What Causes Hyperthyroidism?

Hyperthyroidism is a condition in which your thyroid gland produces more hormones than your body needs.

Your thyroid gland is on the front side of your throat, near your windpipe (trachea). Your thyroid makes two hormones that control metabolism: triiodothyronine (T3) and thyroxine (T4).

Metabolism refers to multiple processes your body goes through to change chemicals from one thing to another—for example, changing food to energy.

Your entire body is affected by thyroid hormones. Excessive thyroid hormone production will speed up functions like your heart rate and digestion. It can also make sleeping difficult and cause unpleasant symptoms like mood swings and irritability.

Hyperthyroidism is generally treatable, particularly after determining the underlying cause. Keep reading to learn about both the common and relatively rare causes of hyperthyroidism.

Signs and symptoms of hyperthyroidism

Speak to a healthcare professional if you have symptoms of hyperthyroidism, including:

• Increased or irregular heart rate

• Losing weight despite an increased appetite

• Feeling thirstier than usual

• More frequent urination or diarrhea

• Trouble sleeping, restlessness, fatigue, and anxiety

• Changes in your menstrual cycle

• Bulging eyes

• Tremor of hands

• Increased body temperature

• Change in the texture of your hair

• Enlarged thyroid gland resulting in swelling of the neck (goiter)

Common causes of hyperthyroidism

Graves' disease

80% of diagnosed hyperthyroidism¹ is due to Graves’ disease, making it the most common cause of overactive thyroid. Graves' disease is an autoimmune disorder in which the immune system attacks the thyroid gland causing it to overproduce hormones.

Researchers have yet to determine the cause of Graves' disease. However, it is genetic, so your risk of hyperthyroidism is higher if you have a family history of Graves’ disease.

Graves' disease affects mainly females between the ages of 20-40², but it can develop in females or males of any age.

Thyroiditis

Another common cause of hyperthyroidism is thyroiditis, an inflammation of the thyroid gland that causes thyroid hormones to leak into your bloodstream. It raises your amount of thyroid hormones above normal levels. 

Three types of thyroid inflammation can lead to hyperthyroidism:

Subacute thyroiditis(“Subacute” is a term for a condition somewhere between acute and chronic). This form of thyroiditis causes a tender, painful, swollen, and inflamed thyroid gland. It may cause difficulties swallowing food, fever, and fatigue.

Postpartum thyroiditisA mild thyroid inflammation that occurs after giving birth.

Painless, aka “silent” thyroiditisThis type of thyroiditis is an immune reaction that causes painless swelling and inflammation of the thyroid gland. Pregnancy and chemotherapy are two known causes. 

Excessive iodine consumption

Certain foods are high in iodine, such as seafood, seaweed, and dairy. Your body doesn’t make iodine, so some amount in your diet is necessary. However, if you consume too much, your thyroid will produce excess thyroid hormones leading to hyperthyroidism.

Also, x-ray dye (contrast) contains high levels of iodine which could contribute to overactive thyroid. 

Overactive thyroid nodules

Thyroid nodules are growths on your thyroid. The nodules are benign (non-cancerous) but may cause your thyroid gland to make too much thyroid hormone. Having thyroid nodules increases with age, and it’s possible to have them for many years before they start producing excess thyroid hormones.³

Too much thyroid hormone medication

You may develop hypothyroidism (underactive thyroid) if your thyroid makes too few hormones. This is usually treated with daily synthetic thyroid hormone replacement.

If the prescribed dosage is too high, it can cause unwanted excess thyroid hormone, leading to hyperthyroidism.

Speak to your doctor if you have any concerns or questions about determining or changing dosages.

Rarer causes of hyperthyroidism

Several less common causes of hyperthyroidism include:

• High levels of chorionic gonadotropin — a hormone relevant to maintaining pregnancy in females and sperm production in males),⁴ ⁵

• Pituitary adenoma — a non-cancerous pituitary gland tumor influencing the hormones produced by your thyroid gland

• Thyroid cancer — a less common type of cancer that develops in your thyroid gland, affecting the production of thyroid hormones

What are the risk factors for hyperthyroidism?

Anyone can get hyperthyroidism. However, you are more at risk if you:

• Are female

• Have a history of hyperthyroidism in your family

• Are age 50 or older 

• Are pregnant or went through childbirth in the last six months

• Have an autoimmune disorder

• Are consuming food, supplements, or medication with large amounts of iodine

Complications of hyperthyroidism

When hyperthyroidism remains untreated, it can result in serious health complications. These include:

Graves' Ophthalmology

Graves' ophthalmology causes an elevated risk for vision loss.⁶ Therefore, it's crucial to seek medical attention when you notice any eye problems. Your health care provider can then refer you to an ophthalmologist (eye specialist) to help manage and treat your symptoms.

