There thyroxine (T4), is the main hormone produced by the thyroid gland, following the stimulation of the thyrotropin hormone (TSH). Thyroxine travels in the blood bound to specific proteins, and only a small part, the free thyroxine (fT4) circulates in the blood not bound to proteins. However, free thyroxine is the fraction of the hormone that is really active, and it is also the most reliable test to carry out if you want to know the functionality of the thyroid. In the presence of high free thyroxine (fT4 high) you will have a condition of hyperthyroidism, while in the presence of a low free thyroxine value (low fT4) you will have a condition of hypothyroidism.
Free thyroxine - FT4 and T4: normal values
T4 or thyroxine: 4.5–11.2 μg / dL (58–144 nmol / L according to the SI unit of measurement, the International System Units)
fT4 or free thyroxine: 0.8–2.7 ng / dL (10–35 pmol / L according to the SI unit of measurement, the International System Units).
Free thyroxine - FT4 and T4: mechanism of action
Thyroxine: what it is for? There thyroxine is produced by thyroid, a gland located at the front of the neck. Thyroxine, one of the two thyroid hormones, is synthesized from iodine (a deficiency of iodine will therefore cause a deficiency of thyroid hormones) and dal tyrosine, an amino acid precursor to other substances such as catecholamines (dopamine, adrenaline, noradrenaline) and melanin. The main regulator of the thyroid it is TSH (Thyroid-stimulating hormone), also called thyrotropin, a hormone produced in the pituitary, which in turn is stimulated by a hormone produced at the thalamic level, TRH (thyrotropin-releasing hormone). Low levels of thyroid hormones stimulate greater production of TRH and increase TRH receptors in the pituitary cells: consequently, the pituitary gland produces greater quantities of TSH, which acts directly on the thyroid cells and on the various thyroid enzymes, resulting in greater hormone production. The reverse happens when there is too much thyroid hormone in the bloodstream.
Thyroid hormones are represented by the thyroxine (T4) for over 90%. T4 is then converted at the peripheral intracellular level by the 5-deiodinase a enzyme triiodothyronine (T3), a hormone at least 5 times more active than thyroxine. There is one for both thyroid hormones free fraction o "free" (indicated with an f before the hormone name: fT3 and fT4), and a portion bound to plasma proteins, such as thyroxine-binding globulin, TBG), albumin and the transthyretin. For example, approximately 99.7% of T3 is bound to plasma proteins, and only 0.3% is found in the form of fT3. The proteins that bind thyroid hormones are never completely saturated: TBG, for example, in physiological conditions is saturated for less than a third of its total availability. The ratio between the fraction of protein-bound thyroid hormones and the free fraction depends on the body's energy needs and on the activity of the thyroid.
In thehypothyroidism, having a total amount of thyroxine lower than normal, there will be a greater "release" of the part of thyroid hormones bound to proteins: in this way in the initial stages of hypothyroidism the free fraction may still be normal or only moderately reduced, while the bound fraction will already be strongly decreased. Usually (but not always) high TSH values are found in hypothyroidism, due to increased thyroid activation in response to low thyroxine and triodothyronine values.
In case of hyperthyroidism there will be an excessive amount of thyroid hormones in circulation: to remedy this disproportion the fraction linked to TBG and other plasma proteins will increase, trying to keep a level of thyroxine and triiodothyronine as close as possible to normal values. In hyperthyroidism, due to the hypothalamic-pituitary self-regulation mechanism which is suppressed by high thyroid hormone values, low TSH values are more common.
In some cases you may be faced with a "false hyperthyroidism”In this situation they show themselves high total values of thyroxine or triiodothyronine, but without the patient showing the typical signs and symptoms of hyperthyroidism; this is the case, for example, of pregnant women or people on therapy with drugs containing estrogen: in these situations, the high level of estrogen can increase the synthesis of TBG and consequently an increase in the amount of protein-bound thyroid hormones . The free fraction of thyroid hormones will decrease accordingly, and the thyroid, stimulated by TSH, will try to compensate by producing a greater quantity of thyroid hormones: in conclusion, in the blood tests we will have normal values of fT3 and fT4 and high values of total T3 and T4 .
