Although they have similar-sounding names, hyperthyroidism and hypothyroidism are opposites. What they have in common is that they both describe the levels of thyroid hormones that your thyroid gland produces.
In this article, we'll help you understand the proper function of the thyroid, the role it plays in the body, and how both hyperthyroidism and hypothyroidism prevent it from doing its job effectively.
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The thyroid is a butterfly-shaped gland located in the front of the neck. It produces three hormones that help set the body's resting metabolic rate. The first two hormones — triiodothyronine (T3) and thyroxine (T4) — are the main thyroid hormones. The third, calcitonin, plays a role in calcium metabolism.
As a regulator of metabolism, the thyroid plays an important part in regulating energy. If the body needs more energy, the gland will produce more of its hormones. The thyroid gland doesn't know how to do this on its own. Instead, it relies on another gland, the pituitary gland, to provide that information.
The pituitary gland is a pea-shaped gland located at the base of the brain that produces thyroid-stimulating hormone (TSH), which travels to the thyroid and tells it to produce more T3 and T4.
When increased levels of T3 and T4 are released to boost your body's metabolism, it makes the cells work harder. As a result, they need more energy as well.
To understand some of the symptoms of hyperthyroidism and hypothyroidism a little better, let's look at a few things that happen¹ when the thyroid boosts cell activity. These include the following:
An increase in body temperature
Increased heart rate
Faster utilization of food
As a regulator of the body's basal metabolic rate, the thyroid has quite a balancing act to play. If it produces too many hormones, the metabolism will be too high. Too few hormones and the metabolism is too low. This is what exactly happens with hyperthyroidism and hypothyroidism.
These conditions are also known as overactive thyroid (hyperthyroidism) and underactive thyroid (hypothyroidism). Hyperthyroidism means your thyroid produces too many hormones, and hypothyroidism is the opposite.
Symptoms of hypothyroidism and hyperthyroidism also differ due to their opposite conditions. As you look at the list of symptoms below, refer to the effects of increased thyroid hormone production on the body. This will help you understand some of the symptoms that too much or too little hormones can cause.
Hyperthyroidism symptoms vary from person to person. Some of the more common symptoms that those with overactive thyroid experience are listed below, though it's unlikely that an individual will experience all of them.
Intolerance to heat or unusual sweating
An increase in heart rate or an irregular heartbeat
Muscle weakness or shakiness
Increased bowel movement frequency
Nervousness or irritability
Older people may also experience some symptoms that younger ones don't, like decreased appetite.
The symptoms of hypothyroidism will also be different from person to person. You can see here that the first few conditions are merely the opposite of those experiences with hyperthyroidism.
Intolerance to cold
Decreased heart rate
Unexplained weight gain
Pain in the joints or muscles
Irregular menstrual periods
Maintaining the proper balance of thyroid hormones requires a delicate balancing act. Several medical conditions affect the thyroid in a way that unnaturally increases or decreases its production.
The most common causes of hyperthyroidism are listed below:
Graves disease - This autoimmune disorder attacks the thyroid gland, causing it to produce too much hormone.
Overactive thyroid nodules - These are lumps on the thyroid most often found in older adults. These are relatively common but should be further evaluated with testing by your doctor and may cause the thyroid to overproduce hormones.
Thyroiditis - If the thyroid becomes inflamed, it can cause thyroid hormone to leak into the bloodstream.
Iodine - This chemical is a key component in thyroid hormone production. Consuming too much iodine can result in your thyroid becoming overactive.
Some of the causes of hyperthyroidism have an equivalent that can lead to the opposite condition. Below is a list of common causes for hypothyroidism.
Hashimoto's disease - This autoimmune disorder has the opposite effect of Grave's disease. It weakens the thyroid until it cannot produce enough hormones.
Thyroiditis - Just as some forms of thyroid inflammation can cause it to over-produce hormones, some can cause underproduction.
Congenital hypothyroidism - This is a condition that some babies have at birth. It occurs when the thyroid isn't fully developed or doesn't work properly.
Medications - Certain medications for heart problems, bipolar disorder, or cancer treatment can interfere with your body's thyroid hormone production and cause hypothyroidism.
Both hyperthyroidism and hypothyroidism can be diagnosed by measuring the thyroid hormones levels in your blood, including TSH, T3, and T4 levels. Based on these results, your doctor may recommend further bloodwork and imaging tests based on these results.
Treatment for both thyroid conditions focuses on bringing the thyroid hormone levels back to where they are supposed to be.
Hyperthyroidism mainly involves using oral medication, radioactive iodine therapy, or surgery on the thyroid gland.
On the other hand, hypothyroidism is commonly treated with levothyroxine, a medication that replaces the missing thyroid hormone.
Keeping your body's metabolic rate at the ideal level requires healthy thyroid function. A variety of causes can result in your thyroid gland producing too much or too few of the hormones that regulate your metabolic rate.
If you experience any of the symptoms of an over-or underactive thyroid, consult with a doctor so that they can narrow down the cause and get you started on treatment.