How Alcohol Metabolizes in the Liver
The liver breaks down 90-95% of ingested alcohol via two enzymes: alcohol dehydrogenase (ADH) converts ethanol to acetaldehyde, then aldehyde dehydrogenase (ALDH) turns acetaldehyde into acetate.[1] This process generates reactive oxygen species (ROS) and depletes antioxidants like glutathione, causing oxidative stress that damages liver cells.[2]
From Fatty Liver to Alcoholic Hepatitis
Daily heavy drinking (over 30g alcohol for men, 20g for women) leads to alcoholic fatty liver disease within weeks, where fat accumulates in hepatocytes due to disrupted fat metabolism and increased fatty acid uptake.[3] Progression to alcoholic hepatitis occurs with continued use: acetaldehyde forms protein adducts, triggering inflammation, neutrophil infiltration, and cell death (apoptosis/necrosis).[4] Symptoms include jaundice, fever, and abdominal pain.
Development of Cirrhosis and Fibrosis
Chronic exposure activates hepatic stellate cells, which produce collagen and scar tissue (fibrosis).[5] This replaces healthy tissue, forming nodules in cirrhosis—a point of no return where liver function fails. Portal hypertension follows, risking variceal bleeding and ascites.[6] About 10-20% of heavy drinkers reach cirrhosis after 10+ years.[7]
Role of Genetics and Amount Consumed
Genetic variants in ADH/ALDH affect acetaldehyde buildup; East Asians with ALDH2 deficiency experience rapid toxicity.[8] Risk escalates with dose: 40-80g/day triples cirrhosis odds; women are more vulnerable due to lower body mass and enzyme activity.[9] Binge drinking worsens acute injury via endotoxemia from gut bacteria.[10]
Why Some People Avoid Damage
Moderate drinkers (under 20g/day) rarely progress due to adaptive repair mechanisms, but any excess tips the balance toward injury. Co-factors like obesity, hepatitis C, or malnutrition accelerate damage by compounding oxidative stress and inflammation.[11]
[1] National Institute on Alcohol Abuse and Alcoholism (NIAAA), Alcohol Metabolism
[2] Cederbaum AI, World J Gastroenterol (2012)
[3] European Association for the Study of the Liver (EASL), J Hepatol (2018)
[4] Gao B & Bataller R, Gastroenterology (2011)
[5] Bataller R et al., J Clin Invest (2005)
[6] Tsochatzis EA et al., Lancet (2014)
[7] Bellentani S et al., Ann Intern Med (1997)
[8] Edenberg HJ, Alcohol Clin Exp Res (2007)
[9] Thun MJ et al., N Engl J Med (2002)
[10] Szabo G, Nat Rev Gastroenterol Hepatol (2015)
[11] American Association for the Study of Liver Diseases (AASLD), Hepatology (2021)