Overview
The thyroid is a small, butterfly shaped gland in the front of the neck. The hormones it makes set the pace at which the body works, affecting the heart, digestion, temperature, weight and mood.
In an underactive thyroid, also called hypothyroidism, the gland does not make enough of these hormones. Because the change is slow, symptoms may take months or years to be noticed, and are easily put down to age or stress.
Symptoms
Symptoms vary from person to person and often overlap with other conditions. Common ones are:
- Tiredness and low energy
- Feeling cold when others do not
- Weight gain
- Constipation
- Dry skin, brittle nails and thinning hair
- Puffiness of the face
- Low mood and difficulty concentrating
- A hoarse voice
- Heavy or irregular periods, and difficulty conceiving
- A slow heartbeat
When to see a doctor
Otherwise, see a doctor if you have the symptoms above, if there is a swelling in the front of the neck, or if thyroid disease runs in your family. Tell your doctor if you are pregnant or planning a pregnancy, as the dose usually needs reviewing.
Causes
The most common cause is an autoimmune condition, Hashimoto's disease, in which the immune system slowly damages the thyroid. Other causes include surgery to remove part or all of the thyroid, treatment for an overactive thyroid, radiation to the neck, and certain medicines such as lithium and amiodarone.
Inflammation of the gland, called thyroiditis, can cause it, and sometimes it is present from birth. Lack of iodine is an important cause worldwide, although it is uncommon where salt is iodised.
Risk factors
- Being a woman
- Being over 60
- A family history of thyroid disease
- A previous thyroid problem, thyroid surgery or radiation to the neck
- Recent pregnancy
- Other autoimmune conditions, such as type 1 diabetes, coeliac disease, rheumatoid arthritis or lupus
Complications
Left untreated, an underactive thyroid can lead to:
- Raised
- Heart problems, including coronary heart disease and heart failure
- Weakening of the bones
- Problems in pregnancy, including high , birth defects, premature birth and miscarriage
- Myxoedema coma, a rare but life threatening emergency
Prevention
An underactive thyroid usually cannot be prevented, because the common causes are autoimmune. Using iodised salt avoids iodine deficiency, but taking iodine supplements without medical advice is not helpful and can cause problems.
What can be done is to find it early. Ask about a thyroid blood test if you have had thyroid surgery or treatment for an overactive thyroid, or if thyroid disease runs in the family.
Diagnosis
A doctor will ask about symptoms and family history and feel the neck to check whether the gland is swollen. Blood tests measure thyroid stimulating hormone () and thyroxine (T4). A high TSH with a low thyroxine points to an underactive thyroid. Antibody tests can show whether the cause is autoimmune.
Treatment
Treatment is levothyroxine, a tablet that replaces the hormone the thyroid can no longer make. It is usually taken once a day on an empty stomach, because food, and supplements such as calcium and iron, can stop it being absorbed properly.
A blood test is repeated a few weeks after starting or changing the dose, then less often once the level is steady. Most people need the tablet for life and feel considerably better once the dose is right. Tell any doctor treating you that you take it.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“Once I feel better I can stop the tablets.”What is true?
Fact
The tablet replaces a hormone the thyroid can no longer make, so feeling well usually means the dose is right, not that the problem has gone. Stopping lets the symptoms return. Never stop or change the dose without speaking to your doctor first.
Myth“Eating more iodine, or taking an iodine supplement, will fix an underactive thyroid.”What is true?
Fact
The thyroid does need iodine to make its hormones, but where salt is iodised, lack of iodine is rarely the cause. The commonest cause here is the immune system attacking the thyroid, and extra iodine does not treat that. People with autoimmune thyroid disease are often advised to limit high iodine foods and supplements.
Myth“All my weight gain is because of my thyroid, and the tablets will make the weight fall off.”What is true?
Fact
Weight gain is one of many symptoms, and most people gain only a modest amount. Replacing the hormone usually improves tiredness, constipation and dry skin, and can help with some of the weight, but eating patterns and activity still matter.
Myth“Thyroid medicine is a strong hormone, so it must be harmful to take for years.”What is true?
Fact
Levothyroxine is the same hormone the thyroid itself makes, given in the amount the body is missing. When the dose is correct it causes no side effects. Too much can cause problems such as sleeplessness, headaches or loose motions, which is why the dose is checked with blood tests.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
Will I have to take the tablet for the rest of my life?
Usually yes, because the thyroid does not recover in most cases. A few causes, such as inflammation after a viral illness or after pregnancy, can settle on their own. Your doctor will decide based on repeat blood tests.
Does an underactive thyroid affect pregnancy?
It can. If it is not treated, it raises the chance of high blood pressure in pregnancy, premature birth and miscarriage. With treatment and regular blood tests most pregnancies go well, so tell your doctor as soon as you are planning or expecting a baby.
I feel tired all the time. Should I get my thyroid checked?
Tiredness has many causes, and most people who feel tired do not have a thyroid problem. A blood test is a reasonable step if tiredness comes with other symptoms such as feeling cold, weight gain, constipation or dry skin, or if thyroid disease runs in the family.
