The thyroid gland is a butterfly-shaped gland located at the front of the neck that produces three hormones: triiodothyronine (T3), thyroxine (T4) and calcitonin. The first two are of great importance. Produced from iodine and tyrosine (an amino acid), they will bind to intracellular receptors and alter the expression of certain genes, regulating an impressive number of basic functions of the body. Thyroid hormone deficiency during the development of the fetus or the early stages of growth can in particular lead to profound and irreversible mental retardation, a situation that is currently extremely rare.

The thyroid hormones regulate the metabolism mainly, that is to say our use of the energy, therefore our weight, our energy, our mood, our body temperature, our muscular function, the functioning of the heart and the vessels, our libido , the beauty of our skin, our hair, our nails, the strength of our bones or our teeth. Their production is regulated by TSH, a hormone produced by the pituitary gland. Since the thyroid acts throughout the body, misdiagnosis is frequent: hypothyroidism can be confused with depression, fibromyalgia or manifested by unusual symptoms (heart rhythm disorders, constipation, etc.).

Thyroid diseases

The diseases of the thyroid are very frequent in the world, and in particular in France. Women are more affected than men with 8 out of every 100 women who have a dysregulation of this gland after the age of 65. The causes are many and can lead to thyroid cancer as simple nodules (areas of the thyroid whose activity changes) without danger. People who have an autoimmune disease are 25% more likely than others to have thyroid disease, especially a so-called "Hashimoto's thyroiditis" disease in which the antibodies gradually destroy the gland.

In most cases, thyroid problems, whether treated surgically, radiotherapy or without treatment, eventually develop into hypothyroidism. Fortunately, there is a synthetic form of our natural hormones used to replace our T4, it is levothyroxine (also called L-T4). Problem: Many people continue to experience symptoms of hypothyroidism even with treatment and others have symptoms of hypothyroidism with normal TSH and continue to suffer. Why and how to react?

Read Hypothyroidism: Are you concerned? Test it

The problem

Levothyroxine may be one of the most prescribed drugs in the world (and unlike statins, it does not dig the hole in social security), studies show that most people who take it receive too much or too little. A finding that, alone, explains why we can continue to have unpleasant and chronic symptoms such as depression, cramps, sleep disorders, diffuse pain or difficulties in adjusting weight.
But how to determine if we take a suitable dose? In France, routine monitoring by endocrinologists is often simply a TSH assay, the production of which is naturally adjusted in proportion to the amount of thyroid hormone circulating in the blood. French laboratories generally indicate a TSH standard of between 0.3 and 5 mIU / L. A value that all specialists agree to recognize as too high. Between 1970 and 1985, the norm for TSH was considered normal between 1 and 10. For 10 years, people who had a TSH between 5 and 10 were let suffer by telling them that everything was normal and that nothing could be done. until in 1985 the standard is revised downwards between 0.3 and 6 then between 0.3 and 5 and currently between 0.3 and 3 in the United States (with these new standards the number of Americans with hypothyroidism increased from 13 to 27 million!).

Moreover, many factors can affect the TSH (stress, poor sleep, drugs, poor diet …) which explains that the rate of TSH is not always a good indicator of the thyroid function. While the High Authority for Health (HAS) recommends only the dosage of TSH in first intention, more and more specialists in the thyroid believe that thyroid tests should also include the dosage of free hormones T3 and T4 (those who circulate in the blood and are biologically active). A low level of T3L can thus signal a deficiency of thyroid function and a low rate of T4L sign hypothyroidism. In the United States, patients' associations are asking doctors to add T3L and T4L to TSH for better diagnosis of thyroid dysfunction and better management of patients.

To learn more about TSH, read: Thyroid: is TSH a good indicator of hypothyroidism?

What to do ?

If you have symptoms of hypothyroidism or hyperthyroidism you should:

  • ask your doctor for a blood test to measure TSH but also T4L and T3L (to refine the diagnosis).
  • if the value of TSH is greater than 3, ask for an increase in your treatment or a decrease if it is less than 0.2.

