The causes of gallstones are not fully understood, but there are several contributing factors. They include:

• Excess cholesterol. When bile contains too much cholesterol, it cannot be dissolved by bile salts. This causes cholesterol to crystalize and possibly form into gallstones.
  
  
• Inadequate gallbladder emptying. If the gallbladder does not empty frequently enough or completely enough, bile can become too concentrated. This contributes to the formation of gallstones. This may happen during pregnancy. Eating too little or avoiding food for long periods of time can decrease gallbladder contractions.

In addition, there are many factors that increase the risk of developing gallstones. They include:

• Gender. Women between the ages of 20 and 60 are more likely to develop gallstones than men.
  
  
• Body weight. People who are obese (particularly women with waistlines exceeding 35 inches) and those who have lost weight rapidly have a greater risk of developing gallstones. Fasting also increases the risk. Research also indicates that men who lose and then regain weight (“weight cycling”) have an increased risk of developing gallstones.
  
  
• Age. The risk of developing gallstones increases with age. People over age 60 face the highest risk.
  
  
• Ethnicity. Gallstones develop more frequently in people of Native American, Hispanic and western Caucasian heritage. African Americans, natives of South Africa and Japanese populations have the lowest rate.
  
  
• Personal history. People who have previously developed gallstones are more likely to develop them again.
  
  
• Family history. The development of gallstones tends to run in families.
  
  
• Estrogen levels. Increased levels of the female hormone estrogen may increase the risk of gallstones by increasing cholesterol levels in bile and decreasing gallbladder movement. Pregnant women, women using hormonal methods of birth control (e.g., oral contraceptives) and postmenopausal women undergoing hormone replacement therapy all have a greater likelihood of developing gallstones.
  
  
• Diseases of the gallbladder and bile ducts. People with disorders of the gallbladder or bile ducts, such as bile duct cysts, are at increased risk for gallstones.
  
  
• Other diseases. People with diseases that involve the small intestine such as Crohn's disease, and metabolic diseases such as diabetes face a higher risk of gallstones. Liver diseases such as cirrhosis may also increase the risk of gallstones.
  
  

  

  
  
• Conditions associated with rapid destruction of red blood cells, such as sickle cell anemia, increase the risk of developing gallstones by causing excess bilirubin in the bile.
  
  
• Medications. Hormonal medications (especially those containing estrogen) may promote gallstones. A hormonal medication used for acromegaly (a disease characterized by excess production of growth hormone) may cause gallstones. Cholesterol lowering medications also increase the risk of developing gallstones by increasing the amount of cholesterol secreted in bile. There are also concerns that a relatively common prescription weight-loss drug may increase gallstone risk in patients.
  
  
• Parenteral nutrition. People who cannot take food by mouth or through their stomachs may receive nutrients through a tube inserted in their veins. These people may have an increased risk of developing gallstones.