Hashimoto's disease is the most common cause of hypothyroidism in the United States, according to the National Endocrine and Metabolic Diseases Information Service. Hashimoto's disease occurs when the cells of your immune system attack the cells of the thyroid gland, a butterfly-shaped gland in the neck. The thyroid gland produces hormones that regulate all metabolic processes in your body, including the production and excretion of cholesterol.
What is Cholesterol?
Your body needs cholesterol, a molecule classified as a lipid, to trigger the production of hormones and to provide structure to cell membranes. The majority of what you hear about cholesterol focuses on reducing your intake of dietary cholesterol, but in reality, your diet, including dietary cholesterol and fats, contributes only about 25 percent of your total cholesterol level. Your body, mostly the cells in your liver, produces approximately 75 percent of all your cholesterol.
Role of Your Liver
Your liver plays a major role in the production, regulation and excretion of cholesterol. During a complex series of biochemical reactions, your liver converts fatty acids into cholesterol. The enzyme HMG CoA reductase promotes the production of cholesterol while the enzyme HMGR regulates cholesterol production. As your blood cholesterol levels increase, the production of HMGR decreases, which lowers the production of cholesterol. Liver cells also contain specialized LDL cholesterol receptors, which attract and bind the cholesterol it needs to produce bile acids. Thyroid hormone regulates the expression of sterol regulatory element-binding protein, which activates the LDL receptors.
Role of Thyroid Hormone
Your thyroid gland produces two main hormones known as triiodothyronine -- T3 and thyroxine -- T4. These hormones regulate nearly all tissues and functions throughout the body, including breathing, heart rate, temperature, muscle strength, moisture level, menstrual cycles, weight and cholesterol levels. A low level of thyroid hormone, such as occurs in people with Hashimoto's disease, inhibits the sterol-regulatory binding protein, which reduces the number of LDL receptors in the liver. That causes more cholesterol to remain in the blood.
Treatment
Treating high cholesterol levels requires treating any underlying causes for the high cholesterol. In the case of patients with Hashimoto's, you must first treat the disease and then try to reduce your cholesterol levels. When Hashimoto's disease damages the thyroid gland enough to cause hypothyroidism, your doctor can prescribe synthetic thyroid hormone to replace the lost hormones. The synthetic thyroid hormones can stimulate the production of sterol regulatory element-binding protein. That activates the LDL cholesterol receptors in the liver to bind more LDL cholesterol, therefore reducing the blood cholesterol level.
References
- National Endocrine and Metabolic Diseases Information Service: Hashimoto's Disease; May 2009
- "Journal of Biological Chemistry"; Thyroid Hormone Regulation and Cholesterol Metabolism; Shin and Osborne; 2008
- The Medical Biochemistry Page: Introduction to Cholesterol Metabolism; April 2011
- Colorado States University: Secretion of Bile and the Role of Bile Acids in Digestion; November 2001
- American Heart Association: About Cholesterol; May 2011
