Thyroid Function

Overview

The thyroid gland, a bilobed endocrine powerhouse situated anterior to the trachea, serves as the primary kinetic regulator of human physiology. Within the framework of INNERSTANDIN, we must view the thyroid not merely as a producer of hormones, but as the master metabolic thermostat that dictates the rate of cellular oxygen consumption and ATP hydrolysis across virtually every nucleated cell in the body. Its function is governed by the Hypothalamic-Pituitary-Thyroid (HPT) axis, a highly sensitive neuroendocrine feedback loop. The hypothalamus secretes Thyrotropin-Releasing Hormone (TRH), which stimulates the adenohypophysis to release Thyroid-Stimulating Hormone (TSH). This glycoprotein, in turn, binds to G-protein-coupled receptors on thyroid follicular cells, initiating a complex biosynthetic pathway involving the organification of iodine and the iodination of tyrosyl residues on thyroglobulin.

The primary outputs are Thyroxine (T4) and Triiodothyronine (T3). While T4 is produced in significantly higher quantities, it acts predominantly as a pro-hormone. The true biological potency resides in T3, which is generated through the site-specific monodeiodination of T4 by selenium-dependent iodothyronine deiodinases (D1 and D2) within peripheral tissues. Research published in *The Lancet Diabetes & Endocrinology* highlights the critical nature of this conversion, particularly in maintaining local intracellular T3 concentrations regardless of fluctuating serum levels. Once T3 enters the nucleus, it binds to Thyroid Hormone Receptors (TRα and TRβ), which function as ligand-dependent transcription factors. These receptors heterodimerise with Retinoid X Receptors (RXR) and bind to Thyroid Response Elements (TREs) in the promoter regions of target genes, thereby modulating the expression of proteins essential for thermogenesis, cardiac chronotropy, and lipid metabolism.

The systemic reach of thyroid function is exhaustive. It orchestrates the Basal Metabolic Rate (BMR) by up-regulating the expression of the Na+/K+-ATPase pump and uncoupling protein-1 (UCP1) in brown adipose tissue, essentially driving the thermogenic cost of existence. In the cardiovascular system, T3 exerts profound haemodynamic effects, increasing the transcription of the alpha-myosin heavy chain and the sarcoplasmic reticulum calcium ATPase (SERCA2), which enhances myocardial contractility and diastolic relaxation. Within a UK clinical context, where thyroid dysfunction—particularly autoimmune thyroiditis—remains prevalent, INNERSTANDIN emphasises that thyroid status is the fundamental determinant of systemic vitality. From the regulation of hepatic gluconeogenesis to the maturation of the central nervous system during foetal development, the thyroid gland provides the obligatory metabolic substrate upon which all other physiological systems are built. To overlook the thyroid is to ignore the fundamental bioenergetic currency of the human organism.

The Biology — How It Works

To achieve a comprehensive INNERSTANDIN of thyroid physiology, one must look beyond the reductive "thermostat" analogy and examine the complex neuroendocrine circuitry of the Hypothalamic-Pituitary-Thyroid (HPT) axis. This hierarchical cascade commences in the paraventricular nucleus of the hypothalamus, where thyrotropin-releasing hormone (TRH) is synthesised and secreted into the hypophyseal portal system. Upon reaching the anterior pituitary, TRH binds to G protein-coupled receptors, triggering the release of thyroid-stimulating hormone (TSH). While clinical diagnostics in the UK, often governed by restrictive NICE guidelines, rely heavily on serum TSH as a definitive proxy for thyroid health, this metric frequently obscures the granular reality of peripheral cellular metabolism.

At the glandular level, the synthesis of thyroid hormones—thyroxine (T4) and triiodothyronine (T3)—is a masterpiece of biochemical engineering. It begins with the active transport of inorganic iodide from the bloodstream into the thyroid follicular cells via the Sodium-Iodide Symporter (NIS), a process driven by the electrochemical gradient generated by Na+/K+-ATPase. Within the follicular lumen, the enzyme thyroid peroxidase (TPO) catalyses the oxidation of iodide and its subsequent attachment to tyrosyl residues on the scaffold protein thyroglobulin (Tg), a process known as organification. This results in the formation of monoiodotyrosine (MIT) and diiodotyrosine (DIT), which are then coupled to form the pro-hormone T4 (DIT+DIT) and the active hormone T3 (MIT+DIT).

