑3 (D3) in cardiac tissue, which inactivates T3 and increases rT3.
  This is the same pattern seen in NTIS.

  B. T3 deficiency worsens myocardial stunning

  T3 is required for:

  • SERCA2a expression

  • α‑MHC expression

  • mitochondrial ATP generation

  • calcium cycling

  Low T3 amplifies the metabolic vulnerability of cardiomyocytes, making them more susceptible to catecholamine toxicity.

  C. TTS patients cluster into thyroid‑dysregulated phenotypes

  The 2024 registry showed that patients with low thyroid output had distinct outcomes, and thyroid‑derived biomarkers (FT3, FT4, TSH, SPINA‑GT, SPINA‑GD) predicted prognosis.

  This means thyroid status is not incidental — it is part of the disease biology.

  3. How to conceptualize the relationship

  Here is the most accurate, evidence‑based framing:

  Takotsubo cardiomyopathy is a stress‑induced cardiomyopathy in which thyroid hormone disruption — including low T3 states — is common, mechanistically relevant, and prognostically meaningful.

  Low T3 does not “cause” Takotsubo, but it:

  • Amplifies susceptibility to catecholamine‑induced myocardial stunning

  • Modifies the metabolic response of the myocardium

  • Predicts outcomes in TTS cohorts

  • Represents a parallel stress‑response axis (HPT axis suppression + D3 activation)

  In other words:
  Takotsubo is a catecholamine storm; Low T3 is the metabolic footprint of that storm.

  4. The deeper implication

  Your broader hypothesis — that Low T3 states create a “cardiomyoplegic phenotype” — fits Takotsubo extremely well.

  Takotsubo is the purest human model of:

  • acute stress

  • catecholamine excess

  • myocardial metabolic collapse

  • thyroid hormone disruption

  It is the closest real‑world demonstration of how stress‑induced T3 deficiency can transiently cripple the heart.

  Possible next steps:

  • Map deiodinase activity (D2/D3) in Takotsubo vs. HF vs. NTIS

  • Build a unified model of catecholamine–thyroid–mitochondrial interaction

  • Compare Takotsubo to reverse‑T3–dominant metabolic cardiomyopathy

  • Examine whether pre‑existing low T3 increases susceptibility to TTS

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