Gallstones are small stones that form in the gallbladder, usually due to a chemical imbalance in the composition of bile inside the gallbladder. Bile is produced by the liver to aid the breakdown of lipids. This chemical imbalance causes tiny crystals to form in the bile, which eventually leads to stones developing.
The majority of gallstones are caused by a high cholesterol level increasing the cholesterol content of the bile.
Other factors that increase the likelihood of cholesterol gallstones forming include inadequate emptying of the gallbladder and infrequent gallbladder movement. This can impair outflow of the bile from the gallbladder, causing it to stagnate. This is referred to as biliary cholestasis.
The bile gradually becomes more concentrated in the liver and predisposes to stone formation. Cholesterol gallstones range in colour form light yellow to dark brown and account for 4 out of 5 cases of gallstones.
Pigment gallstones are small stones that form as a result of raised bilirubin levels. Bilirubin is produced as a result of red blood cells being broken down. The bilirubin and heme pigments present in these stones means they are dark coloured instead of a yellow–white colour.
Pigment stones are rare in the general population and only account for one in five gallstone cases. These stones are, however, a common symptom in people with hemolytic anemia or erythropoietic protoporphyria.
Risk factors for gallstones
Some people are at a greater risk of developing gallstones than others. Some of the factors that increase this risk include:
- Female gender – The presence of estrogens is thought to increase the risk of cholesterol stones developing.
- Women on the combined contraceptive pill or estrogen hormone therapy are at a higher risk of developing the stones.
- Obesity and overweight (a body mass index of 25 or above)
- Age 40 years or older
- Disorders of the digestive system such as Chron’s disease or irritable bowel syndrome
- A family history of gallstones
- Rapid weight loss due to dieting or weight loss surgery