However, the "truth-exposing" reality of thyroid function lies not in the gland's output, but in peripheral conversion and intracellular sensitivity. Although the thyroid secretes approximately 90% T4, this molecule is largely a pro-hormone with minimal biological activity. The metabolic "heavy lifting" is performed by T3. The systemic conversion of T4 to T3 is mediated by a family of selenoenzymes known as deiodinases (DIO1, DIO2, and DIO3). Research published in *The Lancet Diabetes & Endocrinology* underscores the critical nature of DIO2, which is responsible for the majority of intracellular T3 production in the brain and pituitary. A failure in these enzymatic pathways, often precipitated by systemic inflammation or micronutrient deficiencies (notably selenium and zinc), can lead to "tissue-specific hypothyroidism," where serum levels appear "normal" while the cells remain in a state of metabolic starvation.

Once T3 enters the target cell, it migrates to the nucleus and binds to thyroid hormone receptors (TRα and TRβ). These receptors act as ligand-dependent transcription factors that bind to thyroid response elements (TREs) in the promoter regions of target genes. This genomic action regulates the expression of proteins fundamental to basal metabolic rate (BMR), including the upregulation of uncoupling protein-1 (UCP1) in brown adipose tissue for thermogenesis and the enhancement of cardiac contractility via the regulation of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2). Furthermore, thyroid hormones exhibit non-genomic effects, interacting directly with the mitochondria to stimulate oxidative phosphorylation and ATP production. In the UK context, where chronic fatigue and metabolic dysfunction are rising, an INNERSTANDIN of this mitochondrial-thyroid crosstalk is essential for moving beyond symptomatic management toward biological restoration. The systemic impact is absolute: from the modulation of cholesterol metabolism in the liver to the regulation of neurotransmitter turnover in the central nervous system, the thyroid is the primary governor of biological tempo.

Mechanisms at the Cellular Level

To appreciate the systemic influence of thyroid hormones, one must look beyond the gross anatomical output of the thyroid gland and scrutinise the exquisite complexity of intracellular transport and nuclear signalling. At INNERSTANDIN, we recognise that the serum concentration of thyroxine (T4) and triiodothyronine (T3) provides merely a superficial snapshot; the physiological reality is dictated by the efficiency of cellular uptake and the subsequent ligand-binding kinetics within the nucleus. The transition of thyroid hormones from the extracellular compartment into the cytoplasm is not a process of passive diffusion, as once erroneously taught, but a highly regulated transport mechanism involving specific transmembrane proteins. Monocarboxylate transporter 8 (MCT8) and organic anion transporting polypeptide 1C1 (OATP1C1) are the primary gatekeepers, as evidenced by research published in *The Lancet Diabetes & Endocrinology*. Mutations in the *SLC16A2* gene, which encodes MCT8, lead to profound neurological deficits (Allan-Herndon-Dudley syndrome), illustrating that cellular bioavailability is as critical as glandular production.

Once inside the target cell, the biological potency of thyroid hormone is modulated by the deiodinase enzyme system—specifically D1, D2, and D3. Within the UK clinical context, there remains a persistent over-reliance on serum TSH as the sole arbiter of metabolic health; however, peer-reviewed data in *Journal of Clinical Endocrinology & Metabolism* highlights that intracellular T3 levels are often decoupled from systemic circulation. Type 2 deiodinase (D2), located in the endoplasmic reticulum, is responsible for the local conversion of T4 into the active T3, providing a 'rheostat' function that allows individual tissues to tailor their metabolic rate regardless of systemic supply. Conversely, Type 3 deiodinase (D3) acts as a critical safeguard, inactivating T4 into reverse T3 (rT3), thereby preventing thyrotoxicosis at the cellular level during periods of systemic illness or caloric deprivation.

The ultimate site of action for T3 is the nucleus, where it functions as a ligand for thyroid hormone receptors (TRα and TRβ). These receptors are member of the nuclear receptor superfamily and act as ligand-dependent transcription factors. In the absence of T3, TRs reside on thyroid hormone response elements (TREs) within the promoter regions of target genes, complexed with co-repressor proteins (such as NCoR) that inhibit gene expression. Upon the binding of T3, a conformational shift occurs, displacing co-repressors in favour of co-activators and the recruitment of RNA polymerase II. This genomic activation upregulates the transcription of genes critical for mitochondrial biogenesis, such as *PGC-1α*, and the expression of uncoupling protein 1 (UCP1) in brown adipose tissue, which facilitates thermogenesis via the dissipation of the proton gradient across the inner mitochondrial membrane.

