Hyperthyroidism & Cholesterol

The thyroid gland located in your neck produces two important hormones known as triiodothyronine, commonly called T3 and thyroxine, known as T4. These two hormones circulate throughout the body and regulate the function of most tissues and organs, including the regulation of cholesterol. High blood cholesterol causes atherosclerosis, which leads to heart disease -- the leading cause of death in the United States. Patients who suffer from hyperthyroidism usually have low blood cholesterol levels, which leads scientists to study the effects of thyroid hormone on reverse cholesterol transport as a possible route of treatment.

Hyperthyroidism

Hyperthyroidism describes a medical condition that occurs when the thyroid gland produces too much thyroid hormone. The increase in thyroid hormone causes your metabolism to increase, which causes symptoms that include heart palpitations, increased heart rate, nervousness, breathlessness, insomnia, muscle weakness, fatigue, weight loss and increased bowel movements. Inflammation of the thyroid, a condition called thyroiditis, can cause hyperthyroidism. Graves' disease, a condition that occurs when the immune system creates antibodies against the thyroid gland, also causes hyperthyroidism. The increase in thyroid hormone stimulates the body to use more blood cholesterol to produce bile acids.

Thyroid Hormone and Cholesterol

Your liver plays a vital role in the production, regulation and excretion of cholesterol. Liver cells produce about 75 percent of your total blood cholesterol. The liver also produces the specialized proteins needed to transport cholesterol through the blood, including low-density lipoprotein, or LDL, and high-density lipoprotein, or HDL. Cells within the liver contain specialized LDL receptors that bind to cholesterol returned to the liver through the reverse cholesterol transport. The cells need the protein known as sterol regulatory element-binding protein to activate the receptors and thyroid hormones that regulate the expression of this protein. The more thyroid hormone and protein, the more receptors bind to cholesterol, which results in more cholesterol being removed from the blood.

Reverse Cholesterol Transport

LDL binds to cholesterol in the liver and carries it through the bloodstream to deliver to the cells throughout the body. When there is too much cholesterol for the cells to use, the LDL remains in the blood vessels. HDL picks up excess cholesterol from the tissues. HDL also can remove excess cholesterol from the blood vessels. An enzyme in the HDL molecule transfers the cholesterol to LDL and sends it through the reverse cholesterol transport back to the liver. Once in the liver, this LDL binds to the LDL receptors and the liver cells use the cholesterol to produce bile acids, which eventually get excreted from the body.

Thyroid Hormone as Treatment

Scientists, knowing that high levels of thyroid hormone help reduce cholesterol levels, were prompted to study whether thyroid hormones can be used as a treatment for high cholesterol levels. Although no specific studies have been conducted in humans, findings published in the December 2010 issue of the "World Journal of Gastroenterology" caution that although studies in the rat model show promise, rats metabolize cholesterol differently. In addition, thyroid hormone may cause a decreased level of HDL, which also increases the risk for heart disease. This study suggests further research be conducted in humans to determine the effectiveness of thyroid hormones in treating high blood cholesterol.

Hyperthyroidism & Cholesterol