In other cases, a "false hypothyroidism": This occurs during cortisone-based therapies, or in the presence of liver diseases: in both cases there may be a decreased production of TBG and other proteins binding thyroid hormones. The fraction bound to proteins will decrease, and consequently the fraction of free thyroxine and triiodothyronine will increase: this will lead to a decrease in the "productive push" exerted by the pituitary gland on the thyroid through TSH, and low total values may be found in blood tests of T3 and T4, with normal values of fT3 and fT4.
What is thyroxine used for? Thyroid hormones are essential for many primary functions of our body, such as the production of energy by controlling the enzymes responsible for energy metabolism, and the processes of growth and development of the organism.
L'effect of thyroid hormones it manifests itself for example at the heart level: in fact they possess a positive inotropic and chronotropic action, that is causes an increase in range and heart rate, allowing proper blood supply to the organs. Too low levels of fT3 and fT4 can contribute to the development of heart failure; conversely, too high levels of triiodothyronine and thyroxine will cause tachycardia and exaggerated heart pump activity.
To counterbalance the increased oxygen consumption linked to increased cardiac activity, fT3 and fT4 they also increase the availability of oxygen facilitating its release from the hemoglobin molecule, e favoring hematopoiesis, i.e. the production of red blood cells and hemoglobin, through the increased production of EPO (erythropoietin).
Thyroid hormones are essential in learning and memory processes, in keeping us reactive to stimuli external and with adequate state of vigilance.
Under the influence of thyroid hormones they come mobilize fatty substances (lipids and fatty acids) of our body and sugars (carbohydrates), contributing to thermogenesis, which is the production of heat in our body. People with thyroxine and triiodothyronine deficiency have difficulty adapting to the cold, as their bodies cannot "burn" enough substances to generate sufficient heat to maintain an adequate body temperature.
Thyroxine and triiodothyronine also promote the dermal, bone and brain development of the fetus, contributing to the ossification and growth of nerve fibers, myelination of axons and branching of dendrites and synapses, growth of the cerebral cortex and cerebellum. This is the reason why infants who have suffered from a reduced intake of fT3 and fT4 during the neonatal period may have severe mental retardation (infantile cretinism).
Triiodothyronine participates in the bone remodeling also in adults: in case of hyperthyroidism, the risk of osteoporosis increases.
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Thyroxine: what it is and why it is analyzed
Free and total thyroxine (fT4 and T4) they are measured to evaluate thyroid function and identify any alterations due to both reduced thyroid function (hypothyroidism) and increased thyroid function (hyperthyroidism); measuring the T4 and fT4 values is also useful for monitoring the appropriateness of thyroid hormone replacement therapy in case of hypothyroidism, or of suppressive therapy in case of hyperthyroidism.
There thyroxine, also called tetraiodothyronine or more commonly T4 and triiodothyronine (T3) represent the thyroid hormones, produced and secreted by the thyroid gland, a butterfly-shaped gland found on the neck. This substance has a molecular structure based on 4 iodine molecules, and is produced by the follicular cells of the thyroid starting from thyroglobulin, a precursor molecule stored in the colloid of the thyroid follicles.
This hormone is highly lipophilic, that is, it is soluble in fatty substances but does not dissolve in water and theoretically cannot be transported in the blood due to its reduced solubility. Therefore, most of the thyroxine (about three quarters) binds to the "thyroxine-binding globulin" (TBG, Thyroxine Binding Globulin), while the remainder travels in the bloodstream associated with two other plasma proteins, albumin and transthyretin.
Due to the relatively low plasma concentration of thyroid hormones, TBG is seldom saturated beyond 25-30% of its total capacity; this means that TBG is present in excess of the amount of thyroid hormones that can bind to it. Only a small part of the total amount of T4 produced by the thyroid (approximately 0.31TT) is therefore free in the blood. This is definite free thyroxine, and is often abbreviated with the initials fT4 (free T4).
To evaluate thyroid function and thyroid hormone levels with real biological activity, it is important to measure the free part in the blood, i.e. the fT4, instead of absolute levels. In fact, fT4 expresses the amount of thyroxine actually active on the body metabolism, and is independent of confounding factors such as the increase or decrease in plasma proteins that can alter the measurement of total thyroxine.
