What is Hypothyroidism? Definition and Facts

Hypothyroidism is a condition in which an underactive thyroid gland functions below its normal capacity. Such a thyroid is called a hypothyroid.

As a result of this decreased functioning of the thyroid, the levels of its hormones, tri-iodothyronine (T3) and tetraiodothyronine (T4) in the blood fall below normal and certain symptoms present themselves.

T4 forms 99% while T3 forms 1% of the thyroid hormones. However, T3 is the more biologically active hormone among the two and most of the T4 is converted into T3 after its release by the thyroid.

There are many conditions that can cause hypothyroidism, which may directly or indirectly involve the thyroid gland. It does not appear overnight but develops over years. The symptoms too, set in gradually.

Certain cases of hypothyroidism go away on their own, but, most of the time, medication is required to be taken lifelong.

The thyroid is responsible for the metabolism in the body and due to a fall in levels of thyroid hormones, the metabolism is adversely affected. This can have many adverse effects on the body. The more severe form of hypothyroidism is called Myxedema.

The thyroid is controlled by the hormonal secretion from another gland in the brain called the pituitary, which helps maintain normal levels of the thyroid hormones in the blood.

If the thyroid hormone levels fall, the pituitary secretes the thyroid stimulating hormone (TSH) to stimulate the thyroid to secrete its hormones and maintain their levels.

Hypothyroidism is fairly common, seen more in older women and can be treated with medicines

About subclinical hypothyroidism

Subclinical hypothyroidism or mild hypothyroidism is said to be present when the thyroid hormone levels are normal but the TSH is raised.

In subclinical hypothyroidism, the symptoms are absent or they may be very mild. It is usually due to lack of iodine in the body and seen more in older people.

Causes of Hypothyroidism

95% of hypothyroidism cases are caused due to some thyroid diseases. Some of these hypothyroid causes may be reversible while some may be irreversible.

1) Lack of iodine

Certain countries in general exhibit a lack of iodine in their diet. And the thyroid typically requires iodine to make its hormones.

It is by the uptake of iodine from the blood, that the thyroid is able to process its hormones, T3 and T4. Severe deficiency of iodine prevents the thyroid from making and secreting sufficient hormones. This ultimately leads to hypothyroidism.

2) Hashimoto’s disease

Hashimoto’s disease or Hashimoto’s thyroiditis (named after Dr. Hakaru Hashimoto, who first described it) is a condition wherein the thyroid gets enlarged (form a goiter) and is unable to make sufficient thyroid hormones.

This disease is caused by the autoimmune system of our body, which attacks the thyroid tissue and destroys it. The cause is unknown, but there is a hereditary trait and it does run in families. Genes are believed to play a role in its development.

3) Destruction of the thyroid tissue due to treatment for hyperthyroidism

Treatment of hyperthyroidism with radioactive iodine therapy can result in excessive damage to the thyroid cells resulting in insufficient production of T3 and T4 and hypothyroidism.

Radioactive iodine works by destroying the cells of the thyroid gland and decreasing the production of the thyroid hormones, which is needed to combat hyperthyroidism.

4) Radiation treatment

Radiation treatment given for treating other conditions such as head and neck cancers, Hodgkin’s disease, and some lymphomas can damage the thyroid gland and affect its function.

5) Thyroid surgery

Several conditions such as hyperthyroidism, goiters, thyroid nodules, and thyroid cancer are treated by surgical removal of part or the complete thyroid. This will result in hypothyroidism.

6) Certain medications cause hypothyroidism

Certain medicines used to treat hyperthyroidism like Tapezole and propylthiouracil (PTU) can cause hypothyroidism. Lithium, used in psychiatry, is also known to disrupt thyroid function.

7) Pituitary gland or hypothalamus damage

The thyroid gland function is controlled by the thyroid stimulating hormone (TSH) secreted by the pituitary gland situated in the base of the brain. The pituitary gland is, in turn, controlled by the Thyrotropin-releasing hormone (TRH) situated in the hypothalamus of the brain.

