Drinking alcohol raises the risk of cancer by damaging DNA, scientists have discovered for the first time, leading health experts to call for people to cut down on their consumption.
A study by the Medical Research Council Laboratory of Molecular Biology at Cambridge University has found that when the body processes alcohol it produces a chemical called acetaldehyde, which is harmful to DNA.
The damage happens in blood stem cells, which create the red and white blood cells that carry oxygen through the body and help fight infections.
Researchers found acetaldehyde snaps stem cell DNA, permanently altering the genetic code and triggering cancer.
Experts and charities described the findings, reported in 'Nature', as "very important" and urged people to drink less.
Professor Linda Bauld, Cancer Research UK's expert on cancer prevention, said: "This thought-provoking research highlights the damage alcohol can do to our cells, costing some people more than just a hangover. "It's a good idea to think about cutting down on the amount you drink."
Alcohol is linked to seven types of cancer: liver, breast, bowel, upper throat, mouth, oesophagal and larynx.
To find out how it damages the body, scientists gave diluted alcohol to mice then sequenced their DNA and analysed their chromosomes.
They discovered that drinking causes genetic breaks which rearrange chromosomes, and alter the DNA blueprint which keeps the body healthy.
Professor Ketan Patel, lead author of the study, said: "Some cancers develop due to DNA damage in stem cells.
"While some damage occurs by chance, our findings suggest that drinking alcohol can increase the risk of this damage."
The study also found some people carry genetic mutations in two genes - aldh2 and Fancd2 - which make drinking far more dangerous.
People of Chinese heritage are more likely to have the defects, which could explain the increased prevalence of oesophageal cancer in China, the authors said.
Prof Patel added: "Our study highlights that not being able to process alcohol effectively can lead to an even higher risk of alcohol-related DNA damage and therefore certain cancers."
Commenting on the findings, Magdalena Zernicka-Goetz, Professor of Mammalian Development and Stem Cell Biology at Cambridge, said: "This is very important work."
Malcolm Alison, Professor of Stem Cell Biology at the Barts Cancer Institute, Queen Mary University of London, added: "Drinkers beware: most of our organs and tissues have stem cells, immortal cells that replenish cells lost through the likes of old age throughout our lives."