Acetaldehyde is a chemical compound with the formula CH3CHO, often recognized by its pungent, fruity odor. While small amounts can be found in foods like coffee, bread, and ripe fruit, alcohol consumption is a major source of exposure to this substance in the human body. Acetaldehyde is considered a toxic byproduct of alcohol metabolism, contributing to various discomforts and posing health risks due to its highly reactive nature.
How Alcohol Becomes Acetaldehyde
When alcohol, specifically ethanol, is consumed, it is primarily absorbed into the bloodstream from the stomach and small intestine. The liver plays the main role in metabolizing approximately 90% of the ingested ethanol. This detoxification process involves a series of enzymatic reactions designed to break down alcohol and eliminate it from the body.
The initial step in alcohol metabolism involves the enzyme alcohol dehydrogenase (ADH), which is mainly found in the liver. ADH converts ethanol into acetaldehyde, a highly toxic substance.
Following this, acetaldehyde is rapidly processed by another enzyme called aldehyde dehydrogenase (ALDH), particularly aldehyde dehydrogenase 2 (ALDH2). ALDH converts acetaldehyde into acetate, a much less toxic compound. Acetate is then further broken down into carbon dioxide and water, which the body can easily excrete.
Health Impacts of Acetaldehyde
The harmful effects of acetaldehyde stem from its highly reactive nature, allowing it to interact with proteins, lipids, and DNA. When acetaldehyde accumulates in the body, it can disrupt the function of these components. This accumulation is a primary cause of common hangover symptoms.
Immediate effects of acetaldehyde buildup can include facial flushing, nausea, headaches, and a rapid heartbeat. These symptoms are often linked to the acetaldehyde-induced release of signaling molecules like epinephrine and norepinephrine, which typically trigger the body’s fight-or-flight response.
Beyond acute discomfort, prolonged exposure to acetaldehyde from regular heavy drinking raises concerns about long-term health problems. Acetaldehyde is classified as a probable human carcinogen. It can damage DNA by forming adducts and causing double-stranded breaks, contributing to tumor development.
Why Some People React Differently
Individual responses to alcohol consumption can vary due to genetic differences in how the body processes acetaldehyde. A common genetic variation involves the aldehyde dehydrogenase 2 (ALDH2) enzyme. Some individuals possess a variant of the ALDH2 gene that produces a less active or inactive version of this enzyme.
This less efficient ALDH2 enzyme leads to a buildup of acetaldehyde in the bloodstream after alcohol consumption. The accumulation of acetaldehyde causes blood vessels to open, resulting in symptoms like facial flushing, often referred to as “Asian flush” or “alcohol flush reaction.” Other symptoms can include nausea, vomiting, headaches, and a stuffy nose.
This ALDH2 deficiency is particularly prevalent in populations of East Asian descent, affecting an estimated 36% to 70% of individuals in these groups, or about 8% of the global population. While this genetic variation can discourage heavy drinking due to the unpleasant symptoms, individuals with ALDH2 deficiency who consume alcohol regularly may face a higher risk for certain diseases, including specific cancers and cardiovascular issues.