The thyroid gland regulates normal grow, development and metabolism in the human body. It helps to regulate many functions by constantly releasing a steady amount of thyroid hormones in the bloodstream. If the body needs more energy in certain situations (growing, cold, pregnancy), the thyroid produces more hormones. It is situated at the front of the neck and it is as a butterfly shaped, with a weigh between 20 and 60 grams.
Which hormones produces
Thyroid hormone (TH) regulates metabolic rate, body temperature and tissue growth. Iodine is important to hormone thyroid synthesis, but also Selenium, Iron, Vit, A and Zinc plays an important part of TH synthesis.
The thyroid produces 3 hormones:
- Triiodothyronine (T3)
- Tetraiodothyronine (T4)
- Calcitonin
Calcitonin is a hormone that help maintain a healthy level of calcium in the blood. When the calcium level is too high, calcitonin lower it. Calcitonin in the blood can be higher in a certain type of thyroid cancer or other disease such as kidney failure.
T3 and T4 increase the basal metabolic rate with many effects as: body temperature rise, faster pulse and stronger heartbeat, food is used up more quickly because energy stored in the liver and muscles is broken down, the brain matures (in children), activation of the nervous system leads to improved concentration and faster reflexes.
Iodine is an important element of T3 and T4, but our body can’t produce this, so we need to get enough of it in our diet. We introduce iodine mainly from seafoods and iodized salt, and throw the bloodstream to bowel, they rich thyroid that use them to make hormones.
To make the exact amount of hormones, the thyroid needs the help of another gland: the pituitary gland.
Problems
Many people across the world suffer from thyroid. Genetics contributes to 70% of the risk, but environmental factors play an important role in susceptible individuals
Disorders of thyroid function are common, but symptoms of thyroid dysfunction are non-specific .
If you suffer of hyperthyroidism, that is excess of thyroid hormone, you’ll notice weight loss due to an increased resting energy expenditure, reduced cholesterol, increased lipolysis and gluconeogenesis. If you have the opposite problem, hypothyroidism, you’ll have a reduced resting energy expenditure, with gain weight. An autoimmune disease is Hashimoto’s thyroiditis (HT), caused by an interaction between genetic factors and environmental conditions.
The thyroid gland may grow in size too: sometimes individual lumps called nodules grow in the gland. A special examination, thyroid scintigraphy, can be used to check if the nodules are producing abnormal amounts of hormones (hot nodules if they make more hormones than the rest of the thyroid tissue, cold nodules if they make less). In most cases an enlarged thyroid or nodules are not caused by anything serious (only rarely cancer) but always ask your doctor.
The untreated thyroid disease can produce serious consequences especially cardiovascular diseases.
The thyroid hormone (TH) regulates metabolism through actions in the brain, white and brown fat, skeletal muscle, pancreas, liver. It promotes both lipolysis and lipogenesis.
TH action is exerted primarily via the nuclear TR (Thyroid receptor), a member of the family of thyroid hormone receptors.
Test to check the thyroid functions
There are different tests and examinations to check whether the thyroid gland is functioning normally and whether its surface, shape and size are normal.
PALPATION OF THE THYROID GLAND: the doctor feels the neck with his hands. An enlarged thyroid (goiter) can be a sign of an iodine deficiency that has not yet affected the function of the thyroid. But it could also be a sign of an overactive or underactive thyroid. So, to discover more, the doctor asks for blood test.
BLOOD TEST: the 3 most important biochemical tests are:
- TSH (thyroid stimulating hormone)
- Free T4 (free thyroxine)
- Anti-TPO antibodies (anti-thyroid peroxidase antibodies)
TRH (thyrotropin releasing hormone) from the hypothalamus stimulates the release of TSH from the pituitary gland which, in turn, regulates a variety of steps in the production of thyroid hormones.
Indeed, the reliable interpretation of thyroid function tests require an intact hypothalamic-pituitary-thyroid axis.
