How is alcohol metabolized in the body

People with this genetic mutation do not like to drink alcohol. Learn more about oxidation. The rate of metabolism remains constant during continued drinking. Why is this important? So, alcohol begins to accumulate in the bloodstream, giving an increased blood alcohol concentration BAC Figure 1. In other words, when the metabolism of ethanol is limited by the number of ADH enzyme molecules present, it proceeds independent of the amount of alcohol in the bloodstream.

With more than one drink of alcohol, the enzymes become saturated with ethanol molecules. Some ethanol is metabolized in the liver, but the rest of the ethanol leaves the liver and accumulates in the bloodstream. Alcohol that is not metabolized on its first passage through the liver continues to circulate throughout the body as an active drug.

Ultimately, only a small fraction of the ingested alcohol escapes metabolism. Please read the Duke Wordpress Policies. Contact the Duke WordPress team. The Alcohol Pharmacology Education Partnership. Schwartz-Bloom, Ph. Fulton T. Crews, Ph. Linda J. Porrino, Ph. David P. Friedman, Ph. ADH helps convert alcohol to acetaldehyde. Acetaldehyde is only in the body for a short time because it is rapidly converted to acetate by other enzymes.

Although acetaldehyde is present in the body a short period of time, it is highly toxic and a known carcinogen.

Most of the alcohol is metabolized by the liver as described above, but small amounts are eliminated from the body by forming fatty acid ethyl esters FAEEs , compounds that have been found to damage the liver and pancreas. Lastly, a small quantity of alcohol is not metabolized and is instead eliminated in the breath and urine, which is how BAC is measured in breath and urine tests.

Acetaldehyde can cause significant damage to the liver because that is where most alcohol is broken down into the toxic by-product. That said, some alcohol is instead metabolized in the pancreas and the brain, where acetaldehyde can also damage cells and tissues.

Small amounts of alcohol are metabolized in the gastrointestinal tract, which can also be damaged by acetaldehyde. Some researchers believe the effects of acetaldehyde go beyond the damage it can cause to tissues, but might also be responsible for some of the behavioral and physiological effects attributed to alcohol.

When researchers administered acetaldehyde to laboratory animals it caused incoordination, memory impairment, and sleepiness. Other researchers claim it is not possible for acetaldehyde alone to cause these effects because the brain protects itself from toxic chemicals in the blood with its unique blood-brain barrier.

Nevertheless, when the enzymes catalase and CYP2E1 metabolize alcohol—which only happens when large amounts are consumed —acetaldehyde can be produced in the brain itself.

The size of the liver and body mass of the drinker are factors in how much alcohol a person can metabolize in an hour, but research tells us that the genetic makeup of the individual is probably the most significant factor in how efficiently alcohol is broken down and eliminated. Simply put, this means some people have enzymes that can break down alcohol to acetaldehyde or acetaldehyde to acetate, more quickly than others. If someone has a fast-acting ADH enzyme or a slow-acting ALDH enzyme, they can have toxic acetaldehyde build up in the body, which can create dangerous or unpleasant effects when they drink alcohol.

Women absorb and metabolize alcohol differently from men. Research has shown that women may have less ADH enzyme activity in the stomach, allowing a larger percentage of alcohol to reach the blood before being metabolized. This could be one reason women who drink are more susceptible to alcohol liver disease, heart muscle damage, and brain damage than men. Genetics can also be a factor in whether or not the person is susceptible to developing alcohol use disorders.

For example, there is one variation of these enzymes that causes a build-up of acetaldehyde to the point it causes facial flushing, nausea, and a rapid heart rate. These effects can occur with even moderate alcohol consumption. This gene variant is common in people of Chinese, Japanese, and Korean descent, who may drink less because of the unpleasant side effects. Their gene variant has a protective effect against developing alcoholism.

According to the National Library of Medicine NLM , alcohol use disorder does not have a clear pattern of genetic inheritance, but the children of people with alcohol use disorder are still two to six times more likely than the general population to develop problems with alcohol use themselves. This increased risk may, in part, be a result of some shared genetic factors, but experts also believe that shared environmental and social factors likely are at play as well.

In the United States, more Native Americans die of alcohol-related causes than any other ethnic group, but researchers found there is no difference in the enzyme patterns or alcohol metabolism rates of Native Americans and Caucasians, indicating that there are other factors at play in the development of alcohol-related problems.

Heavy or chronic alcohol consumption has been linked to a long list of negative health consequences and long-term adverse effects. Some of these health problems have been directly linked to how alcohol is metabolized in the body and the production of acetaldehyde. The toxic effects of acetaldehyde have been linked to the development of cancers of the mouth, throat, upper respiratory tract, liver, colon, and breasts.

