Cholesterol is an essential nutrient for the body because it is a crucial component of cell membranes and a precursor for steroid hormones, vitamin D assimilation and bile acids. Bile acids are excreted from the gallbladder in order to digest dietary fat. Gallstones form when the bile produced in the liver is abnormally high in cholesterol, which crystallize into small stones, although high blood cholesterol is not a major factor. Gallstones are classified according to composition and they can lead to a variety of symptoms, some of which require medical attention.
Incidence of Gallstones
According to "Professional Guide to Diseases," about 20 million Americans have developed gallstones for a variety of reasons, although less than 3 percent will complain to a doctor about symptoms and only half of these cases will experience recurrent symptoms. Women are much more likely to develop gallstones, with about 24 percent having them by the age of 60 in the United States. Women are thought to have a higher incidents because estrogen stimulates the liver to remove more cholesterol from the bloodstream and use it in bile production. About 12 percent of American men have gallstones by the age of 60, although the vast majority of them are asymptomatic.
Symptoms of Gallstones
Symptoms caused by gallstones depend mainly on where the stones become lodged and how big they grow. Stones can block the cystic duct, common bile duct, pancreatic duct or the ampulla of Vater. According to "Human Biochemistry and Disease," blockage of most ducts can lead to acute cholecystitis, an inflammatory condition characterized by retention of bile in the gallbladder, severe pain abdominal, vomiting, nausea, bloating, burping and sometimes secondary infection by E. coli bacteria. Gallstone "attacks" are often precipitated by ingestion of fatty foods. Gallstones that block other parts of the biliary tract can lead to serious medicial emergencies, such as ascending cholangitis or pancreatitis.
Types of Gallstones
Gallstone formation is not considered a normal consequence of aging, nor is it considered a disease, unless it leads to infection or overt symptoms. Gallstones vary in size from sand-like to as large as a golf ball. On the basis of composition, gallstones can be divided into cholesterol stones, pigment stones and mixed stones. According to "Biochemical, Physiological and Molecular Aspects of Human Nutrition," cholesterol stones are the most common and are comprised of at least 80 percent cholesterol, varying in color from light yellow to dark brownish-green. Other components include calcium carbonate, palmitate and biliruben. Pigment stones are usually small and contain much more bilirubin, bile pigments and calcium salts from the bile acids and less than 20 percent cholesterol by weight. Mixed stones can contain between 20 and 80 percent cholesterol and a mixture of the other components.
Cholesterol and Gallstones
Although gallstones are often formed from over-saturation of cholesterol in the bile, high blood cholesterol levels in the blood are not directly associated with gallstones. However, according to "Biochemistry of Human Nutrition," gallstone formation is associated with low HDL cholesterol levels, the "good" cholesterol, and high triglyceride levels, which seem to impair emptying actions of the gallbladder (Reference 4). Lack of bile salts is a much more common cause of gallstones because they are needed to solubilize the cholesterol and keep it from precipitating out of solution. Causes for decreased supply of bile acids include poor absorption of bile in the intestines, blockages in the bile's passageway, severe liver disease, suppression of bile acid production and use of certain medications. Some drugs, classified as fibrates, increase the risk for gallstone formation by increasing the amount of cholesterol secreted into the bile from the liver.
References
- "Professional Guide to Diseases: Ninth Edition"; Springhouse Publishing; 2009
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Biochemistry of Human Nutrition"; George Gropper; 2000
