Alcohol Metabolism: How much alcohol an individual’s body can break down in a given period of time varies widely and depends on a range of factors, including liver size, body mass, genetics and habitual alcohol consumption. When we drink alcoholic beverages, enzymes in our body break down the alcohol (ethanol) molecule, resulting in the formation of a compound called acetaldehyde. Another enzyme quickly turns acetaldehyde into acetate, which in turn is split into carbon dioxide and water to be eliminated from the body. The bulk of this activity takes place in the liver, although some alcohol metabolism also happens in the stomach, pancreas, and brain.
Acetaldehyde is toxic and has the potential to cause significant damage. This is one reason drinking heavily puts people at risk for adverse health consequences like liver damage, pancreatitis, and various cancers.
Alcohol and Health: Let’s take a look at some of the ways alcohol consumption impacts various body systems:
The Brain: The most obvious effects of drinking in the short term are changes to things like mood, behavior, and coordination. These occur because alcohol interferes with the brain’s communication pathways. Studies examining the longer-term impact of alcohol intake on cognitive function have yielded mixed results. A recent cohort study published in the journal Neurology that followed nearly 20,000 middle-aged or older participants for nine years found that low to moderate alcohol intake (compared with never drinking) was associated with higher cognitive scores and lower rates of cognitive decline, particularly in participants identifying as white. But a 2020 meta-analysis found each additional drink per week was associated with nearly four percent higher risk of developing mild cognitive impairment (MCI). Heavy alcohol intake (defined in this study as more than 14 drinks per week) was associated with higher risk of progression from MCI to dementia.
The Liver: Since most alcohol metabolism takes place in the liver, this organ is most susceptible to alcohol’s effects. It is common for people who drink heavily to develop alcoholic fatty liver disease. While fatty liver typically has no symptoms, it can cause liver inflammation (alcoholic hepatitis), which damages the liver and creates scarring (fibrosis), eventually leading to cirrhosis that can cause liver failure. While abstaining from drinking alcohol can reverse alcoholic fatty liver disease, these more advanced conditions are irreversible.
Prolonged heavy drinking can also contribute to pancreatitis, a condition in which the blood vessels of the pancreas become dangerously inflamed.
The Cardiovascular System: Much attention has been paid to data that drinking moderate amounts of alcohol—red wine in particular—is good for heart health. Unfortunately, there are limitations to the studies providing these data. “Most research on the impact of alcohol on health has been observational,” says Alice H. Lichtenstein, DSc, senior scientist and director of the Cardiovascular Nutrition Laboratory and executive editor of Tufts Health& Nutrition Letter. “Hence, there is no proof that moderate alcohol consumption by itself offers a significant protective effect. People who report moderate alcohol intake (as opposed to heavier intake) often make other healthier diet and lifestyle choices as well. While studies try to control for the effect of these other choices (like engaging in physical activity and avoiding tobacco), it is difficult to determine how much cardio-protective and other benefits can be attributed to alcohol alone.”
Cancer: The National Toxicology Program of the U.S. Department of Health and Human Services lists alcohol as a known human carcinogen. Research suggests intake of alcohol beyond moderate—particularly over time—is associated with higher risk of cancers of the head, neck, esophagus, liver, colon/rectum, and breast. “The issue of breast cancer is important for women at elevated risk due to family history or other risk factors as determined by their doctor,” says Lichtenstein. “Alcohol interferes with the breakdown of estrogen, increasing the risk of estrogen-sensitive breast cancer.”
The Immune System: Excess alcohol intake can weaken your immune system. Becoming inebriated may slow the body’s ability to ward of infections for up to 24 hours. Chronic intake of excess alcohol is associated with higher susceptibility to contagious diseases.
Sleep: According to the Sleep Foundation, as many as 20 percent of Americans use alcohol to help them fall asleep. While alcohol before bed may help you fall asleep more quickly, studies of brain patterns suggest drinking may block REM sleep—the most restorative kind of sleep. It may also make you more likely to wake up in the middle of the night by interrupting circadian rhythms and by acting as a diuretic, necessitating nighttime trips to the bathroom. Since alcohol is a muscle relaxant, it can make you more prone to snoring and sleep apnea by relaxing the muscles in the throat. Inadequate sleep has been associated with weight gain, anxiety, high blood pressure, irregular heartbeat, higher risk for diabetes, and heart disease.
Other Health Impacts: Research that has found associations between moderate alcohol intake and lower risk for conditions like cardiovascular disease, type 2 diabetes, and gallstones is often highly publicized. Potential benefits must, however, be balanced with the potential downsides of alcohol intake. A major global study published in 2018 concluded that alcohol was the leading risk factor for disease and death worldwide in 2016, accounting for nearly one in 10 deaths. In the U.S., alcohol has been reported to play a role in one in three cases of violent crime and is involved in about half of all fatal traffic accidents. It is particularly important that women who are pregnant avoid alcohol. Drinking while pregnant can lead to miscarriages, stillbirths, or fetal alcohol syndrome. “It is also important to remember that the typical alcoholic beverage has between 100 and 350 calories (and some cocktails can have more).” says Lichtenstein. “This is another issue that needs to be factored into decisions about whether to consume alcohol, how much, and how frequently.”
“Given the current state of the evidence, if you consume alcohol in moderation and have no contraindications, it is fine to continue,” says Lichtenstein. “However, if you do not currently consume alcohol it is not recommended you start as a way to lower your heart disease risk. There are many other things that can be done to improve health, including achieving and maintaining a healthy body weight, attaining recommended blood pressure levels and blood glucose concentrations, improving diet quality, avoiding exposure to tobacco products, controlling stress, and getting adequate sleep.