Alcohol metabolism: How long does it stay in your system?

E njoying a tipple is one of life’s pleasures but is not without its perils. Alcohol is a toxin and while moderate, occasional drinking is unlikely to lead to significant health problems, long-term regular drinking can increase the risk of a range of life-limiting conditions including several types of cancers and coronary heart disease.

But that’s rarely a consideration when the sun is out, and there’s a cold bottle of chablis in the fridge. What makes alcohol so pleasant also makes it easy to overindulge, and when we do, the body works hard to deal with the effects.

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How alcohol is processed in the body

Alcohol is a depressant, meaning it slows the brain’s control of the body. Even a small amount can affect important functions like speech and movement. Drinking very large amounts all at once can slow your heart rate and breathing down to a dangerously low level.

In order to neutralise alcohol and clear it from the system the body metabolises it through a series of complex biochemical processes.

Debbie Shawcross, a professor of hepatology and chronic liver failure at the Institute of Liver Studies, King’s College London, explains: “After having an alcohol-containing drink, about a quarter of the alcohol is absorbed straight from your stomach into the bloodstream. The rest is mostly absorbed from your small bowel.”

The rate at which the alcohol passes into the bloodstream depends on a range of factors, such as:

Drinks with a higher alcohol concentration are generally absorbed faster. Carbonation can also make alcohol pass into the bloodstream faster. A 2006 study found that the use of a carbonated mixer had varying effects on the alcohol absorption rate. Two thirds of the 21 subjects studied absorbed the alcohol with the carbonated mixer at a faster rate, with the remaining third showing either no change or a decrease in rate.

Once alcohol has entered the bloodstream it starts to be processed, mainly by the liver (90-98 per cent) and also by the kidneys (2-10 per cent). A small percentage is also expelled in your breath or excreted in your sweat.

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Prof Shawcross explains that the liver breaks down alcohol in two different ways.

“Most of the alcohol is broken down by an enzyme in liver cells called alcohol dehydrogenase,” she says. “This breaks down alcohol into a chemical called acetaldehyde. Then another enzyme, aldehyde dehydrogenase, rapidly breaks the acetaldehyde down into acetate. Acetate is further broken down into carbon dioxide and water. A small amount of alcohol may be processed using a different set of enzymes in your liver. This alternative pathway, known as the microsomal ethanol-oxidising system, is mainly used when the level of alcohol in your blood is very high.”

Regular drinking can increase the activity of this second pathway, which can lead to the effects of alcohol being better tolerated.

Factors affecting alcohol metabolism

Genetics: Some people metabolise alcohol poorly due to a genetic variation in the levels of the enzymes that break down alcohol. Around 30-50 per cent of those of East Asian descent, for example, have a genetic variation in the aldehyde dehydrogenase enzyme that means they do not break down alcohol in the normal way, and shortly after drinking alcohol their acetaldehyde level rises. Acetaldehyde is a toxic substance that causes flushing of the face, hot sensations, nausea and palpitations.

Gender: Men typically have a 70-80 per cent higher level of gastric alcohol dehydrogenase activity compared to women, so more alcohol is absorbed and dealt with by their livers. Women also appear to be more adversely affected by binge drinking. A 2014 study found that after a single episode of binge drinking, women had more endotoxins from gut bacteria compared to men. These molecules initiate a host of damaging inflammatory responses.

Hormone levels also affect the body’s ability to process alcohol, and women will experience higher blood alcohol concentration (BAC) drinking a regular amount of alcohol before menstruation.

Food: Drinking alcohol with food slows its absorption and drinking on an empty stomach speeds it up.

Body composition: In general, the less you weigh the more you will be affected by a given amount of alcohol because the alcohol has less room to spread out, making the concentration higher. However, differences in body composition can also reduce the metabolism of alcohol. Alcohol enters all tissues of the body except bone and fat. If the percentage of fatty tissue is high, the alcohol can only be distributed throughout the remaining lean tissue resulting in a higher concentration for those areas.

For example, if two people of the same weight consume the same amount of alcohol, a person with a higher percentage of fat will reach a higher peak blood alcohol concentration than a lean, muscular individual because fatty tissue does not contain very much water and will not absorb very much alcohol, making the concentration in the rest of the body higher for the person with the higher percentage of fat.

Medication: As alcohol is a drug, it should be treated no differently than taking any two prescriptions at the same time. Certain medications, such as antidepressants, should not be mixed with alcohol. Even herbal medicines and supplements, such as chamomile, echinacea, St John’s Wort and valerian, can have adverse interactions with alcohol.

Age: As we age, the activity of the enzymes that break down alcohol reduce, which means that alcohol is more slowly metabolised and acetaldehyde levels take longer to be dealt with, which is why older people tolerate alcohol less. They also have less muscle mass.

How long does it take to sober up?

Studies have found that after you stop drinking, alcohol can stay in your blood for up to six hours and in your breath for 12-24 hours. It can take the liver several days to recover after a binge and sometimes up to weeks or months if the damage is severe.

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How can I manage my alcohol consumption or even sober up faster?

You can slow the rate alcohol passes into the bloodstream by eating before drinking and drinking slowly, and you can control the level of alcohol you drink by drinking less and having drinks with lower alcohol volumes. But the bad news is, once alcohol is in your bloodstream there is nothing you can do to speed up alcohol metabolism.

As for what to eat beforehand, consider opting for foods high in protein. A person who has not eaten will hit a peak BAC typically within 30 minutes to two hours of drinking. A person who has eaten will hit a peak BAC typically between one and six hours, depending on the amount of alcohol consumed.

As Prof Shawcross explains: “The liver metabolises alcohol at a very constant rate, approximately one drink per hour. If there is excessive alcohol in the blood, the liver cannot speed up the detoxification process. There are no ways to speed up alcohol metabolism and no ways to avoid a hangover.”

So guidelines recommend that singular drink per hour: this keeps the liver from being overloaded and enables a person to maintain a safe blood alcohol concentration while still achieving the social relaxation effect.

As for the week, government health guidelines advise men and women to limit alcohol to 14 units or less per week and to spread drinking over three or more days, having regular alcohol-free days each week.

Effects of alcohol on the body

Short-term

Long-term