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Can Thyroid Cause High Levels of Cholesterol?

May 12, 2011 | By Stephanie Chandler

The thyroid is a butterfly-shaped gland found in the neck that produces two main hormones, thyroxine -- T4 and triiodothyronine -- T3. These hormones regulate the body's metabolism, the process of converting food into energy. The thyroid affects nearly every cell and tissue in the body including those involved with the production and regulation of cholesterol. If the thyroid fails to produce enough thyroid hormones, a medical condition known as hypothyroidism, it can cause high levels of cholesterol.

Thyroid Hormone Regulation

Other glands in the endocrine system regulate the production and secretion of thyroid hormones. The pituitary gland, found at the base of the brain, secretes the thyroid stimulating hormone, or TSH, to trigger the production of the thyroid hormone. The portion of the brain known as the hypothalamus produces the TSH releasing hormone, known as TRH, that signals the pituitary gland to produce TSH. This cascade of hormones keeps the thyroid functioning to produce just the right amount of the thyroid hormone. When conditions affecting the pituitary gland or hypothalamus inhibit the production of these hormones, the thyroid gland cannot produce enough thyroid hormone to regulate bodily functions like cholesterol levels.

Hypothyroidism

Doctors diagnose patients with low levels of the thyroid hormone with hypothyroidism. Without the proper amount of the thyroid hormone, your metabolism slows down, which means you fail to effectively convert food into energy. This causes a variety of symptoms including fatigue, constipation, depression, unexplained weight gain, muscle weakness and feeling colder than normal. The thyroid hormones play a role in removing excess cholesterol from the body, so when levels decrease your cholesterol levels may increase.

Cholesterol

Cholesterol is a type of fat produced by the cells in the liver. The body uses cholesterol to provide structure to cell membranes and stimulate hormone production. Cholesterol is also vital for the production of bile acids that function to breakdown dietary fat. The liver produces cholesterol and the specialized proteins known as lipoproteins needed to carry cholesterol. Low-density lipoprotein, LDL, carries most of the cholesterol from the liver through the blood vessels to cells in the body. As cholesterol levels increase, the amount of LDL increases in the blood vessels which can contribute to atherosclerosis -- a process of hardening and thickening of the arteries. High-density lipoprotein extracts excess cholesterol from tissues in the body and transfers it to LDL which carries it back to the liver in the process known as reverse cholesterol transport.

Cholesterol Regulation

When the LDL carries cholesterol back to the liver, specialized proteins that function as LDL receptors bind the LDL and convert the cholesterol it carried into bile acids which eventually get excreted from the body. Low levels of thyroid hormone inhibit the sterol regulatory element-binding protein needed to make the LDL receptors. A decrease in this protein means fewer LDL receptors, which means less cholesterol gets converted into bile acids leaving more cholesterol to enter back into the blood vessels. After receiving treatment for hypothyroidism and your thyroid produces more hormones, your high cholesterol levels will decrease.

References

Article reviewed by Avraham Zuroff Last updated on: May 12, 2011

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