If there is damage to these two, either by a tumor or surgery or some other pathology, the thyroid function is disturbed and hypothyroidism develops.

Hypothyroidism due to pituitary damage is called “secondary hypothyroidism”, while hypothyroidism due to hypothalamus damage is called “tertiary hypothyroidism”.

Symptoms of Hypothyroidism

Hypothyroidism symptoms are due to the adverse effect that an underactive thyroid has on the metabolic activity of the body. These symptoms develop over the years.

Those patients, in whom, the hypothyroidism is mild may not even present any symptoms. But, symptoms that develop do so gradually over the years.

These symptoms are reversible and go away with treatment, exercise, and diet. Your excess body weight will go away; you will get back your hair growth and also your libido. Your fatigue will vanish and you will be yourself again.

Hypothyroid symptoms and signs include:

1) Dry itchy skin: In hypothyroidism, the blood circulation is low. In such cases, the skin receives as low as one-fourth its normal blood supply. That is why in this thyroid condition, people often have dry skin.

2) Dry hair and rapid hair loss: Due to the inadequate blood supply to the hair roots, your hair turns dry and you begin to lose hair.

3) Mental stability: Low thyroid hormones can unsettle your mental stability. You may suffer from mental slowing, memory problems, difficulty in concentration, mood swings, and a feeling of depression.

4) Disturbed sleep: 30 percent of hypothyroid patients suffer from sleep apnea, which causes disturbed sleep.

5) Weight gain in hypothyroidism is due to the slowed down metabolic rate. Your metabolism is what turns your calories into energy. A slowed down metabolism means you retain more calories causing weight gain. Treatment of this condition with medication, exercise, and a weight loss diet will get rid of the excess weight.

6) Fatigue and muscular weakness and pain are again symptoms you experience due to a slowed down metabolism and low blood circulation throughout the body.

7) Intolerance to cold weather: The thyroid gland is the thermostat of our body regulating its temperature. People with hypothyroidism tend to have low body temperatures and cold intolerance.

8) Decreased libido or loss of sex drive in hypothyroid patients is commonly seen. This is because due to the slowed down metabolism, you find that the sex organs and glands producing sex hormones, also slow down.

Both men and women can see decreased testosterone and estrogen levels. It gets corrected with thyroid treatment.

9) Constipation develops in an underactive thyroid because of the slowed down metabolism and blood circulation. Less blood supply to the gastrointestinal tract causes slowing down of its motility.

10) Menstrual changes: In addition to symptoms being mentioned above, women may experience abnormal changes in menstrual cycles.

11) Puffy eyes and face and swelling of the hands and legs due to fluid retention appear due to the slowed down blood circulation and metabolism in hypothyroidism.

12) Increased levels of cholesterol and triglycerides: Your body uses triglycerides for energy. Due to the slowed down metabolism, your body converts less of triglycerides into energy causing more triglycerides to be retained in the body.

In the same way, excess LDL cholesterol is prevented from getting rid off from the body by the dulled metabolism.

Possible dangers of hypothyroidism

If untreated, hypothyroidism causes certain complications, which can be serious.

  • Goiter. As a result of low levels of thyroid hormones in the blood, the pituitary gland secretes more of TSH in order to stimulate the thyroid to secrete more T3 and T4, which cannot happen due to the inefficient thyroid. This persistent secretion of TSH causes the thyroid to enlarge, resulting in Goiter.
  • Heart disease. A person with hypothyroidism is easily susceptible to heart problems due to increased levels of LDL cholesterol and triglycerides.
  • Infertility. Low levels of thyroid hormones interfere with ovulation, which can lead to infertility.
  • Miscarriages. A woman with untreated hypothyroidism is at the greatest risk of a miscarriage during her first trimester of pregnancy.
  • Birth defects. Women with untreated hypothyroidism face a higher risk of giving birth to children with birth defects. These babies are also more prone to serious mental and developmental problems.
  • Peripheral neuropathy. Due to a sluggish metabolism and blood circulation, the peripheral nerves face an acute short supply of blood and nutrition leading to peripheral neuropathy. This may cause pain, numbness, and tingling in the area covered by the damaged nerve. There may also be accompanying muscle weakness or loss of muscle control.
  • Myxedema. This is a serious life-threatening condition that develops as a consequence of long-standing and untreated hypothyroidism. It manifests as lethargy, drowsiness, cold intolerance and can be triggered by certain medications like sedatives, infection, and stress.

