What is hypothyroidism?

Hypothyroidism means you have too little thyroid hormone. Another term is an “under-active thyroid.” Hypothyroidism is the most common thyroid disorder. It occurs more often in women and people over age 60. Hypothyroidism tends to run in families.
Symptoms may include:
  • Tiredness/sluggishness
  • Mental depression
  • Feeling cold
  • Weight gain (only 5–10 pounds or 2–4 kg)
  • Dry skin and hair, as well as hair loss
  • Constipation
  • Menstrual irregularities
These symptoms are not unique to hypothyroidism. A simple blood test can tell whether the symptoms are due to hypothyroidism or some other cause. People with mild hypothyroidism may not have any symptoms at all. 

What causes hypothyroidism?

In adults, Hashimoto's disease is the most common cause of hypothyroidism in industrialized countries (iodine deficiency is the most common cause in the rest of the world). In Hashimoto, your immune system attacks and damages your thyroid, so it can't make enough thyroid hormone. Hypothyroidism can also be caused by radioactive iodine treatment or surgery on the thyroid gland, which are used to treat other types of thyroid disorders. A problem with the pituitary gland is another rare cause. Congenital hypothyroidism is present from birth and occurs when the thyroid gland does not develop properly. 

How can hypothyroidism affect your health?

In adults, untreated hypothyroidism leads to poor mental and physical performance. It also can cause high blood cholesterol levels that can lead to heart disease. A life-threatening condition called myxedema coma can develop if severe hypothyroidism is left untreated.
Diagnosis of hypothyroidism is especially important in pregnancy. Untreated hypothyroidism in the mother may affect the baby's growth and brain development.
All babies are tested at birth for hypothyroidism. If not treated promptly, a child with hypothyroidism could have an intellectual disability or fail to grow normally.

Hypothyroidism and Heart Health 

Studies show that hypothyroidism can also increase the risk for heart disease. The thyroid hormones affect heart rate and the how much blood is pumped by the heart. Hypothyroidism also increases the risk for higher levels of “bad” cholesterol, triglycerides, and other fats related to heart disease. In addition, pericardial effusion (fluid around the heart) and congestive heart failure (inability of the heart to pump blood forward) are possible heart conditions that might develop with severe hypothyroidism. 
Other potential problems may include high blood pressure, heart enlargement, increased strain on the heart and stiffness of blood vessel walls, as well as a low heart rate. 
To lower the risk of heart-related problems due to hypothyroidism, it's important to schedule routine checkups and monitor your blood pressure, as well as your cholesterol levels. 
If left untreated, problems can occur from heart disease. This may include:
  • Congestive heart failure
  • Heart attack
  • Stroke
  • Peripheral artery disease
  • Sudden cardiac arrest
Heart-related problems due to hypothyroidism can be treated. It's important to make regular appointments with your doctors to check your blood pressure and cholesterol levels. You may also consider asking your doctor if medication to treat heart problems is needed. 

How is hypothyroidism diagnosed?

Blood tests can measure your levels of thyroid-stimulating hormone (TSH) and thyroid hormone (T4). You have hypothyroidism when you have high TSH and low T4 levels in your blood. In very early or mild hypothyroidism, TSH will be high but T4 may be normal. In this case, your doctor may measure the thyroid levels more frequently to determine if hypothyroidism develops over time. When the cause of hypothyroidism is Hashimoto disease, blood tests can detect anti-thyroid antibodies that attack the thyroid. 

How is hypothyroidism treated?

Hypothyroidism is treated with thyroid hormone medication, taken as a pill. Levothyroxine is the drug of choice. It is a synthetic (laboratory-made) form of T4 that is identical to the T4 the thyroid naturally makes. Levothyroxine comes in brand-name and generic versions. Changing the manufacturer of the medication could alter the amount of medicine your body gets; so preferably, try to consistently take the same dose, made by the same company at all times. Often, this might be resolved by using a branded levothyroxine product.
Most people need thyroid hormone replacement for life. If the brand or dosage needs to be changed, you should have blood tests for TSH done again. Your dose will be adjusted based on your TSH tests. Over time, doses of thyroid hormone that are too high can lead to bone loss, abnormal heart function, and abnormal heart rhythms. Doses that are too low may not relieve your symptoms. Dose adjustment may be necessary over your lifetime, including during pregnancy. You can discuss dose changes during your regular check-ups with your doctor.

How will you know if you should get tested?

If you have one or more of the symptoms of hypothyroidism, or if thyroid disease runs in your family, ask your doctor if you should have a blood test. Doctors may also recommend testing in women over the age of 60, even if they don't have symptoms. If you are diagnosed with hypothyroidism, you will need treatment to avoid serious health problems.

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Questions to ask your doctor

  • Do I have hypothyroidism?
  • What treatment do I need for it?
  • What are the risks and benefits of each of my treatment options?
  • How often should I be retested?
  • Should I see an endocrinologist?
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