Underactive thyroid
An underactive thyroid (hypothyroidism) is when your thyroid gland doesn't produce enough of the hormone thyroxine (also calledT4).
Most cases of an underactive thyroid are caused by the immune system attacking the thyroid gland and damaging it, or by damage that occurs as a result oftreatments for Thyroid cancer or an overactive thyroid .
An underactive thyroid often occurs when the immune system, which usually fights infection, attacks the thyroid gland. This damages the thyroid, which means it's not able to make enough of the hormone thyroxine,leading to the symptoms of an underactive thyroid .
A condition called Hashimoto's disease is the most common type of autoimmune reactionthatcauses an underactive thyroid.
It's not clear what causes Hashimotos disease, but it runs in families. It's also common in people with another immune system disorder, such as type 1 diabetes and vitiligo .
An underactive thyroid can also occur as a side effect or complication of previous treatment to the thyroid gland, such as surgery or a treatment called radioactive iodine therapy.
These treatments are sometimes used for an overactive thyroid(where the thyroid glandproduces too much hormone) or thyroid cancer.
Worldwide,alack of dietaryiodine is a common cause of an underactive thyroid, because the body needs iodine to make thyroxine. However, iodine deficiency isuncommon in the UK.
Babies are sometimes born with an underactive thyroid because the thyroid gland doesn't develop properly in the womb. This is called congenital hypothyroidism and isuncommon, affecting around 1 in 3,000 babies. It'susually picked up during routine screening soon after birth.
The Great Ormond Street Hospital for Children website has more information about congenital hypothyroidism and how it's treated .
A problem with the pituitary gland could lead to an underactive thyroid.The pituitary gland sits at the base of the brain andregulates the thyroid. Therefore, damage to the pituitary gland may lead to an underactive thyroid.
An underactive thyroid has also been linked tosome viral infections or somemedications used to treat other conditions, such as:
Speak to your GP or specialist if you're concerned that a medication you're taking may be affecting your thyroid hormone levels.
An underactive thyroid gland (hypothyroidism) is where your thyroid gland doesn't produce enough hormones.
Read more about the symptoms of an underactive thyroid (hypothyroidism), including tiredness, weight gain, depression and increased sensitivity to cold.
Read about the causes of an underactive thyroid (hypothyroidism), including the immune system attacking the thyroid gland and previous thyroid treatment.
Read about the importance of correctly diagnosing an underactive thyroid (hypothyroidism) using a specialised type of blood test called a thyroid function test.
Read about how an underactive thyroid (hypothyroidism) is treated. The first line treatment is a daily hormone replacement tablet called levothyroxine.
Read about the complications of an untreated underactive thyroid, including heart problems, goitre and pregnancy-related complications.