High cholesterol is a risk factor for heart disease and stroke. Dietary and other lifestyle choices can lead to high cholesterol, but sometimes medical conditions, such as a thyroid disorder, may be involved.

Producing too many or too few thyroid hormones can increase the risk of unusual blood cholesterol levels.

This article takes a closer look at the link between the thyroid and cholesterol. It also discusses some of the ways to manage cholesterol and thyroid conditions.

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The thyroid gland is located in the neck, and it produces specific hormones. The two main hormones it produces are triiodothyronine (T3) and thyroxine (T4).

These hormones enter the bloodstream and have uses throughout the body. T3 is the active form of thyroid hormone, and the body utilizes it in its original state. Bodily enzymes can also convert T4 into active T3.

Thyroid hormones play a role in regulating:

  • brain development in children
  • body temperature
  • metabolism
  • growth and development
  • the function of the heart, brain, muscle, and other organs

The pituitary gland secretes thyroid-stimulating hormone (TSH) to stimulate the thyroid to produce hormones. The thyroid gland also produces a hormone called calcitonin.

Thyroid problems

When the thyroid does not produce enough thyroid hormones, it is underactive. This is known as hypothyroidism. On the other hand, producing too many hormones leads to an overactive thyroid. This is called hyperthyroidism.

Almost 5% of people aged 12 years or older in the United States have an underactive thyroid.

An underactive thyroid can cause the following symptoms:

An underactive thyroid can result from an autoimmune condition, such as Hashimoto’s thyroiditis, or due to the surgical removal of the thyroid.

Overactive thyroid is less common. Approximately 1.2% of people in the U.S. have an overactive thyroid.

Symptoms of an overactive thyroid can include:

Several conditions and situations can cause an overactive thyroid. These include the autoimmune condition Graves’ disease, inflammation of the thyroid, and excessive iodine use.

Cholesterol is a waxy substance present in every cell in the body. The body uses cholesterol to make hormones as well as bile acids to help digest fat.

When too much cholesterol builds up in the arteries, it can cause a range of problems, such as heart disease.

Cholesterol travels through the blood by attaching itself to a protein. This bundle of cholesterol and protein is called a lipoprotein.

The principal lipoprotein bundles are high-density lipoprotein (HDL) and low-density lipoprotein (LDL).

HDL is so-called because there is a high cholesterol-to-protein ratio. It is also known as “good” cholesterol because it helps the body get rid of cholesterol from the blood.

LDL features a low cholesterol-to-protein ratio. It is also known as “bad” cholesterol. Higher LDL rates indicate a higher risk of heart disease.

Certain dietary choices may increase the level of LDL cholesterol in the blood. However, high LDL cholesterol may also arise from some medical conditions, including thyroid disorders.

A person’s thyroid function and cholesterol levels are closely linked. Changes in this relationship can result in adverse conditions.

Can an underactive thyroid cause high cholesterol?

Thyroid hormones, primarily T3, play an essential role in helping the liver process and remove excess cholesterol from the body.

When the body does not produce enough thyroid hormones, the liver cannot process as much cholesterol as usual. An underactive thyroid means that the body removes less LDL cholesterol from the blood. This can lead to high levels of LDL and total cholesterol.

According to studies, up to 13% of people with high blood cholesterol also have an underactive thyroid.

Further research has reported inverse links between a person’s thyroid activity and their cholesterol levels. As a result, a person can manage their cholesterol levels with the supplementation of thyroid hormones.

A series of animal studies suggested that elevated TSH, which occurs in hypothyroidism, can potentially lead to increased cholesterol levels.

Can an overactive thyroid cause low cholesterol?

An overactive thyroid can have the opposite effect and cause low levels of cholesterol in the blood. Low cholesterol may lead to adverse health conditions.

However, complications arising from cholesterol levels being too low are less common than those resulting from levels being too high.

Anyone with an underactive or overactive thyroid should contact a doctor for further testing. They should also consult a medical professional if their cholesterol levels are unusual.

The doctor will take a sample of blood to check for levels of TSH and thyroid hormones. The results will show if the thyroid is overactive, underactive, or functioning as expected.

A person may need to fast before a thyroid hormone test, as consuming food can suppress TSH levels significantly, according to some research.

The doctor or laboratory technician may be able to test blood cholesterol levels from the same blood sample. A person may also need to fast before a separate cholesterol level test.

A doctor can recommend a treatment plan to manage both thyroid conditions and unusual cholesterol levels.

Underactive thyroid

People with an underactive thyroid may see improvements in their cholesterol levels if they take a thyroid hormone replacement medication. Doctors commonly prescribe forms of levothyroxine.

When thyroid hormone levels are only slightly below the appropriate level, a doctor may prescribe statins. These are drugs that work to lower cholesterol levels.

Some commonly prescribed statins include:

  • rosuvastatin calcium (Crestor)
  • fluvastatin (Lescol)
  • atorvastatin (Lipitor)
  • lovastatin (Mevacor, Altoprev)
  • pravastatin (Pravachol)
  • simvastatin (Zocor)

Some other treatments for high cholesterol include:

  • losing weight, if applicable
  • getting regular exercise
  • making certain dietary changes, such as reducing saturated fat and increasing fiber intake

Overactive thyroid

People with an overactive thyroid can take medications to reduce thyroid hormone production.

If medications do not work, a doctor may suggest radioactive iodine to shrink the thyroid gland or surgery to remove part of the gland, which will reduce hormone levels.

People who have low cholesterol due to high thyroid hormone levels may see their cholesterol levels increase as a result of treatment.

There is a clear link between thyroid disorders and unusual cholesterol levels.

Those with a new diagnosis of high cholesterol should ask a doctor to check their thyroid hormone levels. Similarly, those who have an underactive thyroid should regularly monitor their blood cholesterol levels and take steps to reduce the risk of developing high cholesterol.

Some people may see results once they treat their thyroid disorder. However, others with high cholesterol levels may need to take cholesterol-lowering medications and make certain lifestyle changes to bring their cholesterol back to appropriate levels.

Read this article in Spanish.