The long-term impact of alcohol on the brain encompasses a wide range of effects, varying by drinking patterns, age, genetics, and other health factors. Among the many organs alcohol affects, the brain is particularly vulnerable. Heavy drinking causes alcohol-related brain damage, with alcohol acting as a direct neurotoxin to nerve cells, while low levels of alcohol consumption can cause decreases in brain volume, regional gray matter volume, and white matter microstructure. Low-to-moderate alcohol intake may be associated with certain cognitive benefits or neuroprotection in older adults. Social and psychological factors can offer minor protective effects. The overall relationship between alcohol use and brain health is complex, reflecting the balance between alcohol's neurotoxic effects and potential modulatory influences.
Classification The neurological consequences of long-term alcohol use can be broadly classified into harmful outcomes (e.g., brain atrophy, cognitive decline, dementia), potential neutral effects, and, in limited cases, minor protective effects associated with low-to-moderate consumption. Severe manifestations are often categorized under alcohol-related brain damage (ARBD), including conditions such as Wernicke-Korsakoff syndrome and alcohol-related dementia.
Alcoholics can typically be divided into two categories, uncomplicated and complicated. Uncomplicated alcoholics do not have nutritional deficiency states or liver disease, but have a reduction in overall brain volume due to white matter cerebral atrophy. The severity of atrophy sustained from alcohol consumption is proportional to the rate and amount of alcohol consumed during a person's life. Complicated alcoholics may have liver damage that impacts brain structure and function and nutritional deficiencies "that can cause severe brain damage and dysfunction".
Characteristics
Excessive alcohol consumption is associated with widespread and significant brain lesions, specifically damage to brain regions including the frontal lobe, limbic system, and cerebellum, with widespread cerebral atrophy, or brain shrinkage caused by neuron degeneration. This damage can be seen on neuroimaging scans. Alcohol alters both the structure and function of the brain as a result of the direct neurotoxic effects of alcohol intoxication or acute alcohol withdrawal. Increased alcohol intake is associated with damage to brain regions including the frontal lobe, limbic system, and cerebellum, with widespread cerebral atrophy, or brain shrinkage caused by neuron degeneration. Frontal lobe damage becomes the most prominent as alcoholics age and can lead to impaired neuropsychological performance in areas such as problem solving, good judgment, and goal-directed behaviors. Impaired emotional processing results from damage to the limbic system. This may lead to troubles recognizing emotional facial expressions and "interpreting nonverbal emotional cues".
The effects can manifest much later—mid-life Alcohol Use Disorder has been found to correlate with increased risk of severe cognitive and memory deficits in later life.
Alcohol consumption can substantially impair neurobiologically-beneficial and -demanding exercise.
In some cases occasional moderate consumption may have ancillary benefits on the brain due to social and psychological benefits if compared to alcohol abstinence and soberness. Researchers have found that moderate alcohol consumption in older adults is associated with better cognition and well-being than abstinence.
Complications
Serious complications include irreversible brain damage, psychiatric disorders (e.g., depression, anxiety), and increased risk of other neurodegenerative conditions, such as Alzheimer's disease.
Causes
Alcohol is known to have direct neurotoxic effects on brain matter, both during alcohol intoxication and alcohol withdrawal. While the extent of causation is difficult to prove, alcohol intake – even at levels often considered to be low – "is negatively associated with global brain volume measures, regional gray matter volumes, and white matter microstructure" and these associations become stronger as alcohol intake increases. Available under CC BY 4.0.
Alcohol related brain damage is not only due to the direct toxic effects of alcohol; alcohol withdrawal, nutritional deficiency, electrolyte disturbances, and liver damage are also believed to contribute to alcohol-related brain damage.
Binge drinking
Binge drinking, or heavy episodic drinking, can lead to damage in the limbic system that occurs after a relatively short period of time. This brain damage increases the risk of alcohol-related dementia, and abnormalities in mood and cognitive abilities. Binge drinkers also have an increased risk of developing chronic alcoholism. Alcoholism is a chronic relapsing disorder that can include extended periods of abstinence followed by relapse to heavy drinking. It is also associated with many other health problems including memory disorders, high blood pressure, muscle weakness, heart problems, anaemia, low immune function, liver disease, disorders of the digestive system, and pancreatic problems. It has also been correlated with depression, unemployment, and family problems with an increased risk of domestic abuse.
It is unclear how the frequency and length of binge drinking sessions impacts brain damage in humans. Humans who drank at least 100 drinks (male) or 80 drinks (female) per month (concentrated to 21 occasions or less per month) throughout a three-year period had impaired decision-making skills compared to non-binge drinkers.