Some studies actually show that patients who receive L-T4 see their quality of life improve by adjusting their doses to bring the TSH below 2.5. Other studies have shown that people who have a TSH between 0.4 and 2 have a faster metabolism than those with a higher TSH, which may be an explanation for difficulties in losing weight. A slightly elevated TSH (between 4 and 10 mIU / L) also increases the risk of cardiovascular disease, hypertension and insulin resistance. On the other hand, a low TSH greatly increases the risk of osteoporosis and serious cardiac rhythm disorders, in particular below 0.1 mIU / L.

If your TSH is still in normal range (between 0.2 and 3 mIU / L), it seems possible that levothyroxine may be converted in your body to T3, which is the final active hormone. In this case, this disorder appears on a blood test with a normal TSH and a T4 and T3 slightly lowered. Your doctor may then prescribe a mixture of T4 and T3 (synthetic T3), which should lower your T3 level to the norm and make your residual symptoms go away. This specialty is delivered in pharmacy under the name of Euthyral or Cynomel.

For now, clinical trials comparing the effects of synthetic T3 alone with those of the T3-T4 combination have shown mixed results, in part because T3 increases and decreases rapidly in the blood, making it difficult to maintain therapeutic rates. "This is not the winning ticket"says endocrinologist Elizabeth McAninch (Rush University Medical Center)."I have some patients who feel better thanks to the combination T3 / T4 and othersIn the United States, pending a large-scale clinical trial comparing the effects of T4 alone, T3-T4 combination therapy and thyroid extract, physicians are increasingly open to prescribing a small dose of T3 in patients whose symptoms do not improve with T4 alone.

Read also: Foods to avoid in case of hypothyroidism

Finally, it should be noted that certain genetic variants of certain enzymes (deiodinases) can modify the feeling towards the treatment. It is therefore necessary to listen to his body rather than listening to the numbers of the blood test and adapt the doses accordingly.

A special case: hypothyroidism frustrated

If you are poorly cared for, it can also come from a particular hypothyroidism, called frustration. According to HAS, "crude hypothyroidism is defined by a TSH level> 4 mIU / l, confirmed by a second assay at 1 month, with no abnormality in the concentration of T4L (free T4)". It would affect on average between 3.4 and 10% of the population. Women and people over 60 years of age (especially those with a history of thyroid disease or treatments such as amiodarone, lithium, interferon) are at increased risk for mild hypothyroidism.

1/3 of the cases of hypothyroidism frustrate evolve towards a real hypothyroidism, which explains why it is important to diagnose it. In addition, those who suffer from it appear to be at increased risk for diabetes, cardiovascular disease, cognitive and muscular disorders, mood disorders and bone fractures. Unfortunately, to date, official indications regarding screening and hormonal substitution remain controversial.


In the end, it is important to contact your doctor. Numbers are one thing, your symptoms are another, no less important. In case of suspicion of residual symptoms, a slight increase in levothyroxine over a few months in agreement with your doctor is safe and can allow you to see a difference, as well as the T4 / T3 combination test.
Also beware of misleading symptoms: Many symptoms of hyper or hypothyroidism may be aggravated by vitamin D deficiency or other hormonal problems, two possibilities that a blood test can easily rule out.

Two books to read if your thyroid is idling: To put an end to hypothyroidism (EXTRACT HERE >>) and Thyroid, natural solutions of Dr. Philippe Veroli (EXTRACT HERE >>).

References: Institute of health monitoring. Thyroid diseases in the SUVIMAX cohort. 1994-2002.
Spencer et al. AACC Expert Access. 08/15/06. University of Southern California.
Ali J Chakera, Simon HS Pearce, Bijay Vaidya. Treatment for primary hypothyroidism: current approaches and future possibilities. Drug Devel Ther. 2012: 6.1-11.
"Doctors Hear Patients' Calls for New Approaches to Hypothyroidism", The Wall Street Journal, April 11, 2016.

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