Underactive thyroid (hypothyroidism)

The thyroid is butterfly-shaped gland in the neck, in front of the windpipe. In adults, it is about 2cm wide and 4cm high.

The thyroid gland makes two hormones: thyroxine (also called T4) and triiodothyronine (also called T3). Together, these hormones regulate the body’s growth and metabolism, that is, how quickly the body burns energy and how quickly reactions happen inside the body. The production of thyroid hormones in the thyroid is controlled by another hormone called thyroid stimulating hormone (TSH). This is made by the pituitary gland in the brain.

Hormones are carried in the bloodstream and the purpose of the hormones of the thyroid is to keep the body’s functions (metabolism) working at the correct pace.

Hypothyroidism can affect people of any age or gender. About 1 in 50 women, and about 1 in 1000 men will have hypothyroidism at some time in their life. It becomes more common with increasing age.

Symptoms

Hypothyroidism usually develops over time. At first the symptoms are mild and may not even be noticed. Gradually they become worse over months or years as the level of thyroxine in the body gradually falls.

Some symptoms are more common than others, but not all symptoms appear in all people suffering from this condition. The common symptoms may include the following:

• • Dry, thinning, course or lifeless hair

• • Depression

• • Poor memory and loss of concentration

• • Tiredness and sleeping a lot

• • Swollen face, hands and feet, fluid retention

• • Muscle aches and pain

• • Joint pain

• • Dry skin

• • Sensitivity to cold

• • Brittle, thin fingernails

• • Constipation

• • Weight gain

• • Slower movements and speech.

The less common symptoms include the following:

• • Change in facial features

• • Thinning eyebrows

• • Reduced sense of taste and smell

• • Hoarseness or deepening of the voice

• • Slow heart rate

• • Irregular, heavy or prolonged menstrual periods in women

• • Infertility

• • Decreased libido

• • Carpel tunnel syndrome

• • Some people also have a swelling of the thyroid gland. This is called a goitre.

However, the symptoms can also be caused by other conditions, and sometimes the diagnosis is not obvious.

Causes

A number of things may cause insufficient production of thyroid hormones:

• • Autoimmune thyroiditis is one of the most likely causes of hypothyroidism. This happens when the body’s own immune system attacks the cells of the thyroid. These damaged cells can no longer produce sufficient quantities of thyroid hormones. Hashimoto’s disease is one specific autoimmune disease that causes this to happen.

• • Non-autoimmune thyroiditis is any inflammation of the thyroid gland. Apart from autoimmune problems, viral infection or pregnancy (in about 8% of pregnant women) can affect the thyroid gland. Often the thyroid becomes inflamed and first produces too much and thereafter too little thyroid hormone. This condition may lasts up to six months but the inflammation can become chronic.

• • Previous treatment for an overactive thyroid (hyperthyroidism), such as radioactive iodine therapy, thyroid surgery and certain medications, may lead to permanent insufficient hormone production.

• • Iodine deficiency is the most common cause of hypothyroidism worldwide. Iodine is needed by the body for the production of thyroid hormones. Iodine is added to table salt to help prevent iodine deficiency.

• • Certain medications can stop the thyroid gland from functioning properly. Certain cough syrups and kelp-based dietary supplements can contain too high levels of iodine, which will suppress thyroid hormone production. Other medication that may lead to hypothyroidsm include lithiumn (for bipolar disorder), amiodarone (for certain heart conditions), and carbimazole and propylthiouracil (for hyperthyroidism).

• • Inherited (conginital) hypothyroidism occurs in some children where the thyroid has not developed properly and as a result not enough thyroid hormones can be produced. With treatment, babies who have congenital hypothyroidism develop normally.

• • Problems with the hypothalamus (the part of the brain that links the nervous system to the endocrine system) and pituitary gland may cause the condition because these parts of the brain are involved in the regulation and production of thyroid hormones.

Treatment

Occasionally, hypothyroidism gets better without treatment. In general, however, the symptoms get progressively worse if it isn’t treated.

A blood test will confirm that someone has hypothyroidism and will also determine if it is caused by the insufficient hormone production of the thyroid gland, pituitary gland or hypothalamus. The specific diagnosis will determine the treatment.

Hypothyroidism caused by insufficient thyroid hormones is treated with a medicine called levothyroxine. This is a life-long treatment which involves taking a tablet on a daily basis. The tablet increases the levels of the thyroxine hormone in the body to normal levels. It takes some time to determine the dose needed to reach normal levels. Usually the initial dose is low and this is increased gradually until the level of thyroxine in the blood is equal to the level of thyroxine in the blood of someone without hypothyroidism. The thyroxine in the medicine is converted into triiodothyronine in the body and therefore no additional medication is necessary to reach adequate levels of both these hormones. Once the correct dose has been established, people usually begin to feel much better; however it is important not to stop taking the treatment. To ensure the levels of thyroxine do not get high and cause increased metabolism, regular blood tests are done.

Other medicines, such as warfarin, may have an influence on levothyroxine. Therefore discuss the medication with your doctor. Tablets should be taken on an empty stomach (before breakfast) and not at the same time as calcium or iron tablets are taken, because these substances will interfere with the absorption of levothyroxine.

With treatment, the outlook is excellent, symptoms usually disappear and complications become unlikely.

Complications of untreated hypothyroidism

When hypothyroidism is not treated, the symptoms will gradually worsen and may lead to the following:

• • Increased risk of developing heart disease. This is because low thyroxine levels cause the blood lipids (e.g. cholesterol) to rise

• • Increased risk of developing pregnancy complications such as pre-eclampsia, miscarriage, anaemia, premature labour, low birth weight, stillbirth and serious bleeding after the birth

• • Severe depression

• • Hypothyroid coma (myxoedema coma), which is a very rare complication when thyroid hormones have reach critically low levels.

Our Employee Wellbeing Programme (EAP) is available 24 hours a day if you want to know more about thyroid problems.