Source: Lecture 21 | Biology, University of Michigan
Difficulty: Introductory. No specific prerequisites.
Alcohol (ethanol) acts as a central nervous system depressant and is metabolised primarily in the liver through a two-step enzyme pathway (ADH and ALDH). The liver can process only about one ounce of alcohol per hour, so excess intake accumulates in the blood and raises BAC. Binge and heavy drinking carry serious health risks including liver damage, cancers, and fetal alcohol syndrome, and no level of alcohol intake is associated with reduced cancer risk.
Ethanol
The intoxicating ingredient in beer, wine, and liquor. Acts as a central nervous system depressant. Energy content: 7 kcal per gram. In simple terms, this is what people mean when they say "alcohol."
Standard alcoholic drink
14 grams (0.6 fluid ounces) of pure alcohol. Equivalents: 12 ounces of 5% beer, 5 ounces of 12% wine, or 1.5 ounces of 40% (80 proof) liquor. Note: craft beers are often higher in alcohol percentage.
BAC (blood alcohol concentration)
The amount of alcohol present in the blood, measured in the breath or urine. The legal limit for intoxication in the US is 0.08% for drivers aged 21 and older.
ADH (alcohol dehydrogenase)
The enzyme that converts ethanol to acetaldehyde in the first step of alcohol metabolism.
ALDH (aldehyde dehydrogenase)
The enzyme that converts acetaldehyde to acetate in the second step of alcohol metabolism. Located in the mitochondria.
Acetaldehyde
A highly toxic intermediate of alcohol metabolism. Causes many of the ill effects of alcohol consumption and interferes with DNA synthesis and DNA repair.
Binge drinking
Consuming 4 (women) or 5 (men) standard drinks in less than 2 hours.
Heavy drinking
15 or more drinks per week for men; 8 or more drinks per week for women.
Moderate alcohol consumption
Up to 1 standard drink per day for women; up to 2 standard drinks per day for men.
Fetal alcohol syndrome (FAS)
A range of developmental, cognitive, and behavioural problems caused by drinking during pregnancy. Brain damage to the fetus can appear at any time during childhood. Individuals with FAS often have difficulty with coordination, emotional control, school work, socialisation, and holding a job.
2016 Surgeon General's report: alcohol and drug misuse are among America's most pressing public health concerns
Nearly 21 million Americans suffer from substance use disorders, more than those who have had all cancers combined
NIAAA: abusive college drinking is a significant public health problem
Ethanol enters the body through the stomach (20% absorbed immediately) and small intestine (80% absorbed)
Food in the stomach slows alcohol absorption
The stomach metabolises a small amount; the majority is metabolised in the liver
Pathway: Ethanol --(ADH)--> Acetaldehyde --(ALDH)--> Acetate --> CO2 + H2O
Acetaldehyde is highly toxic and interferes with DNA synthesis and repair
Acetate goes through cellular respiration
The liver can metabolise only about one ounce of alcohol per hour
Women have lower body water content, causing blood alcohol concentrations to increase more quickly than in men of the same body weight
Gender
Body weight and composition
Food intake before and during drinking
Use of other drugs or medications
Genes
People should not consume alcohol, or do so in moderation
No safe intake of alcohol is associated with reduced cancer risk
Perceived health benefits of moderate drinking on CVD may be related to other lifestyle characteristics, not the alcohol itself
Alcohol abuse and binge drinking increase violent crimes, drowning, and injuries from falls and vehicle crashes
Binge: 4 drinks (women) or 5 drinks (men) in less than 2 hours
Heavy: 8+ drinks per week (women) or 15+ drinks per week (men)
Brain: dementia, stroke, shrinkage of brain tissue, depression, anxiety, suicide
Oral cavity, throat, oesophagus: cancer
Cardiovascular: heart attack, cardiomyopathy, arrhythmia, hypertension
Breast: cancer (in women)
Liver: cirrhosis, cancer
Stomach: gastritis
Pancreas: pancreatitis
Colon: cancer
Reproductive: ovarian cancer, miscarriage, stillbirth (women); erectile dysfunction (men)
Bones: osteoporosis
Peripheral nervous system: numbness, pins and needles, muscle weakness
Immune system: suppressed function, increased risk of infectious disease
Drinking during pregnancy can cause brain damage to the fetus
Problems may appear at any time during childhood
Affected individuals often struggle with: coordination, emotional control, school work, socialisation, holding a job
Students sometimes assume moderate alcohol consumption is protective against cancer. No safe intake level is associated with reduced cancer risk.
Students may think the health benefits of moderate drinking on heart disease are well established. Current guidelines note that perceived CVD benefits may be related to other lifestyle characteristics.
Students sometimes believe the body can process alcohol quickly. The liver metabolises only about one ounce per hour.
⚠️ Know the standard drink equivalents: 12 oz beer (5%), 5 oz wine (12%), 1.5 oz liquor (40%/80 proof).
⚠️ Alcohol metabolism pathway: Ethanol --> Acetaldehyde (via ADH) --> Acetate (via ALDH). Acetaldehyde is the toxic intermediate.
⚠️ BAC legal limit: 0.08% for drivers aged 21+.
⚠️ Binge drinking: 4 drinks (women) / 5 drinks (men) in under 2 hours.
⚠️ The liver can only metabolise about one ounce of alcohol per hour.
⚠️ No safe level of alcohol consumption reduces cancer risk.
⚠️ Ethanol has an energy content of 7 kcal/g.
Fill in the blank: A standard alcoholic drink contains _____ grams of pure alcohol. (14)
True or False: The liver can metabolise several ounces of alcohol per hour. (False, only about one ounce)
Fill in the blank: The toxic intermediate in alcohol metabolism is _________. (acetaldehyde)
True or False: Moderate alcohol consumption is associated with reduced cancer risk. (False)
Fill in the blank: Ethanol provides _____ kcal per gram. (7)
Q: What constitutes binge drinking for men and women?
A: 5 standard drinks for men or 4 standard drinks for women in less than 2 hours.
Q: Describe the two-step metabolic pathway for alcohol in the liver.
A: Ethanol is converted to acetaldehyde by alcohol dehydrogenase (ADH), then acetaldehyde is converted to acetate by aldehyde dehydrogenase (ALDH) in the mitochondria. Acetaldehyde is highly toxic and interferes with DNA synthesis and repair.
Q: Why do women typically reach higher blood alcohol concentrations than men of the same weight after drinking the same amount?
A: Women have lower body water content, so the alcohol is distributed in a smaller volume of water, resulting in higher concentrations.
Q: Name three long-term health effects of heavy alcohol use.
A: Liver cirrhosis, cancer (oral, oesophageal, breast, colon), cardiomyopathy, pancreatitis, dementia, osteoporosis (any three).
Alcohol metabolism relies on the same mitochondrial processes discussed in Lecture 17 (Exercise and Health) under the aerobic energy system. The liver's role in detoxification connects to Lecture 16 (Dietary Supplements), where the liver's capacity to handle toxins was contrasted with unproven colon cleanse products. Fetal alcohol syndrome relates to Lecture 20's broader discussion of how developmental factors and nutrition affect health outcomes.
Alcohol, ethanol, BAC, blood alcohol concentration, ADH, alcohol dehydrogenase, ALDH, aldehyde dehydrogenase, acetaldehyde, acetate, standard drink, binge drinking, heavy drinking, moderate drinking, fetal alcohol syndrome, FAS, liver metabolism, cirrhosis, CNS depressant, NIAAA, dietary guidelines alcohol, craft beer alcohol content, alcohol and cancer, alcohol intoxication factors