High thyroxine - FT4 and high T4
Total thyroxine (T4) is high when it exceeds 11.2 μg / dL (or the 144 nmol / L according to the SI unit of measurement, the International System Units)
Free or free thyroxine (fT4) is high when it exceeds 2.7 ng / dL (or 35 pmol / L according to the SI unit of measurement, the International System Units)
Causes of High FT4 - High Free Thyroxine
The blood values of T4 and fT4 are regulated byhypothalamus pituitary thyroid axis, a complex mechanism that regulates the production of thyroid hormones. Thanks to this mechanism, the hormones fT3 and fT4 are kept in the normal levels by thyrotropin (thyroid stimulating hormone or thyrotropin, abbreviated to TSH produced at the pituitary level, which in turn is regulated by the secretion of thyrotropin-releasing hormone (Thyrotropin releasing hormone, abbreviated to TRH) at the thalamic level.
When, for various reasons, the thyroid gland produces excess thyroid hormones, the pituitary intervenes by decreasing the production of TSH, thus decreasing the production impulse to the thyroid gland and rebalancing the values of thyroxine and triiodothyronine. As soon as the values of fT3 and fT4 return to normal, the TSH quickly returns to the normal range. Sometimes, however, this self-regulation mechanism does not work, or is not sufficient to balance the increase in thyroxine and triiodothyronine. In this case, we will have a hyperthyroidism with low TSH values. Other times, there is an abnormal production of TSH not linked to thyroid function, but which exaggerates the production of T4. In this case we will have a situation of hyperthyroidism with high levels of TSH.
The main causes of T4 and high fT4 I'm:
Basedow-Graves disease: also called diffuse toxic goiter, is an autoimmune disease caused by the presence of antibodies directed against the TSH hormone receptor. The antibody reaction prompts the thyroid to produce thyroxine and triiodothyronine in an abnormal and exaggerated way. Furthermore, this abnormal stress can cause the formation of an enlargement of the thyroid gland (thyroid goiter). Graves' disease is very frequently characterized by hyperthyroidism, and in laboratory tests by high fT4 and fT3, low TSH and anti-TSH receptor antibody positivity.
Toxic nodular goiter: it is also called Toxic adenoma or Plummer's disease, is a benign neoplasm of the thyroid gland characterized by a single nodule (uninodular goiter) or multiple nodules (multinodular goiter) which may behave as a cold, and therefore non-secretory (non-producing) nodule, but which often on the other hand, it produces large quantities of thyroid hormones in an uncontrolled and independent way from hormonal regulation. At the level of the blood test we will then have T3 / T4 and fT3 / fT4 high and low TSH levels.
Thyroiditis: is an inflammatory pathology of the thyroid gland, which can be infectious (as in the case of acute or sub-acute thyroiditis) or autoimmune (as in the case of chronic thyroiditis), which leads in the initial stages to the release of large quantities of thyroxine and triodothyronine. These diseases then evolve into a secondary phase of hypothyroidism, as the inflammation in the long run "consumes" the tissue of the thyroid gland. In autoimmune thyroiditis there is a frequent finding of anti-thyroid antibodies like them ant peroxidase thyroid and anti thyroglobulin, and on blood tests we can find Low TSH and high values of fT3 and fT4. The most frequent forms are Hashimoto's thyroiditis (which in its initial phase of hyperthyroidism is called Hashitoxicosis), postpartum thyroiditis and silent lymphocytic thyroiditis. In non-autoimmune thyroiditis (for example, De Quervain's subacute thyroiditis or in acute bacterial thyroiditis), anti-thyroid antibodies are not as frequent as in the case of autoimmune.
Too high doses of hormone replacement therapy or other drug therapy: in patients who are already taking thyroid replacement therapy, i.e. who are taking medicines containing thyroxine such as Eutirox, the response to blood tests of high fT3 and fT4 and low TSH it may be the consequence of too high a dose of the drug. Patients on amiodarone therapy, for the control of common cardiac arrhythmias, or on lithium therapy as psychoactive therapy, may also have a hormonal imbalance characterized by hyperthyroidism.
Familial non-autoimmune hyperthyroidism: this disorder is linked to the mutation of a gene that codes for the TSH receptor, and is an inherited disease. The thyroid escapes the hormonal control of the TSH produced by the pituitary, and begins to produce thyroid hormones in an abnormal way. The pituitary will decrease TSH production to try to limit the elevated levels of fT3 and fT4. We'll have blood tests then high thyroid hormones and low TSH.
Ovarian teratoma: it is a neoplastic disease of the ovaries, characterized by the growth of embryonic tissues and therefore sometimes also of thyroid tissue. This tumor can also have benign characteristics, and causes hyperthyroidism for production not thyroid of thyroxine and triodothyronine resulting TSH reduction is increase in T3 / T4 and fT3 / fT4.