Ironically, the genes that "protect" some individuals from developing alcoholism may actually increase their vulnerability to developing cancer. Although they are less likely to drink large amounts of alcohol, these people are at greater risk for developing cancer because their bodies produce more acetaldehyde when they do drink. So, even some moderate drinkers are a greater risk of developing cancer. Because the liver is the organ that metabolizes most of the alcohol in the body and therefore is where most of the acetaldehyde is produced, it is particularly vulnerable to the effects of alcohol metabolism.

Because some alcohol metabolism also takes place in the pancreas, it is exposed to high levels of acetaldehyde and FAEEs. Additionally, despite the fact that more Native American people die of alcohol-related causes than do any other ethnic group in the United States, research shows that there is no difference in the rates of alcohol metabolism and enzyme patterns between Native Americans and Whites Alcohol metabolism and cancer— Alcohol consumption can contribute to the risk for developing different cancers, including cancers of the upper respiratory tract, liver, colon or rectum, and breast This occurs in several ways, including through the toxic effects of acetaldehyde Alcohol is metabolized in the body mainly by the liver.

The brain, pancreas, and stomach also metabolize alcohol. Many heavy drinkers do not develop cancer, and some people who drink only moderately do develop alcohol-related cancers. Ironically, the very genes that protect some people from alcoholism may magnify their vulnerability to alcohol-related cancers. The International Agency for Research on Cancer 21 asserts that acetaldehyde should be classified as a carcinogen. Acetaldehyde promotes cancer in several ways—for example, by interfering with the copying i.

Studies have shown that people who are exposed to large amounts of acetaldehyde are at greater risk for developing certain cancers, such as cancers of the mouth and throat 5. Although these individuals often are less likely to consume large amounts of alcohol, Seitz and colleagues 5 suggest that when they do drink their risk for developing certain cancers is higher than drinkers who are exposed to less acetaldehyde during alcohol metabolism.

Acetaldehyde is not the only carcinogenic byproduct of alcohol metabolism. ROS can damage proteins and DNA or interact with other substances to create carcinogenic compounds Poor nutrition may cause the mother to metabolize alcohol more slowly, exposing the fetus to high levels of alcohol for longer periods of time Increased exposure to alcohol also can prevent the fetus from receiving necessary nutrition through the placenta In rats, maternal malnutrition has been shown to contribute to slow fetal growth, one of the features of FASD, a spectrum of birth defects associated with drinking during pregnancy These findings suggest that managing nutrition in pregnant women who drink may help to reduce the severity of FASD More than 90 percent of people who drink heavily develop fatty liver, a type of liver disease.

Yet only 20 percent will go on to develop the more severe alcoholic liver disease and liver cirrhosis Alcoholic pancreatitis— Alcohol metabolism also occurs in the pancreas, exposing this organ to high levels of toxic byproducts such as acetaldehyde and FAEEs 3. Still, less than 10 percent of heavy alcohol users develop alcoholic pancreatitis—a disease that irreversibly destroys the pancreas— suggesting that alcohol consumption alone is not enough to cause the disease.

Researchers speculate that environmental factors such as smoking and the amount and pattern of drinking and dietary habits, as well as genetic differences in the way alcohol is metabolized, also contribute to the development of alcoholic pancreatitis, although none of these factors has been definitively linked to the disease Two methods that are helping researchers gain a better understanding of how alcohol is metabolized are the alcohol clamp method, in which alcohol is given intravenously, and the use of specially grown cells.

The alcohol clamp method. The speed at which people absorb, distribute, and metabolize alcohol varies as much as three or four times between individuals 1,2. The alcohol clamp is a method of administering alcohol intravenously to subjects, allowing researchers to circumvent variations in alcohol absorption. This technique enables researchers to administer precise doses of alcohol to achieve an exact breath alcohol concentration a measure of how much alcohol is in the body 3,4.

The actual dose of alcohol is calculated for each individual based on his or her specific alcohol elimination rate, controlling for factors like gender and body mass. This allows researchers to compare the alcohol elimination or metabolism rates without complicating factors. For example, using the alcohol clamp method researchers were able to determine that male volunteers eliminated alcohol at significantly faster rates than did female volunteers 5—8.

The alcohol clamp method also helps researchers study the genetics of alcohol metabolism, including differences in how volunteers who carry different versions of the ADH and ALDH genes metabolize alcohol 9.

Cultured cells. Cells that are grown in the laboratory i. Additionally, because large quantities of cells can be cloned, researchers are able to repeat experiments many times in order to confirm findings. Variability of ethanol absorption and breath concentrations during a large-scale alcohol administration study. Alcoholism: Clinical and Experimental Research —, Gender and ethnic differences in alcohol metabolism. Clamping breath alcohol concentration reduces experimental variance: Application to the study of acute tolerance to alcohol and alcohol elimination rate.

The alcohol clamp: Applications, challenges and new directions. Gender differences in alcohol metabolism: Relationship to liver volume and effect of adjusting for body mass. Gastroenterology —,