Some of the eye-related symptoms of this condition include:

• Eyeball protrusion

• Eyelid retraction

• Blurred or double vision

• Watering eyes

Some risk factors may increase your chances of getting Graves' ophthalmology, including:

• Smoking 

• How long you have had Graves' hyperthyroidism (the longer you have the condition, the higher the chances of getting Graves' ophthalmology)

Treatment for this condition depends on the severity and may include prescription eye drops, steroid medications, or surgery.

Thyroid storm

A thyroid storm is a life-threatening condition that can result from untreated hyperthyroidism and should be treated as a medical emergency.

It causes body temperature, heart rate, and blood pressure all to become dangerously high, hence “storm.”

Call 911 immediately if you suspect that you or someone you care about are experiencing symptoms, such as:

• Loss of consciousness

• High fever (100–106℉)

• Heart rate may be as high as ​​200 beats per minute (BPM) 

• High blood pressure

• Severe agitation or confusion

• Jaundice (yellow discoloring of skin or whites of eyes)

• Diarrhea, vomiting, or nausea

Causes may also include having a heart attack, abruptly stopping your anti-thyroid medication, injuring your throat, or complications from diabetes.

Diagnosing hyperthyroidism

Symptoms of hyperthyroidism may seem similar to many other medical conditions.

So, your doctor will usually start screening for hyperthyroidism by ordering bloodwork to check your thyroid-stimulating hormone (TSH) levels. TSH is created in the brain and goes to the thyroid gland to increase hormone production and release.

A high TSH blood level means your body isn't producing enough thyroid hormone.  A low TSH level suggests that your body has more thyroid hormone than it needs and may indicate hyperthyroidism. Your doctor may direct you to a specialist (endocrinologist) for further evaluation and treatment.

Treatment of hyperthyroidism

Anti-thyroid medication

Anti-thyroid medicine targets the thyroid gland and blocks the production of hormones. Beta-blockers may help reduce symptoms and bring thyroid hormone levels closer to normal.

Anti-thyroid medication can have some side effects, including:

• Itching

• Skin rashes

• Abnormal hair loss

• Joint and muscle aches

• Fever

• Nausea

• Heartburn

Radioactive iodine treatment

Radioactive iodine treatment involves ingesting a tiny amount of radioactive iodine in a capsule or liquid form.

The thyroid gland takes up the medicine, and the drug permanently destroys part of the entire gland, ceasing the production of the hormone in your body. This treatment option may be appropriate if there has been a severe reaction to an anti-thyroid medication or if your body isn’t responding well to the medication. However, radioactive iodine treatment is unsuitable for pregnant women or children. 

Surgery

Surgery for hyperthyroidism is known as a thyroidectomy. It involves the removal of your entire thyroid gland (or part of it). Surgery is usually the last resort when other non-invasive treatments have failed. With thyroidectomy, you will take thyroid hormones for the rest of your life to prevent the effects of low thyroid hormone levels in your body.

Surgery is the preferred treatment option for patients with Graves' disease, and it has the lowest hyperthyroidism relapse rate compared to the other treatment options.⁷

When to speak with your doctor 

If you're undergoing treatment for hyperthyroidism, you should seek urgent medical attention if you experience the following symptoms:

• Your heart rate is abnormally high

• Your blood pleasure is unusually low or high

• A sudden feeling of anxiety or difficulty breathing

• Feeling weak and sleepy

• Continuous vomiting or having diarrhea 

• Body temperatures are usually high or low

• Extreme irritability

The lowdown

Hyperthyroidism (overactive thyroid) tends to be caused by Graves' disease, thyroiditis, consuming large amounts of iodine, thyroid nodules, or taking too high a dose of thyroid hormone medication.

More rarely, hyperthyroidism may be caused by cancer, pituitary gland problems, or elevated levels of chorionic gonadotropin.

Hyperthyroidism causes symptoms like increased or irregular heart rate, weight loss, extreme thirst, swelling of the neck, trembling hands, and fever. Hyperthyroidism is manageable and treatable. Appropriate treatment will depend on the individual but typically involves medication, radioactive iodine treatment, or surgery.

Unmanaged hyperthyroidism can result in Graves' ophthalmology, thyroid storm, pregnancy complications, osteoporosis, or heart failure.

If you suspect that you may have hyperthyroidism or are already diagnosed but have concerns about your condition, speak with a qualified medical professional as soon as possible.