Pituitary adenoma or pituitary adenoma: Sometimes the cells of the anterior pituitary lobe, the adenohypophysis, are subject to uncontrolled growth. A benign nodule is then formed at the level, called adenoma, which, if it consists of TSH-secreting cells, can produce large quantities of thyrotropin. In this case, signs and symptoms of hyperthyroidism will be present, and blood tests will be evident high values of TSH and fT4 and high fT3.
Pituitary hyperfunction: in case of hyperpituitarism, high levels of TSH or thyrotropin will be produced and released into the blood. As already seen for TSH-secreting pituitary adenoma, the affected person will suffer from defined secondary hyperthyroidism, characterized by High TSH, with high triiodothyronine and thyroxine.
TSH-producing neoplasms: some neoplasms, such as those of breasts, of the lung or delthere prostate, can abnormally produce the TSH hormone, which, once it enters the blood, will stimulate the thyroid to produce T3 and T4. This mechanism is called paraneoplastic syndrome, which is a set of signs and symptoms caused by a neoplasm in an organ far from the site of tumor development.
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High FT4 Symptoms - High Free Thyroxine
The finding of high values of thyroid hormones, and in particular of free and total thyroxine (fT4 and T4) allows to diagnose the presence of hyperthyroidism. The main symptoms in the presence of high fT4 I'm:
- increased heart rate
- difficulty in falling asleep and / or nocturnal awakening
- vision disturbances (photophobia)
- alteration of the menstrual cycle
- hot flashes
- exophthalmos and eyelid swelling
- possible presence of eyelid swelling
- intense sweating
Low thyroxine - FT4 and low T4
Total thyroxine (T4) is low when it falls below 4.5 μg / dL (or the 58 nmol / L according to the SI unit of measurement, the International System of Units)
Free or free thyroxine (fT4) is low when it falls below 0.8 ng / dL (or 10 pmol / L according to the SI unit of measurement, the International System of Units).
Causes of Low FT4 - Low Free Thyroxine
The values of T4 and fT4 are regulated by a sophisticated mechanism called hypothalamus pituitary thyroid axis, which allows the body to regulate the production of thyroid hormones. Thanks to this system, the hormones fT3 and fT4 are kept in the normal range from TSH (thyroid stimulating hormone or thyrotropin), produced at the pituitary level, which in turn is regulated by the production of TRH (Thyrotropin
releasing hormone or thyrotropin releasing hormone) at the thalamic level. When, for various reasons, the thyroid produces thyroid hormones in defect, the pituitary intervenes by increasing the secretion of TSH, so as to increase the productive impulse to the thyroid gland and to rebalance the values of thyroxine and triiodothyronine. As soon as the fT3 and fT4 values return to normal, TSH quickly returns to normal. Sometimes, however, this self-regulation mechanism does not work, or is not sufficient to fill the thyroxine and triiodothyronine deficiency. In this case, we will have a hypothyroidism with high TSH values. At other times, there is a drop in TSH production not related to thyroid function, which does not allow adequate production of T4. In this case we will have a situation of hypothyroidism with low levels of TSH.
The main causes of low T4 and low fT4 are:
Autoimmune thyroiditis: represent the most common cause of hypothyroidism, are characterized by an inflammatory process that affects the thyroid gland, secondary to an abnormal immune response caused by our own body, which does not recognize the thyroid cells and attacks them as if they were hostile organisms. Hypothyroidism from thyroiditis is characterized by high TSH values, low fT4 and the presence of high antithyroid antibody values, which are antibodies to thyroperoxidase (anti TPO or ab TPO), antibodies to TSH receptor (anti TSH) e antibodies to thyroglobulin anti TGB). The most prominent and frequent autoimmune thyroiditis with hypothyroidism is Hashimoto's Thyroiditis.
Insufficient intake iodine: the production of thyroid hormones requires iodine, the essential raw material for the synthesis of thyroxine and triodothyronine. If not enough is introduced into the body through nutrition, the thyroid will not be able to produce enough T3 and T4. In some parts of Italy, foods are less rich in iodine than indicated by the FDA, which is why table salt is added with iodine-based compounds.
