The liver is the body's clearinghouse for toxins and waste products and an important synthesizer for many of the body's proteins and fats. Decreased liver function may occur slowly over time, with few symptoms until severe damage is done, or can be acute, destroying the liver almost overnight. Decreased liver function from any cause can lead to cirrhosis, destruction of the liver tissue and replacement with fibrotic tissue.
Viral Infections
Any viral infection that causes inflammation of the liver is called viral hepatitis. Hepatitis can be acute or chronic. Some forms of hepatitis, such as hepatitis A and E, are acquired through the fecal-oral route, while others are blood borne. Hepatitis A is a onetime infection that normally has no lasting effects, although you may be quite ill for several weeks. Hepatitis B and C are lifelong infections that cause serious liver damage over time. Hepatitis C is currently the most common reason for liver transplantation in the United States today. Epstein-Barr virus and cytomegalovirus can cause acute liver failure.
Alcohol Abuse
Alcohol damages the liver in stages, beginning with enlargement known as fatty liver, then progressing through inflammation of the liver, alcoholic hepatitis and finally to fibrosis of the liver, or cirrhosis, which leaves very little functioning tissue.
Congenital Diseases
Many congenital diseases can damage the liver. Galactosemia, thalassemia, Wilson's disease and biliary atresia are all diseases that can cause liver damage in children. In adults, hematochromatosis, primary sclerosing cholangitis, sarcoidosis and cystic liver disease are diseases that all damage the liver over time.
Medications and Toxins
Some medications, such as Tylenol, or acetaminophen, can seriously damage the liver if taken in excess. Acetaminophen overdose is the most common cause of acute liver failure in the United States, according to the Mayo Clinic. Children taking acetaminophen during a viral infection may develop Reye's syndrome, which causes acute liver failure. Products such as herbs, which are less regulated, can also result in decreased liver function. Herbs known to cause liver damage if taken to excess include comfrey tea, chapparel, kava and yohimbe, the American College of Gastroenterology reports. Ephedra and pennyroyal can also cause acute liver damage.
Vitamins and supplements that can damage the liver include iron and Vitamin A. Statins, cholesterol lowering medications, can also cause a decrease in liver function. Poisonous mushrooms can cause acute liver failure. The wild mushroom Amanita phalloides may be mistaken for an edible mushroom, the Mayo Clinic reports.
Cancer
Cancer of the liver can be primary, meaning that the cancer started in the liver; or secondary, meaning that it started in a different part of the body and spread, or metastasized, to the liver. Early liver cancer may have no symptoms, but as time goes on, signs of decreased liver function such as jaundice, weight loss, weakness and fluid retention appear. Small primary cancers can be removed, while multiple tumors or metastasized tumors are harder to treat and cause more damage to the liver.
Vascular Diseases
Diseases that block the veins to the liver can cause acute liver failure. Portal vein thrombosis, Budd-Chiari syndrome and venoocclusive disease are examples of vascular disease.