Thiamine deficiency
Thiamine is a vitamin the body needs for growth, development, and cellular function, as well as converting food into energy. Thiamine is naturally present in some foods, added to some food products, and available as a dietary supplement. A nutritional deficiency in thiamine can worsen alcohol-related brain damage. There is a genetic component to thiamine deficiency that causes intestinal malabsorption. A nutritional vitamin deficiency state that is caused by thiamine deficiency which is seen most commonly in alcoholics leads to Wernicke's encephalopathy and Alcoholic Korsakoff syndrome (AKS) which frequently occur simultaneously, known as Wernicke–Korsakoff syndrome (WKS). This disorder is preventable through supplementation of the diet by thiamine and an awareness by health professionals to treat 'at risk' patients with thiamine. Thiamine deficiency may occur in upwards of 80% of patients with alcoholism however, only ≈13% of such individuals develop WKS, raising the possibility that a genetic predisposition to WKS may exist in some individuals. Lesions, or brain abnormalities, are typically located in the diencephalon which result in anterograde and retrograde amnesia, or memory loss.
Mechanisms of action
Alcohol affects the brain through multiple mechanisms. The cerebral atrophy that alcoholics often present with is due to alcohol induced neurotoxicity. Evidence of neurodegeneration can be supported by an increased microglia density and expression of proinflammatory cytokines in the brain. Animal studies find that heavy and regular binge drinking causes neurodegeneration in corticolimbic brain regions areas which are involved in learning and spatial memory. The corticolimbic brain regions affected include the olfactory bulb, piriform cortex, perirhinal cortex, entorhinal cortex, and the hippocampal dentate gyrus. It was found that a heavy two-day drinking binge caused extensive neurodegeneration in the entorhinal cortex with resultant learning deficits in rats. Alcohol abuse affects neurons in the frontal cortex that typically have a large soma, or cell body. This type of neuron is more susceptible to Alzheimer's disease and normal aging. Research is still being conducted to determine whether there is a direct link between excessive alcohol consumption and Alzheimer's disease. The volume of the corpus callosum, a large white matter tract that connects the two cerebral hemispheres, is shown to decrease with alcohol abuse due to a loss of myelination. This integration between the two cerebral hemispheres and cognitive function is affected. A limited amount of myelin can be restored with alcohol abstinence, leading to transient neurological deficits.
The endocrine system includes the hypothalamic–pituitary–adrenal axis, the hypothalamic–pituitary–gonadal axis, the hypothalamic–pituitary–thyroid axis, the hypothalamic–pituitary–growth hormone/insulin-like growth factor-1 axis, and the hypothalamic–posterior pituitary axis, as well as other sources of hormones, such as the endocrine pancreas and endocrine adipose tissue. Alcohol abuse disrupts all of these systems and causes hormonal disturbances that may result in various disorders, such as stress intolerance, reproductive dysfunction, thyroid problems, immune abnormalities, and psychological and behavioral disorders.
Higher order functioning of the cerebral cortex is organized by the cerebellum. In those with cerebral atrophy, Purkinje cells, or the cerebellar output neurons, in the vermis are reduced in number by 43%. This large reduction in Purkinje cells causes a decrease in high order cerebral cortex organization. The cerebellum is also responsible for refining crude motor output from the primary motor cortex. When this refinement is missing, symptoms such as unsteadiness and ataxia will present. A potential cause of chronic alcoholic cerebellar dysfunction is an alteration of GABA-A receptor. This dysfunction causes an increase in the neurotransmitter GABA in cerebellar Purkinje cells, granule cells, and interneurons leading to a disruption in normal cell signaling.
An MRI brain scan found that levels of N-acetylaspartate (NAA), a metabolite biomarker for neural integrity, was lower in binge drinkers. Additionally, abnormal brain metabolism, a loss of white brain matter in the frontal lobe, and higher parietal gray matter NAA levels were found. This shows a correlation between binge drinking, poor executive functioning, and working memory. A decrease in frontal lobe NAA levels is associated with impaired executive functioning and processing speed in neuro-performance tests.
Neuroinflammation Ethanol can trigger the activation of astroglial cells which can produce a proinflammatory response in the brain. Ethanol interacts with the TLR4 and IL-1RI receptors on these cells to activate intracellular signal transduction pathways. Specifically, ethanol induces the phosphorylation of IL-1R-associated kinase (IRAK), ERK1/2, stress-activated protein kinase (SAPK)/JNK, and p38 mitogen-activated protein kinase (p38 MAPK). Activation of the IRAK/MAPK pathway leads to the stimulation of the transcription factors NF-kappaB and AP-1. These transcription factors cause the upregulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression. The upregulation of these inflammatory mediators by ethanol is also associated with an increase in caspase 3 activity and a corresponding increase in cell apoptosis. The exact mechanism by which various concentrations of ethanol either activates or inhibits TLR4/IL-1RI signaling is not currently known, though it may involve alterations in lipid raft clustering or cell adhesion complexes and actin cytoskeleton organization.
Changes in dopaminergic and glutamatergic signaling pathways