Alcohol Sensitivity

Alcohol Sensitivity

The active ingredient in alcoholic drinks is ethanol, which is commonly referred to as alcohol. Ethanol is produced by yeasts that digest sugar in certain carb-rich foods (such as grapes to make wine and grains to make beer). Drinking alcohol affects your mental state and your behaviour. Excessive drinking worsens these effects and also results in the feeling of being hungover (which is caused by a combination of increased levels of acetaldehyde, hormonal alterations, dehydration and decreased levels of glucose).

What is the ALDH2 gene?

The ALDH2 gene encodes for the enzyme aldehyde dehydrogenase. This enzyme is involved in alcohol metabolism and oxidises alcohol to a non-toxic form that can then be excreted. ALDH2 is especially abundant in the liver where over 90% of alcohol consumed is metabolised.

What is the effect of genetic variation in the ALDH2?

Genetic variation at the ALDH2 gene dramatically reduces the activity level of the ALDH2 enzyme and so reduces its ability to metabolise alcohol. Individuals with one allele have almost 40%  enzyme activity and individuals with two alleles have nearly 50% enzyme activity compared to individuals with no SNP.

This dramatic reduction in the ability to metabolise alcohol leads to accumulation of acetaldehyde in circulation even after a moderate amount of alcohol intake - hence why the presence of alleles can cause the well-known Asian Flushing Syndrome. Individuals with ‘risk’ alleles also heightened unpleasant reactions to alcohol, such as nausea, vomiting, hypotension, and/or rapid heartbeat (i.e., tachycardia) and worse hangovers when they consume alcohol.

How does the genetic variation vary worldwide?

The presence of allele at the ALDH2 gene is essentially absent among Europeans, but is highly prevalent among East Asians - hence the origin of the term ‘Asian flush’.

Does genetic variation in ALDH2 affect the risk of alcohol dependence?


The presence of an allele reduces an individual’s ability to metabolise alcohol and also have a protective effect in regard to alcoholism. The inactive ALDH2 gene leads to the accumulation of acetaldehyde which results in feelings of cardiovascular effects, dysphoria, palpitations, dry mouth, headache, nausea and facial warning as a result of consuming even a very small amount of alcohol. These unpleasant effects often lead to individuals abstaining from further alcohol consumption, thereby reducing their susceptibility to develop alcoholism.

Alcohol is always a very personal choice based upon everyone’s personal circumstances, but it is recommended that men and women should not drink more than 14 units a week and that this intake should be spread over three or more days.

A large glass of wine contains 3 units.

A can of large/beer/ cider contains 2 units.

A bottle of wine contains 10 units.

What are the causes and signs of alcoholism?

A number of different factors can predispose individuals to alcohol addiction, such as family history, social environment, mental health and genetics.

Many signs of alcohol dependence exist, characterized by alcohol cravings, inability to abstain or loss of self-control when drinking. As a rule of thumb, if alcohol is adversely affecting an individual’s quality of life, they may have a problem with alcohol dependence or alcoholism and they should seek advice from a doctor.

Why is the liver in particular vulnerable to excess alcohol drinking?

Alcohol is metabolized in the liver and this is why the liver is most vulnerable to damage by excess alcohol intake.

Frequent alcohol intake can lead to increased fat inside liver cells, which is usually symptomless and fully reversible. In heavy drinkers, the liver becomes inflamed which can lead to cirrhosis (in which liver cells die and get replaced with scar tissue).

Backed by Science

Our in-house scientists have sorted through thousands of studies and we only use genes that are backed by a significant body of peer-reviewed research. Check out Nell’s Science Standard for more information.