Hypothyroidism Diagnosis

Once you have been diagnosed with hypothyroidism by your symptoms, your physician will want to confirm the hypothyroidism diagnosis by advising certain blood tests.

  • Serum cholesterol and triglycerides tests will show that their levels are raised.
  • The blood count will indicate anemia. Anemia is diagnosed in 20-60% patients and is often the first sign of hypothyroidism.
  • Thyroid hormones, T3 and T4 levels will be below normal. However, in subclinical hypothyroidism, these levels may be normal. In such a case, to confirm the diagnosis of hypothyroidism, the level of TSH hormone will have to be determined, which will be raised.
  • Thyroid scan will help to find out the underlying cause of the thyroid pathology.
  • MRI of the brain is indicated if there is involvement of the pituitary or the hypothalamus.

Importance of TSH levels in hypothyroidism

As explained earlier, the pituitary gland secretes the TSH hormone to stimulate the thyroid to secrete more of its hormones, when T3, T4 levels in the blood fall. In hypothyroidism, due to decreased function of the thyroid, the pituitary is constantly secreting the TSH to stimulate the thyroid. Therefore, in hypothyroidism, TSH levels are raised.

This is seen even in subclinical cases of hypothyroidism. Therefore, increased levels of TSH with even normal levels of T3 and T4 will confirm hypothyroidism.

However, in cases of secondary hypothyroidism, (explained above), where the hypothyroidism is due to a defect in the pituitary gland, the levels of TSH will be decreased.

In such cases, the levels of the hormone secreted by the hypothalamus, the TRH is to be determined. Its level will be high as it is secreted in excess to stimulate the pituitary gland to secrete TSH.

Treatments for hypothyroidism 

Treatment of hypothyroidism involves taking thyroid medication throughout life. Frequently, the doctor may require monitoring of the thyroid hormones’ blood levels to arrive at the hypothyroid medicine and its dose, which best suit that particular hypothyroid patient.

Drugs and medicines for Hypothyroidism: Levothyroxine

Levothyroxine is the drug of choice. It is a synthetic thyroid hormone of which small doses are initially prescribed, to control the symptoms and bring the raised levels of TSH to normal.

Hormone levels are to be monitored every 2 to 3 months to establish the exact dosage required for you.

Once the dosage has been fixed, the monitoring of levels has to be carried out every year.In heart patients, the doses prescribed are usually smaller. But, medication is to be taken lifelong.

This medicine works best on an empty stomach and has to be taken in the morning about 60 minutes before breakfast or any other medicine.

Do not change the brand. If you do so, inform your physician.

If you develop any symptoms of hyperthyroidism, consult your physician, who may then have to reduce the dosage.

Patients of Myxedema can go into a coma and require hospitalization, intravenous thyroid hormones and steroids.

You should be aware of the side effects of thyroid hormone medication. Too much of it can cause

  • Increased appetite
  • Insomnia
  • Heart palpitations
  • Tremors

Hypothyroid Diet and foods to avoid

There is no such thing as a diet for hypothyroidism. Though claims are made to the contrary, there are no foods that improve the function of the thyroid.

However, there are certain foods and medicines that can impair the absorption of thyroid medication and thyroid hormone medication taken for hypothyroidism. Such foods and medications should be avoided. They are:

  • Foods containing high dietary fiber
  • Iron and multivitamin tonics
  • Calcium supplements
  • Ulcer medicines such as antacids and sucralfate
  • Certain medicines taken to lower cholesterol such as cholestyramine and colestipol
  • Cottonseed meal
  • Soybean flour

Prevention Measures for thyroid diseases are not yet established.