Viral thyroiditis (De Quervain's thyroiditis): Thyroid inflammatory process is linked to a viral infection that causes sub-acute thyroiditis, which manifests itself in two distinct phases: at first the thyroid is stimulated by the inflammatory process and produces large quantities of thyroid hormones, resulting in TSH low in blood. Thereafter, the thyroid enters a phase of reduced activity, and is no longer able to maintain adequate levels of thyroid hormones. In this more prolonged phase, it is normal to find High TSH and decreased fT3 and fT4.
Absence of thyroid gland for surgical (thyroidectomy) or pharmacological causes: in the case of tumors or diseases that require partial or total removal of the thyroid, there will be a partial or total block in the production of thyroid hormones (low or no triiodothyronine and thyroxine). This, if not balanced by proper drug replacement therapy, will cause an increased production of TSH by the pituitary, to try to compensate for the absence of thyroxine and triiodothyronine production. In addition to surgical removal, this can also occur in the case of thyroid destruction by drugs such as radioactive iodine, or following its damage after radiation therapy (for example for radiotherapy of tumors located in the vicinity of the neck).
Congenital hypothyroidism: in some people the thyroid has a malformation from birth, causing a situation of hypothyroidism that must be corrected immediately to avoid serious consequences in the development of the child.
Storage diseases: are rare pathologies, in which substances accumulate in the thyroid that damage the tissues and make it malfunctioning. As a consequence the production of T3 and T4 will be reduced, causing a secondary pituitary response with overproduction of TSH. Among the diseases that deposit at the thyroid level we remember amyloidosis, which causes the deposit of low molecular weight proteins produced by the organism in an anomalous way that accumulate between the intracellular spaces of the gland and damage it, and hemochromatosis, characterized from iron storage.
Medicines: there are some drug therapies that can impair the production of thyroid hormones, with low total and free thyroxine blood levels, and inducing a secondary increase in blood levels of thyrotropin (TSH). Among these the most frequent is amiodarone, an iodine-rich antiarrhythmic drug that can cause both hypothyroidism and hyperthyroidism. Other drugs that can generate this side effect are interferon (used in antiviral therapy and in immunohematological therapy), and the lithium, a psychiatric drug used in the treatment of psychiatric conditions such as bipolar disorder, or in some types of headache.
Insufficient thyroid replacement hormone therapy: Patients with recognized hypothyroidism, who are on thyroid hormone replacement therapy (the most used drug is Eutirox), must have periodic blood checks to regulate the therapy. Often the dose of thyroid hormones taken is insufficient, this will be reflected in the finding of low fT4 and fT3 in the blood.
Pregnancy: during pregnancy there is an increase in placental estrogens which stimulate the production of proteins that carry the hormones T3 and T4 into the circulation. Consequently the fraction of thyroid hormones "bound" to transport proteins increases, the "free" fraction in the blood decreases, and therefore there is a decrease in fT4 in the bloodstream.
Low FT4 Symptoms - Low Free Thyroxine
The finding of low values of thyroid hormones, and in particular of free and total thyroxine (free T4 or fT4 and T4) allows us to diagnose the presence of hyperthyroidism. The main symptoms in the presence of low fT4 are:
- Low cold tolerance
- Lability of the mood
- Tendency to depression
- Fatigue and weakness
- Weight gain (tendency to gain weight)
- Dry and fragile skin
- Loss of eyebrows (especially the outer part)
- Thin and brittle nails
- Irregularity of the menstrual cycle
- Dyslipidemias (increased cholesterol)
- Memory loss
The examination is carried out starting from a blood sample obtained with a venous sampling. It is not necessary to fast before the exam. It is known that some drugs can alter the values of free and total thyroxine. Therefore, if you are taking drug therapy, it is good to warn your doctor about all the drugs you are taking.
Taking amiodarone (an iodine-based antiarrhythmic drug) can alter the production of thyroid hormones resulting in high levels of fT4 and T4. Other drugs can also modify the blood concentrations of T4 and fT4: among these we remember heparin, phenylbutazone, phenytoin, lithium, propanolol, quetiapine.
