The effects of alcohol consumption and intoxication on the mind and body are widely described. So are the symptoms of alcohol abuse, dependence, and withdrawal.
But have you ever wondered what happens to alcohol in your body? This is what we call the metabolism, in other words the breakdown, absorption and elimination of alcohol. You might have noticed that some people react differently to alcohol. One of the reasons is that there are individual differences in the way alcohol is processed in the body. This is the main reason why some people are more tolerant to alcohol than others. In this article we will try to explain, in a nutshell, the most important metabolic pathways of alcohol, and the side-effects of the by-products of alcohol metabolism.
Alcohol breakdown: what happens after drinking alcohol?
It should be remembered that the way everyone metabolizes alcohol depends on both genetic factors and environmental factors1. For example: the enzymes (small proteins) involved in alcohol breakdown vary from one person to another; this is due to genetic variations between individuals. The general nutritional status, i.e., how healthy, or not a person generally eats and drinks may also influence the metabolism of alcohol inside the body since healthy nutritional status contributes to health status of the organs.
For example: high quantities of alcohol (environmental factors) will have a bigger impact than low quantities on the detoxification process from the liver. The more you drink, the more effort is required from your liver.
When one speaks about alcohol, we actually refer to ethanol, the chemical name for alcohol. Ethanol is processed by the body through a series of breakdown steps.
The alcohol breakdown process starts in the liver by two enzymes: these help to accelerate further chemical reactions to take place, which in turn results in the formation of by-products:
- First, due to the enzyme alcohol dehydrogenase or ADH, the compound acetaldehyde is formed. Acetaldehyde is a very toxic as well as a potential carcinogenic substance and one of the reasons why alcohol consumption is not healthy. The acetaldehyde that is produced is then further broken down.
- This happens under the influence of another enzyme, ALDH, or aldehyde dehydrogenase, which breaks down the very toxic acetaldehyde into the slightly less toxic molecule called acetate.
So, in summary:
Alcohol ADH. Acetaldehyde ALDH Acetate2
Other body tissues then break down the circulating acetate in carbon dioxide and water.
The most damaging by-product of alcohol metabolism: acetaldehyde:
We all know that overconsumption of alcohol damages health. However, only few people realize that it is in fact the metabolite (the by-product) of the ethanol breakdown which is the more toxic molecule. The effects of acetaldehyde circulating in the body are unpleasant, and can become severe and dangerous when acetaldehyde levels are too high.
Effects can range in severity and differ in intensity between individuals and first present as: flushing, nausea and vomiting, rapid heartbeat (tachycardia), hypotension. They also lead to the lousy feeling of a “hang-over”.
Longer term and chronically raised levels of acetaldehyde seriously damages the liver: ranging from lipid accumulation in the liver (fatty liver) and inflammation to liver fibrosis and eventually cancer3.
The main organ affected by acetaldehyde is the brain: acetaldehyde intoxication, either over the short term or the long term, is a major cause of brain dysfunction such as memory trouble and disturbances in brain activity, central nervous system toxicity and inflammation. It can lead to irreversible neurological consequences.
Prenatal alcohol exposure in a pregnant mother is the cause of Fetal Alcohol Spectrum Disorder which presents by congenital motor and cognitive disabilities, such as lower intelligence, memory deficits, language and communication skills.
Added to that, alcohol abuse leads to thiamin (vitamin B1) depletion and other vitamin deficiencies, which further aggravate cognitive and motor functioning4.
On the other hand, some alcoholic beverages, such as red wine, contain molecules that have a beneficial effect on the cardiovascular system. However, the disadvantage of the alcohol might not outweigh the benefit of the health promoting molecules.
Take away message:
Alcohol is deeply ingrained and accepted in socializing events because of its disinhibitory effects. However, the understanding of the negative consequences are starting to outweigh this general acceptance. Because the alcohol metabolism depends on genetic and environmental factors, it is highly individual. And some people may “handle” toxic effects of alcohol metabolites better than other people. When confronted to chronic consumption or overconsumption of alcohol, we advise you to carefully consider the detrimental effects of ethanol metabolites. There is a reason why alcohol is not healthy.
The most important message you need to keep in mind is to always remain conscious of the quantity of alcohol you want to drink and know your limits!
- Mews, P., Egervari, G., Nativio, R. et al.Alcohol metabolism contributes to brain histone acetylation. Nature 574, 717–721 (2019). https://doi.org/10.1038/s41586-019-1700-7