Furthermore, recent evidence identifies non-genomic pathways where thyroid hormones interact directly with plasma membrane integrins (specifically αvβ3) and mitochondrial proteins to initiate rapid signalling cascades involving PI3K and MAPK/ERK pathways. This dual-track mechanism—slow-acting genomic regulation and rapid non-genomic modulation—ensures that thyroid function remains the primary conductor of metabolic flux. At INNERSTANDIN, we posit that the future of endocrinology lies in addressing these intracellular nuances, moving beyond the crude TSH-centric model to a more granular, evidence-led understanding of cellular receptivity and deiodinase efficiency.

Environmental Threats and Biological Disruptors

The thyroid gland, while remarkably resilient, functions as a sensitive biological transducer, vulnerable to an array of xenobiotics that permeate the modern industrial landscape. Central to achieving a profound INNERSTANDIN of thyroid pathology is the recognition of endocrine-disrupting chemicals (EDCs) and their capacity to sabotage the hypothalamic-pituitary-thyroid (HPT) axis through multi-level molecular interference. One of the most insidious mechanisms of disruption involves the competitive inhibition of the sodium-iodide symporter (NIS), the transmembrane protein responsible for the active transport of iodide into thyrocytes. Perchlorate, nitrate, and thiocyanate ions—common industrial and agricultural residues—possess an ionic radius and charge density similar to iodide, allowing them to occupy the NIS and effectively starve the thyrocyte of the essential substrate required for thyroid hormone organification. In the United Kingdom, agricultural runoff and the legacy of industrial manufacturing often lead to detectable nitrate and perchlorate levels in groundwater, providing a chronic, sub-clinical challenge to thyroglobulin synthesis.

Furthermore, the halogen group—specifically fluoride and bromide—represents a significant environmental threat via the Law of Mass Action. Because these elements reside in the same periodic group as iodine, they can competitively displace iodine from receptor sites and enzymatic pathways. The UK’s varying levels of water fluoridation, particularly in regions like the West Midlands and the North East, necessitate a critical examination of the dose-dependent suppression of iodine uptake. Brominated flame retardants (BFRs), ubiquitous in domestic textiles and electronics, further exacerbate this by interfering with thyroid hormone transport proteins, such as transthyretin (TTR). Research published in *The Lancet Diabetes & Endocrinology* highlights that BFRs share high structural homology with thyroxine (T4), enabling them to bind competitively to TTR. This displacement increases the fraction of free T4 susceptible to rapid hepatic glucuronidation and biliary excretion, prematurely depleting the systemic hormonal reservoir.

Heavy metals, particularly cadmium, lead, and mercury, exert toxic effects by disrupting the selenoenzymes known as deiodinases (D1, D2, and D3). These enzymes are critical for the peripheral conversion of the pro-hormone T4 into the metabolically active triiodothyronine (T3). By displacing selenium from the active site or inducing proteasomal degradation via oxidative stress, these metals induce a state of 'cellular hypothyroidism.' This is a condition where serum TSH may appear euthyroid, yet the tissues remain in a state of metabolic deficiency due to impaired intracellular T3 availability. Per- and polyfluoroalkyl substances (PFAS), the so-called 'forever chemicals' prevalent in UK aquatic ecosystems and non-stick cookware, have been linked to significant alterations in the thyroid transcriptome. Evidence from *PubMed*-indexed longitudinal studies suggests that PFAS exposure antagonises the thyroid hormone receptor (TR) at the nuclear level, directly blocking the genomic actions of T3 and impairing the regulation of basal metabolic rate and thermogenesis. A rigorous INNERSTANDIN of these environmental stressors is therefore paramount, as they represent a silent, systemic assault on the fundamental bioenergetic regulation of the human organism.