A change in TSH level can be an early sign of a thyroid problem. For this reason, it is common to only measure the TSH level at first. There are many situations in which a normal TSH may not reflect euthyroidism. The concentration of TSH in the blood can also be influenced by the long-term use of certain medications as diuretics, acetylsalicylic acid, steroids, thyroid medications. Ask your doctor.
Assessment of free T4 is the most commonly ordered thyroid function test.
The majority of thyroid hormone released is T4 (85%), and a smaller proportion (15%) of T3. These hormones are highly protein-bound (99.8%), with only the free components (free T3 and T4) having the ability to bind to their respective receptors. The active TH is free T3, and tissue-specific enzymes regulate the conversion of T4 to T3 (different tissues need different levels of T3.
The relationship between T3, T4 and TSH is not linear but log-linear, so with very large changes in TSH, we’ll see very small changes of free T3 and free T4.
THS level may follow the circadian rhythm, with maximal levels seen in the early morning. It may change with age and race too, and also in a same person checked every day, without a real reason why. This change does not necessarily indicate a change in thyroid function or status, but it could affect treatment decisions.
THYROID ULTRASOUND: shows whether the thyroid gland is enlarged and changes in the tissue too. If nodules are discovered with ultrasound test, other examinations may be done: scan or magnetic resonance imaging (MRI).
THYROID SCAN (SCINTIGRAPHY): a radioactive substance is injected in the body (arm vein). This substance is absorbed by the thyroid gland more in the more active areas.
FINE NEEDLE ASPIRATION: a needle inserted into the thyroid gland remove a sample of tissue or fluid. It can establish if the changes in thyroid are cancerous or benign (non-cancerous).
Dietary factors that can cause thyroid problems:
- Excess dietary iodine (in genetically susceptible individuals) from foods or medicines;
- Deficiency of iodine
- Naturally occurring goitrogens (found in legumes, plants, lithium, cabbage, cauliflower, broccoli, soy. Various procedures like soaking, washing, boiling and cooking can help in reducing the goitrogenic potency of these foods). Patients suffering from hypothyroidism can avoid consumption of raw cruciferous vegetables as cabbage, Brussels, sprouts, broccoli, cauliflower, mustard greens, kale, turnip. In addition, daily diet should include thyroid boosting foods like those rich in iodine, aminoacid tyrosine, minerals like Selenium, Zinc, Copper, Iron, various vitamins including B2, B3, B6, C and E.
- Dietary fat composition (dietary high fat intake induces thyroid disfunction);
- Green tea at high doses
- Soy and soybean products
- Cyanogenic plant foods as cauliflower, cabbage, mustard, turnip, raddish, bamboo shoot and cassava. However, cooking destroys the enzyme responsible for activation of progoitrin to goitrin.
- Selenium deficiency
- Vitamin B12 deficiency
Environmental factors:
- Organochlorine compounds found in pesticides;
- Isoflavones
- Polychlorinated biphenyls, polybrominateddiphenylethers, bisphenol-A and triclosan (may have direct action on thyroid hormone receptor);
- Perchlorates found in rocket fuels, thiocyanates and nitrates interfere with iodine uptake;
- Cosmetics: UV filter (can alter thyroid homeostasis) and OMC (Octyl-methoxycinnamate);
- heavy metals: cadmium (Cd) and lead (Pb)
- smoking
- Age (more common in perimenopausal and menopausal women cause altered balance between oestrogen and progesterone)
Deficiency of iodine
Iodine is present in soil, sea water, dairy products, seafoods, eggs and iodized salt). Recommended dietary iodine is 150 ug. For pregnants is 220 and lactating women is and 290 ug.
Urinary iodine level is the best measure to assess the iodine level in the body (deficiency if < 50 ug/ml). A deficiency of iodine can causes hypothyroidism and developmental brain damage, deaf mutism, short stature, mental retardation, in children of mothers having an iodine deficiency during pregnancy. Iodine deficiency in pregnant women is associated with miscarriage, stillbirth, preterm labor or congenital disorders in babies. The safe upper limit of iodine intake is around 1,1 mg per day. Not only iodine is the cause.
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