Multiple research studies have found that the brains of people with severe alcohol use disorder are smaller and lighter than the brains of those who do not have this condition.1 This alcohol-linked brain shrinkage affects the networks that regions of the brain use to communicate with other regions. The parts of the brain that allow neurons to communicate with neighboring neurons are also affected.
Some Damage Is Reversible
Although chronic alcohol misuse causes significant brain damage, abstinence can reverse some (but not all) damage.2 With appropriate interventions, people with alcohol use disorder can attain long-term sobriety despite deficits in decision-making related to brain shrinkage.3
How Alcohol Causes Brain Shrinkage
The gray matter in the cerebral cortex controls most of the brain’s complex mental functions. The cortex is filled with neurons that connect by fibers to different regions of the brain and to other neurons inside the brain and spinal cord. The nerve fibers are the white matter of the brain—the “hard-wiring.”
These nerve fibers have numerous shorter fibers called dendrites that branch out like the roots of a tree to allow the neurons to “talk” with other neurons. A neuron can communicate with as few as five or as many as 10,000 other neurons at a time.
These two parts of the brain—the white matter and the dendrites—are most vulnerable to the shrinkage that alcohol misuse can cause.
Brain shrinkage is not the only way alcohol misuse can damage the brain. Alcohol can also cause chemical changes that affect the function of neurotransmitters (chemical messengers that carry signals between the brain to the rest of the body).4
How Alcohol Affects the Brain
Chronic alcohol misuse creates complex, toxic metabolic and nutritional interactions that can cause mental deficits. Some of these are still not understood completely.
- Acetaldehyde, a chemical that is produced when alcohol is metabolized, could cause toxic effects.
- Malnutrition, especially thiamine deficiency, could play a role.
- Cirrhosis of the liver can also cause brain damage.
- Head injury and sleep apnea can contribute to brain damage.5
Alcohol, thiamine deficiency, and cirrhosis are linked. Some researchers believe they contribute in a complex manner to brain damage.6
Is Brain Shrinkage Permanent?
Some of the brain damage caused by alcohol can be reversed if a person stops drinking and maintains a period of abstinence. But some of it is permanent and cannot be undone.
The most significant permanent damage caused by alcohol is nerve cell loss. Some nerve cells cannot be replaced once they are lost, including those in the frontal cortex, cerebellum, and other regions deep inside the brain.7
However, abstinence can help reverse the shrinkage of dendrites. Studies show they will begin to grow again after weeks or months of abstinence.8 Once this happens, brain function may improve.
Some of the brain damage caused by cirrhosis of the liver can begin to reverse with treatment.9 Brain damage due to thiamine deficiency in people who misuse alcohol can easily be treated with thiamine supplements, but repeated deficiencies can cause permanent damage.
Impact of Brain Shrinkage Caused by Alcohol Use
One reason that people with alcohol use disorder are so prone to relapse is the damage alcohol causes to the brain’s reward system and decision-making abilities. The result is that the person is more motivated by immediate rewards than delayed ones. Addictive substances such as alcohol provide immediate intoxicating rewards.
Chronic alcohol misuse chemically changes the brain’s reward system to the point that the drinker’s pursuit of rewards becomes pathological.
Long-term, heavy alcohol consumption affects the brain’s frontal lobe functions, which include inhibition, decision-making, problem-solving, and judgment. This kind of brain damage makes it difficult to maintain long-term sobriety.
However, people with alcohol use disorder can overcome these challenges with abstinence, which helps reverse the damages. They then can achieve long-term, multi-year sobriety when motivated to do so.8
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