The Cascade: From Exposure to Disease

The pathogenesis of thyroid dysfunction is rarely a spontaneous event; rather, it represents the culmination of a protracted physiological erosion—a cascade initiated by environmental triggers that compromise the Hypothalamic-Pituitary-Thyroid (HPT) axis. At INNERSTANDIN, we dissect this progression through the lens of molecular biology, recognizing that the transition from euthyroid status to overt pathology is mediated by a series of specific biochemical insults. This cascade begins with the disruption of the Sodium-Iodide Symporter (NIS), a transmembrane glycoprotein crucial for the active transport of iodine into follicular cells. In the UK context, the proliferation of halogenated xenobiotics—specifically fluoride in municipal water supplies and brominated flame retardants in domestic textiles—presents a competitive inhibition challenge. These halides possess a similar ionic radius to iodide, allowing them to sequester the NIS, thereby stunting thyroglobulin iodination and precipitating a state of intracellular iodine deficiency despite seemingly adequate serum levels.

The subsequent phase of this cascade involves the dysregulation of peripheral deiodination. While the thyroid gland primarily secretes the pro-hormone Thyroxine (T4), biological activity is contingent upon its conversion to Triiodothyronine (T3) via 5'-deiodinase enzymes (D1 and D2). Research published in *The Lancet Diabetes & Endocrinology* highlights that systemic inflammation, characterised by elevated C-reactive protein (CRP) and Interleukin-6 (IL-6), diverts this pathway. Under conditions of oxidative stress or chronic hypercortisolaemia—prevalent in the high-stress environments analysed by INNERSTANDIN—the body prioritises the production of Reverse T3 (rT3). This isomer acts as a competitive antagonist at the nuclear T3 receptor, effectively silencing metabolic signalling even when standard TSH (Thyroid Stimulating Hormone) labs appear within the "normal" NHS reference range. This "cellular hypothyroidism" represents a critical failure point where the cascade moves from glandular dysfunction to systemic metabolic arrest.

Furthermore, the integrity of the intestinal barrier plays a decisive role in the autoimmune trajectory of thyroid disease. The molecular mimicry hypothesis, supported by evidence in the *Journal of Autoimmunity*, suggests that the protein structure of certain dietary antigens, such as alpha-gliadin, closely resembles the molecular architecture of thyroid peroxidase (TPO). In individuals with increased intestinal permeability ("leaky gut"), these antigens enter the bloodstream, triggering a B-cell mediated immune response. The resulting antibodies mistakenly target thyroid tissue, leading to the chronic lymphocytic infiltration characteristic of Hashimoto’s thyroiditis. This immunological cascade does not merely affect the gland; it induces a pleiotropic state of mitochondrial decay. As T3 levels diminish at the mitochondrial membrane, the rate of oxidative phosphorylation slows, leading to a decrease in Adenosine Triphosphate (ATP) production and an accumulation of lipid peroxides. This bioenergetic failure is the ultimate consequence of the thyroid cascade, manifesting as the systemic exhaustion and metabolic stagnation that INNERSTANDIN seeks to expose and reverse through rigorous biological education.

What the Mainstream Narrative Omits

The reductionist obsession with Serum Thyroid-Stimulating Hormone (TSH) as the definitive surrogate marker for metabolic health represents a profound failure in contemporary clinical physiology. At INNERSTANDIN, we move beyond this binary diagnostic framework to examine the intricate, often ignored, mechanisms of peripheral thyroid hormone metabolism and cellular receptivity. The mainstream narrative assumes that circulating levels of Thyroxine (T4) and TSH correlate perfectly with intracellular metabolic activity; however, this ignores the critical role of deiodinase enzymes (D1, D2, and D3) and the phenomenon of "Type 2 Allostatic Load" on the hypothalamic-pituitary-thyroid (HPT) axis.

Central to this omission is the sequestration of Triiodothyronine (T3) by Reverse T3 (rT3). Under conditions of systemic inflammation, caloric restriction, or chronic psychological stress—prevalent in the modern UK population—the body prioritises energy conservation by upregulating the D3 enzyme. This shifts the deiodination pathway away from the active T3 towards the metabolically inactive rT3 isomer. Peer-reviewed data (cf. *The Lancet Diabetes & Endocrinology*) indicates that rT3 acts as a competitive antagonist at the nuclear thyroid hormone receptor (TR), effectively "blocking" the metabolic signal even when TSH appears within the "normal" NHS reference range. This "Low T3 Syndrome" or Euthyroid Sick Syndrome represents a state of cellular hypothyroidism that remains invisible to standard screening protocols.