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Here are some questions that are typed on search engines and to which we have tried to give a very quick and concise answer:
- thyroxine and triiodothyronine: they are T4 and T3, the two thyroid hormones
- free thyroxine what it is for: It is the most active part of the thyroid hormone Thyroxine or T4, it is essential for the metabolism of our body
- thyroxine at 13: is a high thyroxine
- tyrosine what is it for: is an amino acid that is used for the production of thyroxine
- fasting thyroxine: thyroxine (Eutirox) should be taken on an empty stomach for at least 30 minutes
- what is thyroxine for: it is a thyroid hormone essential for the body's metabolism
- thyroxine d6: it is homeopathic, absolutely not recommended
- thyroxine and liver: it has been discovered that thyroxine but especially triiodothyronine have a strong stimulating action on the proliferation of liver cells
- thyroxine and testosterone: often used together by body builders to lose weight and increase lean mass at the same time, it should not be done absolutely is very dangerous
- tsh and thyroid: TSH is a hormone produced by the pituitary gland that stimulates the thyroid to produce thyroxine and triiodothyronine
- thyroxine and birth control pill: the contraceptive pill does not make the thyroid sluggish or speed up: the estrogens it contains could reduce the availability of thyroid hormones in the body, but a well-functioning thyroid is able to modulate its own production of thyroid hormones to cope with this effect: therefore there should be no danger of undergoing hypothyroidism or hyperthyroidism, if the thyroid is functioning well. If, on the other hand, the person who takes the birth control pill is also on replacement therapy with levothyroxine (Eutirox), it will be necessary to check the level of thyroid hormones in the blood over time. The doctor may decide on the basis of the blood values for an increase in the dosage of the replacement therapy with levothyroxine. As for the effectiveness of the contraceptive pill, however, no impairment by the replacement therapy with levothyroxine. You can rest assured that you won't get into unwanted pregnancies.
- thyroxine and somatolines: Somatoline has produced lipid-reducing creams (which aim to reduce subcutaneous fat) that contain levothyroxine: however, they have reassured all people with thyroid problems, since the systemic absorption (in circulation) of the product applied to the skin is practically zero. No variation of Eutirox or Tapazole dosages if these creams are used.
- thyroxine and pregnancy: women with hypothyroidism in substitution therapy, who are going to become pregnant should increase the dosage of levothyroxine (usually the trade name is Eutirox), especially in the first trimester, as the need for thyroid hormones increases during pregnancy. the state of prolonged hypothyroidism causes an increased risk of miscarriage. The increase of levothyroxine in pregnancy is necessary as a consequence of the weight gain of the pregnant woman, the increased volume of distribution (increase in the body fluids into which the drug spreads), the high levels of TBG (thyroxine binding protein) , the increased desiodase activity of the placenta and the possible reduced absorption of thyroxine in case of simultaneous oral iron intake. In pregnant women taking levothyroxine, to avoid hypothyroidism in the first trimester of pregnancy, it is advisable to first try to preventively maintain the TSH before conception at fairly low values, i.e. between 0.5-1.5 mIU / L. Secondly, once pregnant, increase the dosage of Levothyroxine by approximately 30% in case of autoimmune hypothyroidism and of the 50% in case of post-surgical hypothyroidism (in any case, always consult your general practitioner or gynecologist or endocrinologist before making changes in the dosage of drugs).
- thyroxine and insulin, thyroxine and blood sugar: insulin is a hormone produced by the pancreas that coordinates the absorption and utilization of carbohydrates (sugars or carbohydrates) circulating in the tissues. Carbohydrate metabolism is influenced by thyroid hormones, which always work with insulin in a biphasic manner: triiodothyronine (T3) and thyroxine (T4) improve the sensitivity of peripheral tissue cells to insulin by promoting glycogenosynthesis (i.e. the storage of glucose in stores of Glycogen); high levels of T3 and T4 instead stimulate glycogenolysis (ie the release of sugars that were previously stored in the glycogen stores) with a consequent increase in blood sugar (blood sugar).
- thyroxine and levothyroxine: Levothyroxine is the left-handed isomer of Thyroxine: in other words, it is a particular chemical form of thyroxine, the main thyroid hormone
- thyroxine and weight loss: taking thyroid hormones for weight loss is a very dangerous practice. As is known, T3 and T4 increase oxygen consumption and therefore increase the speed of metabolism, stimulate protein synthesis at the expense of sugars and carbohydrates therefore contribute to the muscle tissue formationand not of adipose tissue. Finally, thyroxine increases heart rate and breathing. Taking Eutirox to lose weight can deregulate our metabolism, expose us to the risk of dangerous hypoglycemia, arrhythmias, increase the risk of cardiovascular events.