Cholesterol is a waxy fat-like substance your body uses to add structure to cell membranes, produce hormones and make bile acids important for the digestion of fats. Although your body needs cholesterol, too much cholesterol increases your risk for heart disease. The National Heart Lung and Blood Institute defines high cholesterol as a total cholesterol of 240 mg/dL or higher or a low-density lipoprotein, LDL, cholesterol of 160 mg/dL or higher. The liver and the small intestine play vital roles in the production and regulation of cholesterol, so disorders of these organs may lead to high cholesterol.
Functions
Although doctors stress the important of a low-fat, low-cholesterol diet to maintain healthy cholesterol levels, your liver actually produces about 75 percent of your total cholesterol. The liver also produces the specialized proteins, known as lipoproteins, needed to transport cholesterol. Low-density lipoprotein, LDL, functions to carry cholesterol from the liver through the blood vessels to the cells. High-density lipoprotein, HDL, functions to pick up cholesterol from the tissues and blood vessels and carry it back to the liver. The liver then uses this cholesterol to produce bile acids. The bile acids travel from the liver to the gallbladder for storage. When foods reach your small intestine, the gallbladder releases bile acids to the small intestine where they break down fats into small droplets. The cells lining the small intestine absorb the fats and cholesterol, which then contribute to your total blood cholesterol levels. Disorders of the small intestine that inhibit the absorption of nutrients, like celiac disease, may help to lower cholesterol levels.
Primary Biliary Cirrhosis
Primary biliary cirrhosis is a chronic liver disorder that occurs when the immune cells of the body mistakenly attack the cells of the bile ducts, causing inflammation. Bile produced by the liver travels through the bile ducts to the gallbladder and then to the small intestine. When these ducts become inflamed, bile builds up in the liver, causing inflammation of the liver that can lead to liver damage and, over time, the buildup of scar tissue known as cirrhosis. The scar tissue in the liver interferes with the flow of blood through the liver and impairs liver functions like removing toxins from the blood, processing vitamins and nutrients, making proteins and producing bile. Because the production of bile acids is the body's main mechanism for removing cholesterol from the body, a reduction in bile acid production causes high blood cholesterol levels, according to the National Digestive Diseases Information Clearinghouse.
Nonalcoholic Steatohepatitis
Nonalcoholic steatohepatitis, often referred to as NASH, is a liver disorder that resembles alcoholic liver disease but occurs in those who drink little or no alcohol. The characteristic features of NASH include fat in the liver and inflammation that can cause damage to the liver cells. The National Digestive Diseases Information Clearinghouse reports that approximately 2 to 5 percent of Americans suffer from NASH, but that most do not realize they have the disease, making it known as a silent liver disease. Over time NASH causes scar tissue to develop in the liver that can lead to cirrhosis, which inhibits liver function. Like primary biliary cirrhosis, when the liver cannot function properly, it fails to produce bile acids and causes high blood cholesterol levels.
Diabetes
Although classified as an endocrine disorder, diabetes affects your whole body, including liver function. Diabetes, characterized by the inability to process glucose in the blood, can contribute to liver diseases, including NASH and biliary diseases. These diseases increase your blood cholesterol levels. In addition, diabetes also affects your cholesterol levels. Diabetics can develop diabetic dyslipidemia, a condition characterized by high levels of LDL, or "bad" cholesterol, and low levels of HDL, or "good" cholesterol, according to the American Heart Association. The effects on cholesterol levels, along with the damage it causes to other tissues like blood vessels, makes diabetes a major risk factor for heart disease.
References
- National Heart Lung and Blood Institute: How is High Blood Cholesterol Diagnosed?; September 2008
- National Digestive Diseases Information Clearinghouse: Nonalcoholic Steatohepatitis; November 2006
- National Digestive Diseases Information Clearinghouse: Primary Biliary Cirrhosis; December 2008
- "Clinical Diabetes"; Liver Disease and Diabetes; G. Levinthal, et al.; 1999
- American Heart Association: Cholesterol Abnormalities and Diabetes; September 2010
