What Causes Gallstones?

Medically Reviewed

Gallstones are small stones that form in the gallbladder. An estimated 25 million people in the United States have gallstones. Women are twice as likely as men to have them. In fact, nearly 25 percent of women develop gallstones by age 60, and as many as 50 percent of women develop them by age 75. In contrast, only 20 percent of men have had gallstones by age 75.

There are two types of gallstones. Nearly 80 percent are cholesterol gallstones, which are made up of cholesterol, the fatty substance that forms our cell membranes. The remaining 20 percent are pigment stones, which are primarily made of bilirubin, the breakdown product of hemoglobin.

Causes of gallstones

Gallstones form when there is too much cholesterol or bilirubin in the bile to stay in solution. These substances then can precipitate to form small stones (“sludge”). If the gallbladder doesn’t empty as it should, the sludge accumulates and can form larger stones that may produce symptoms.

Humans normally secrete a lot of cholesterol into bile to eliminate it from the body. This can be made worse by eating a diet high in cholesterol or losing weight rapidly. Excess bilirubin is excreted if red blood cells are destroyed too rapidly.

Risk factors for the development of cholesterol gallstones include a genetic predisposition (particularly in people of Pima Indian or Scandinavian ancestry); being older than 50; obesity; pregnancy; use of medications such as estrogen, oral contraceptives or the antibiotic ceftriaxone (Rocephin); prolonged intravenous feeding; rapid weight loss; and diseases of the terminal ileum (the last portion of the small intestine, which is responsible for reabsorption of bile acids from the bowel into the blood).

Research has suggested that a deficiency of magnesium—an essential mineral found in green vegetables, fish, whole grains, legumes, seeds and nuts—might be a risk factor as well. People with hemolytic anemia or a bacterial infection inside the bile ducts are at risk for pigment gallstones.