Research published yesterday in Nature shows how alcohol damages DNA in stem cells, helping to explain why drinking increases the risk of cancer.

For the study, scientists at the MRC Laboratory of Molecular Biology gave ethanol to mice. They then used chromosome analysis and DNA sequencing to examine the genetic damage caused by acetaldehyde, which is produced when the body processes alcohol. They found that acetaldehyde can break and damage DNA within blood stem cells leading to rearranged chromosomes and permanently altering the DNA sequences within these cells.

"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," explains Ketan Patel, lead author of the study.

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The study also examined how the body tries to protect itself against damage caused by alcohol. The first line of defense is a family of enzymes called aldehyde dehydrogenases (ALDH). These enzymes break down harmful acetaldehyde into acetate, which our cells can use as a source of energy. In people who lack these enzymes, acetaldehyde builds up and causes a flushed complexion as well as sick feeling.

In the study, when mice lacking the ALDH enzyme—ALDH2—were given alcohol, it resulted in four times as much DNA damage in their cells compared to mice with the fully functioning ALDH2 enzyme.

The second line of defense used by cells is a variety of DNA repair systems that, most of the time, allow them to fix and reverse different types of DNA damage. But they don't always work and some people carry mutations that mean their cells aren't able to carry out these repairs effectively.

"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. But it's important to remember that alcohol clearance and DNA repair systems are not perfect and alcohol can still cause cancer in different ways, even in people whose defense mechanisms are intact," Patel adds.