Answer:

Some people can drink heavily without getting drunk, while others experience facial flushing after just a sip. This phenomenon is not solely due to tolerance but also depends largely on the body's ability to metabolize alcohol.

The liver is responsible for metabolizing about 90% of the ingested alcohol, with the remaining 10% excreted through sweat, urine, and breath. This process is carried out by two main enzymes: ADH (alcohol dehydrogenase) and ALDH2 (acetaldehyde dehydrogenase 2).

Upon entering the body, ethanol, the main intoxicating component in alcoholic beverages, is converted by the ADH enzyme into acetaldehyde, a neurotoxin. Immediately afterward, ALDH2 "detoxifies" by converting acetaldehyde into harmless acetic acid. This substance is eventually broken down into water and CO2 and then expelled.

Problems arise when one of the two enzymes above doesn't function efficiently. If ADH is too active, acetaldehyde is produced rapidly, overwhelming the body's processing capacity, leading to nausea and fatigue. More dangerously, if ALDH2 is weak or deficient, acetaldehyde accumulates in the blood, causing typical symptoms of intoxication such as facial flushing, headaches, dizziness, and nausea.

The difference in the activity of these two enzymes creates varying "thresholds" for alcohol tolerance in each individual. People with well-functioning ALDH2 enzymes metabolize toxins quickly and get drunk less easily. Conversely, those with weak ALDH2 enzymes can become intoxicated after just a few drinks.

In a healthy adult, the liver can process an average of one unit of alcohol per hour. This means that if you drink 5 units, your body needs at least 5 hours to completely eliminate it. However, this is just a reference figure, as the rate of alcohol absorption and elimination is also affected by other factors such as weight, age, liver health, and the amount of food in the stomach.

Doctor Nguyen Huy Hoang

Vietnam Society of Underwater and Hyperbaric Medicine