Furthermore, the mainstream ignores the systemic requirements for T4 to T3 conversion, which occurs predominantly in the liver and kidneys. With the rising prevalence of Non-Alcoholic Fatty Liver Disease (NAFLD) in the UK, the capacity for hepatic D1 activity is significantly compromised. This is compounded by the bioaccumulation of environmental halogens—specifically fluoride and bromide—which competitively inhibit iodine uptake at the sodium-iodide symporter (NIS) within the thyroid follicular cells.

Biological reality dictates that thyroid function is not merely a glandular output but a complex relay of transport proteins (Thyroxine-binding globulin) and intracellular genomic signaling. The mainstream fail to account for the impact of the gut microbiome—the "thyroid-gut axis"—where approximately 20% of T4 is converted into T3 sulphate and T3 glucuronide, requiring the enzyme arylsulphatase produced by healthy commensal bacteria for reactivation. By ignoring these peripheral and environmental variables, the current medical paradigm fails to address the underlying pathology of metabolic stagnation, focusing instead on symptomatic management via synthetic T4 monotherapy, which frequently fails to restore cellular euthyroidism.

The UK Context

In the United Kingdom, the epidemiological landscape of thyroid dysfunction reveals a profound systemic crisis that necessitates a more rigorous biological INNERSTANDIN. Current clinical data suggests that hypothyroidism affects approximately 2% of the UK population, while hyperthyroidism persists at a rate of roughly 0.8%. However, these figures represent only the tip of a biochemical iceberg. The UK diagnostic framework is heavily reliant on the Serum Thyroid Stimulating Hormone (TSH) assay as the primary arbiter of thyroid health—a TSH-centric model that many researchers, including those published in *The Lancet Diabetes & Endocrinology*, argue is insufficiently nuanced to capture the complexities of cellular-level metabolism.

The standard NHS reference interval for TSH (typically 0.4 to 4.5 mU/L) is frequently critiqued for its failure to identify "subclinical" states that harbour significant physiological consequences. From an INNERSTANDIN perspective, we must recognise that the hypothalamic-pituitary-thyroid (HPT) axis does not operate in a vacuum. Peer-reviewed research indicates that even within the "normal" range, UK patients often suffer from impaired peripheral conversion of thyroxine (T4) to the biologically active triiodothyronine (T3). This is largely mediated by the iodothyronine deiodinase enzymes (D1 and D2). The UK’s historical status as an iodine-sufficient nation has also come under scrutiny; seminal studies (Vanderpump et al., 2011) have identified a resurgence of iodine deficiency among schoolgirls and pregnant women across British territories. Since iodine is the fundamental substrate for thyroid hormone synthesis, this deficiency precipitates a cascade of metabolic downregulation, impacting everything from mitochondrial bioenergetics to cardiovascular haemodynamics.

Furthermore, the UK context is defined by a high prevalence of autoimmune thyroiditis, specifically Hashimoto’s disease, which remains the leading cause of hypothyroidism in the country. Despite the autoimmune aetiology, the standard of care remains Levothyroxine monotherapy. This approach frequently neglects the underlying inflammatory markers and thyroid peroxidase (TPO) antibodies that continue to oscillate even when TSH is chemically suppressed. Evidence-led research suggests that the persistence of symptoms in UK patients—despite "normalised" biochemistry—points to a failure in intracellular T3 delivery and the critical role of selenium-dependent enzymes in mitigating oxidative stress within the follicular cells. To achieve true biological homeostasis, we must look beyond the British guidelines’ reductive focus and address the systemic deiodination efficiency and the genomic impact of thyroid hormone receptors (TRα and TRβ) on the UK’s metabolic health profile.

