Causes of Hypothyroidism

Hypothyroidism is an endocrine disorder caused by a deficit of thyroid hormones. Thyroid hormone deficiency can affect virtually all body functions. The intensity of this effect varies from mild to severe. Hypothyroidism is prevalent in women, especially those older than 50 years of age. When the body does not produce enough thyroid hormone, metabolic function decreases, and as it slows down, it affects some essential processes.

For example: the body becomes hugely inefficient at processing fats and carbohydrates and this, in turn, causes sudden and unexpected weight gain. Cardiac rhythm decreases and this produces a continuous sense of fatigue and lack of energy. Depression is often a common side effect of hypothyroidism. Skin becomes dry and scaly. Constipation is another common side effect. Thyroid hormone influences the regulation of essential proteins, and so hypothyroidism habitually causes muscle pain and cramps. Obviously, the symptoms depend on the severity of the disease, with mild cases presenting little to no signs at all.

Hypothyroidism can be triggered by different causes, and different classifications can be made:

1. Primary hypothyroidism: When a defect of the thyroid gland itself causes a deficiency in its production of thyroid hormones then this is known as primary hypothyroidism. The cause is the organ itself. Primary hypothyroidism can be congenital, such as when the thyroid is malformed or too small.
    
2. Secondary or central hypothyroidism: Secondary hypothyroidism occurs when, due to alterations of the pituitary gland, by tumors, for example, there is insufficient supply of the thyroid stimulating hormone (TSH). However, the thyroid gland itself is perfectly healthy. This variety of hypothyroidism is somewhat rare.
    
3. Peripheral hypothyroidism: In peripheral or tertiary hypothyroidism, there is an alteration of the hypothalamus so that it does not produce enough thyrotropin-releasing hormone (TRH). Consequently, the cycle of regulation between the brain and the thyroid is interrupted, and the thyroid is not stimulated to produce thyroid hormones. The causes can be defects in the skeletal-muscular system, tumors or infections. This alteration is extremely rare.

Is it normal for this to happen? No, hypothyroidism is not a natural condition that occurs with the onset of a certain age. This decrease in the functioning of the thyroid gland is a problem that requires medical treatment. When it is not treated there can be severe complications.

The most frequent causes of hypothyroidism:

1. Hashimoto's thyroiditis that results in progressive destruction of the thyroid as a consequence of an out of control autoimmune response. It is as if the body does not recognize the thyroid as its own, so it proceeds to attack it by releasing antibodies produced by the immune system. It is more frequent in women from the age of 40 onward, although it can occur in other age groups and males.
2. Hypothyroidism is less frequently caused by enzymatic defects, often of hereditary nature, which compromises the synthesis of thyroid hormones. Enzymatic abnormalities can occur with enlargement of the gland. Congenital defects in the development of the thyroid gland can produce congenital hypothyroidism in newborns.
3. Thyroid surgery due to nodules, hyperthyroidism or thyroid carcinoma can also cause hypothyroidism. In these cases, there is no autoimmune mechanism, but the total or partial removal of glandular tissue leads to insufficient secretion of thyroid hormones into the blood. Radioactive iodine therapy for the treatment hyperthyroidism or thyroid cancer is also a cause of hypothyroidism.
4. Ingestion of anti-thyroid drugs such as carbimazole, methimazole or propylthiouracil, and medicines rich in iodine can hinder the synthesis of thyroid hormones and generate anti-thyroid antibodies causing hypothyroidism. Lithium treatment of manic-depressive and psychotic patients has an adverse effect on the secretion of hormones from the thyroid gland which also produces a similar effect.
5. Secondary hypothyroidism, produced by the lack of secretion of TSH in the pituitary gland, is rarer. In these cases the thyroid gland is intact, but its stimulating hormone is missing, which makes it malfunction, decreasing the levels thyroid hormones in the bloodstream.
6. Postpartum Hypothyroidism is usually asymptomatic, so most of the time it is not diagnosed. Affected women will suffer hyperthyroidism and, subsequently, hypothyroidism. In most of cases, patients recover normal functioning of the thyroid gland after about a year.
7. Sub-acute Granulomatous Thyroiditis appears after a viral infection. It begins with an inflammation of the throat, accompanied by neck pain that becomes increasingly worse, and usually presents with a slight fever.
8. Chronic deficiency of dietary iodine. Iodine is a necessary chemical for the production of thyroid hormones and must be obtained from the diet since the body cannot produce iodine.
9. Damage to the pituitary gland. The pituitary gland regulates how much thyroid hormones are produced by the thyroid gland. When the pituitary has been damaged by a tumor, radiation or surgery, it will no longer give accurate instructions to the thyroid gland, and as a result, the thyroid gland will stop producing sufficient hormones.

An important note to keep in mind is that calcium supplements, or antacids that contain calcium, can interfere with the absorption of synthetic forms of thyroid hormone prescribed as treatment for hypothyroidism. This interference occurs mainly if you take your medication and calcium supplements at the same time or around the same time. You can avoid this problem if you avoid taking calcium supplements or antacids at the same time you take your thyroid treatment. Do not take any product that contains calcium, at least four hours before or after taking your prescription for hypothyroidism. Other supplements, especially those that contain iron, can also interfere with the absorption of your medications.

Finally remember that the symptoms of hypothyroidism are usually nonspecific. It should be clarified that, although this disease is commonly associated with an increase in weight, this does not always occur; and other symptoms, such as fatigue, decreased memory, hair loss, or depression, are common to many other diseases. Therefore, if a person experiences these symptoms, it is very important that consultation with their primary healthcare provider be sought immediately.  At this point laboratory tests should be done that can assess the state of the thyroid gland and the blood concentrations of all thyroid hormones.

References:

1. Dubbs, Sarah B., and Ryan Spangler. "Hypothyroidism: causes, killers, and life-saving treatments." Emergency medicine clinics of North America 32.2 (2014): 303-317.
    
2. Astwood, E. B. "The chemical nature of compounds which inhibit the function of the thyroid gland." Journal of Pharmacology and Experimental Therapeutics 78.1 (1943): 79-89.