New human carcinogen
Acetaldehyde associated with consumption of alcoholic beverages is classified as a new human carcinogen by International Agency for Research on Cancer (IARC). It belongs to the same Group 1 as asbestos, formaldehyde, benzene, and radon.
The specificity of acetaldehyde as a human carcinogen is based on a unique human cancer model caused by a gene mutation. Gene mutation has randomized tens of thousands of alcohol drinking East Asians to 2-3-fold higher exposure to acetaldehyde every time they drink alcohol. As a result their risk for upper digestive tract cancer risk (oral, pharyngeal, esophageal and gastric cancer) is 4 to 12 times higher compared to alcohol users without the gene mutation. A causal relationship between alcohol associated acetaldehyde and upper digestive tract cancers has been clearly demonstrated with this model.
Probably the most common carcinogen in the world
Acetaldehyde is present in almost all alcoholic beverages and food stuffs produced by fermentation. Acetaldehyde associated with alcoholic beverages comes from their free acetaldehyde, as well as, from the locally generated acetaldehyde in alcohol combustion process. Most of free acetaldehyde is in strong rice and fruit spirits (rice spirits, Tequilas, Calvados, sherry). In wine’s most of free acetaldehyde is bound to sulfites.
Acetaldehyde is also the most abundant carcinogenic compound of tobacco smoke that dissolves easily into the saliva during smoking and through saliva is distributed to the mucosa of the whole upper digestive tract.
Acetaldehyde is naturally present in some food products, for example in apples and bananas. Acetaldehyde concentration of yogurt is achieved by using in the fermentation process two types of microbes both of which are very good acetaldehyde produces.
Due to its pleasant apple-like smell, acetaldehyde is also used as a flavouring in some pastries, fruit juices, soft drinks, sweet desserts and dairy products.
How does acetaldehyde generate in the human body?
Over 90 % of ingested alcohol and 100 % of acetaldehyde generated in the liver is metabolized in the liver. Thus measurable levels of acetaldehyde are not released from the liver to the blood circulation
Highest acetaldehyde concentrations after alcohol intake are found in saliva and gastric juice. This is because alcohol is metabolized to acetaldehyde locally by normal oral microflora and mucosal cells. Under certain conditions, microbes produce acetaldehyde also from sugar. Oral microbes and mucosa have insufficient capacity to metabolize acetaldehyde, consequently, the highest acetaldehyde concentrations are found in the saliva and gastric contents of stomachs. These organs precisely has the highest cancer risk after alcohol intake.
In a normal, healthy stomach, hydrochloric acid (HCI) kills the acetaldehyde-producing microbes (yeasts and bacteria) of the digestive tract, which are carried from the mouth to the stomach with saliva. In some people, acid-producing cells of the mucous membrane of the stomach disappear due to atrophy of the mucous membrane (a condition called atrophic gastritis), and therefore microbes are able to multiply in the stomach. The same goes for people who have used PPI products to treat gastric acid disorders.