After a meal, while watching television, suddenly you feel a stabbing pain below your rib cage. This isn't the first time. Eventually, you find out your pain was caused by gallstones.

Gallstones are a major health problem. About 20 million people in the United States have them and one million new cases are diagnosed each year. "Gallstones are the fifth leading cause of hospitalization," says Dr. Jeffrey Field, professor of internal medicine at the UI College of Medicine and gastroenterologist at UI Hospitals and Clinics.

The gallbladder is a small muscular sac located under the liver that stores bile secreted by the liver. Bile helps you digest fats. At the turn of the century, physicians believed gallstones were always the result of a diseased gallbladder. Today they realize that gallstones, most of which are composed mainly of cholesterol, are primarily caused by a disturbance in cholesterol metabolism within the liver. "There is too much cholesterol relative to the amount of other lipids in the bile," Field says. Cholesterol crystals then form in the bile and grow into larger stones.

Many people can live for years without knowing they have gallstones. Pain below the right rib cage, called biliary colic, is usually the first symptom. "It's a sharp, boring, intense pain that can radiate around to the back. The gallbladder is trying to contract, but the opening into the cystic duct is blocked," Field says. Nausea, vomiting, and fever can accompany an attack, which can last several hours. Any foods--but particularly fatty foods--can precipitate an attack. Obesity, pregnancy, diabetes, prolonged fasting, cystic fibrosis, certain medications, or a high-calorie diet can increase your chances of developing gallstones. The condition becomes more common as you age.

Women are twice as likely as men to develop gallstones, particularly those in their childbearing years with a family history of gallstones. Women who have been pregnant develop the disease more often than women who haven't been, which probably is related to the drastic change in cholesterol and bile acid metabolism that occurs during pregnancy, Field says.

If your physician determines that your problem is serious, your gallbladder may need to be removed in a procedure called a cholecystectomy. Most surgeries are performed laparascopically, without the need for a large incision or a long hospital stay. Half a million gallbladder surgeries are performed every year, Field says.

Researchers are looking at the role of diet in the development of cholesterol gallstones. Eating patterns, calorie content, and composition of meals may be relevant to the disease.

If you think you have symptoms of gallstone disease, see your doctor.