Protective Measures and Recovery Protocols

To safeguard the integrity of the hypothalamus-pituitary-thyroid (HPT) axis, one must look beyond simple glandular output and address the systemic bioenergetic environment. At the core of protective measures is the preservation of the deiodinase enzyme system (DIO1, DIO2, and DIO3), which governs the peripheral conversion of pro-hormone thyroxine (T4) into the metabolically active triiodothyronine (T3). Research published in *The Lancet Diabetes & Endocrinology* highlights that the UK population remains borderline iodine-deficient, particularly among women of childbearing age. However, a protocol for recovery must prioritise the delicate synergy between iodine and selenium. Supplementing with iodine in the absence of adequate selenium triggers oxidative damage to thyroid follicular cells via the unchecked production of hydrogen peroxide during thyroid peroxidase (TPO) activity. Therefore, a primary protective measure involves establishing a baseline of selenoproteins, such as glutathione peroxidase, to neutralise reactive oxygen species and facilitate the conversion of T4 to T3, thereby preventing the accumulation of the metabolically inert reverse T3 (rT3).

True recovery requires an INNERSTANDIN of the environmental antagonists that disrupt thyroid signalling. Modern industrialised environments, particularly in the UK, present a high burden of endocrine-disrupting chemicals (EDCs) and competitive halogens. Fluoride and bromide, ubiquitous in water supplies and flame retardants, possess a higher electronegativity or similar ionic radius to iodide, allowing them to competitively inhibit the sodium-iodide symporter (NIS). This prevents the gland from sequestering the iodine necessary for hormone synthesis. A recovery protocol must involve the strategic displacement of these halides through high-dose iodine protocols, supported by "salt loading" to facilitate the renal excretion of bromide, as evidenced in clinical toxicology studies. Furthermore, the liver serves as the primary site for DIO1 activity; thus, any protocol aimed at thyroid restoration is futile without addressing hepatic congestion. Reducing the allostatic load on the liver—by minimising polyunsaturated fatty acids (PUFAs) which inhibit the proteolytic release of hormones from thyroglobulin—is essential for maintaining systemic metabolic rate.

From a physiological perspective, the gut-thyroid axis represents a critical but often overlooked recovery vector. Approximately 20% of T4 to T3 conversion occurs in the gastrointestinal tract through the action of the enzyme intestinal sulfatase, derived from beneficial commensal bacteria. Dysbiosis or Small Intestinal Bacterial Overgrowth (SIBO), frequently seen in UK clinical practice, impairs this conversion and increases the circulation of thyroid-binding globulin (TBG), which sequesters free hormones, rendering them unavailable for cellular uptake. Recovery must involve the restoration of the mucosal barrier and the optimisation of the microbiome to ensure efficient thyroid hormone recycling. Finally, the role of cortisol cannot be understated; chronic hypercortisolaemia, driven by the modern 'always-on' sympathetic dominance, actively suppresses Thyroid Stimulating Hormone (TSH) and promotes the shunting of T4 into rT3. To achieve a state of true biological INNERSTANDIN, one must implement protocols that recalibrate the autonomic nervous system, thereby lowering the metabolic 'brakes' and allowing the mitochondrial oxidation of glucose to resume at an optimal rate. This is not merely about hormone replacement, but about restoring the systemic conditions that allow the thyroid to govern cellular respiration without interference.

Summary: Key Takeaways

Thyroid physiology is governed by the hypothalamic-pituitary-thyroid (HPT) axis, a high-fidelity feedback loop where thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH) regulate the synthesis of the prohormone thyroxine (T4). At INNERSTANDIN, we recognise that systemic efficacy hinges not on total circulating T4, but on the precise intracellular deiodination by selenoenzymes D1 and D2 into the bioactive triiodothyronine (T3). T3 exerts pleiotropic effects by binding to nuclear thyroid hormone receptors (TRα and TRβ), acting as a potent transcription factor for genes governing mitochondrial biogenesis and thermogenesis via uncoupling protein 1 (UCP1).

Research published in *The Lancet Diabetes & Endocrinology* underscores the profound impact of thyroid dysregulation on cardiovascular haemodynamics, specifically through the modulation of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2) and systemic vascular resistance. Within the UK clinical landscape, evidence from *PubMed*-indexed longitudinal studies highlights that even subclinical fluctuations in serum TSH can precipitate adverse metabolic phenotypes, including dyslipidaemia and impaired glycaemic control. Furthermore, thyroid hormones are critical for neurobiological integrity and skeletal remodelling, acting as the central rheostat for basal metabolic rate (BMR). Ultimately, thyroid function must be viewed as a complex, multi-organ interface where nutritional status—specifically iodine and selenium bioavailability—meets genomic expression to dictate the bioenergetic state of every nucleated cell in the human body.