Drinking a moderate amount of alcohol protects against the development of gallstones, UK researchers say.
Consuming two units a day cuts the chance of developing gallstones by a third, analysis of data from 25,000 men and women showed.
Gallstones are very common but symptoms and complications are only seen in three in 10 cases.
Delegates at a US conference heard that alcohol reduces cholesterol in the bile from which gallstones form.
The researchers used data from a large study set up to look at the link between diet and cancer in men and women in the 45-74 age range.
Alcohol intake was compared with the risk of developing symptomatic gallstones over a 10-year period.
Those who did develop the condition were an average of 62 years old and more than two-thirds were women.
They calculated that those in the highest alcohol group had a 32% lower risk than those who drank no or little alcohol.
For every unit of alcohol extra drunk per week, the risk of gallstones fell by 3%.
The researchers said it had been suggested that alcohol might reduce gallstones through its effects on cholesterol but the magnitude of the effect had not been calculated.
Cholesterol
Gallstones form in the gallbladder from bile and are generally made up of hardened cholesterol.
It is thought that around one in three women and one in six men get gallstones at some point in their life but they are more common in older adults.
Other factors which increase the chances of them forming include pregnancy, obesity, rapid weight loss and some medications.
Moderate alcohol below recommended limits is associated with good health
Professor Chris Hawkey, British Society of Gastroenterology
Study leader Dr Paul Banim, a clinical lecturer at the University of East Anglia and a specialist registrar in gastroenterology, said alcohol was known to increase levels of "good" HDL cholesterol which was also known to be protective against cardiovascular disease and which could alter the composition of cholesterol in the bile.
He said excessive alcohol intake can cause health problems but quantifying how much alcohol reduces the risk of gallstone development allows doctors to offer specific guidance.
His colleague Dr Andrew Hart, a senior lecturer in gastroenterology, said the findings boosted their understanding of how gallstones formed.
"Once we examine all the factors related to their development in our study in the UK, including diet, exercise, body weight and alcohol intake, we can develop a precise understanding of what causes gallstones and how to prevent them."
Professor Chris Hawkey, president of the British Society of Gastroenterology, said the study was interesting but should be interpreted with caution because it only measured an association.
"Nevertheless, previous research has found similar findings and it seems likely to be a real effect.
"The University of East Anglia are producing interesting data on consumption of particular foods and alcohol - for example a recent study from that unit suggests that oily fish may protect against ulcerative colitis.
"Moderate alcohol below recommended limits is associated with good health. But alcohol is addictive and drinkers must be careful not to escalate their intake."
The findings were presented at the Digestive Disease Week annual meeting in Chicago.
COMPLICATIONS OF GALLSTONES
Severe pain
Inflammation and infection
Jaundice
Source