Almost 30 years after discovery of a link between alcohol consumption and certain forms of cancer, scientists are reporting the first evidence from research on people explaining how the popularbeverage may be carcinogenic.

Silvia Balbo, Ph.D., who led the study, explained that the human body breaks down, or metabolizes, the alcohol. One of the substances formed in that breakdown is acetaldehyde, a substance with a chemical backbone that resembles formaldehyde. Formaldehyde is a known human carcinogen. Scientists also have known from laboratory experiments that acetaldehyde can cause DNA damage, trigger chromosomal abnormalities in cell cultures and act as an animal carcinogen.

“We now have the first evidence from living human volunteers that acetaldehyde formed after alcohol consumption damages DNA dramatically,” Balbo said. Acetaldehyde attaches to DNA in humans – to the genetic material that makes up genes – in a way that results in the formation of a ‘DNA adduct.’ It’s acetaldehyde that latches onto DNA and interferes with DNA activity in a way linked to an increased risk of cancer.

Balbo pointed out that people have a highly effective natural repair mechanism for correcting the damage from DNA adducts. In addition, most people have an enzyme called alcohol dehydrogenase, which quickly converts acetaldehyde to acetate, a relatively harmless substance.

However, about 30 percent of people of Asian descent – almost 1.6 billion people – have a variant of the alcohol dehydrogenase gene and are unable to metabolize alcohol to acetate. That genetic variant results in an elevated risk of esophageal cancer from alcohol drinking. Native Americans and native Alaskans have a deficiency in the production of that same enzyme.