It is a common and often frustrating experience to find that a few drinks affect you differently than they once did, causing intoxication to set in faster or hangovers to feel significantly worse. This change in alcohol tolerance is rooted in fundamental shifts in the body’s physiology. The way the body absorbs, distributes, and chemically processes alcohol changes over time, altering the amount of alcohol that reaches the brain and how long it remains in the system.
Shifts in Body Composition Over Time
One primary reason alcohol affects a person more intensely relates to the gradual changes in body composition that occur with age. Alcohol is a water-soluble molecule, meaning it distributes easily into the water content of the body, predominantly found in lean tissues like muscle. As people age, the total percentage of body water naturally decreases.
The body tends to lose lean muscle mass while the percentage of body fat often increases, even if overall body weight remains stable. Since fat tissue contains very little water compared to muscle, it does not absorb or dilute the alcohol effectively. This shift results in the same amount of alcohol being dispersed into a smaller volume of water.
Consequently, the concentration of alcohol in the bloodstream (Blood Alcohol Content or BAC) rises more quickly and reaches a higher peak than it would have previously. For instance, the total body water in men can decrease from about 60% of body weight to 57% by age 61. This reduction in the “dilution tank” means that one drink can produce effects similar to what two or three drinks did years earlier.
Declining Efficiency of Alcohol Metabolism
Beyond distribution, the body’s ability to break down alcohol chemically also becomes less efficient, primarily due to changes in liver function. The liver metabolizes over 90% of ingested alcohol in a two-step process involving specific enzymes. First, Alcohol Dehydrogenase (ADH) converts ethanol into a highly toxic compound called acetaldehyde.
The next step relies on Aldehyde Dehydrogenase (ALDH), which converts acetaldehyde into harmless acetate that the body can eliminate. As a person gets older, the overall activity of these enzymes, particularly ALDH, can diminish. This reduction in efficiency slows the entire metabolic process, meaning the alcohol and the toxic acetaldehyde remain in the system for longer periods.
The buildup of acetaldehyde is largely responsible for the unpleasant physical effects of a hangover, including nausea, headache, and flushing. When the liver’s capacity to process this toxin declines, the duration and severity of these hangover symptoms increase dramatically. The liver’s ability to break down alcohol can also be compromised by underlying health conditions or the long-term stress of regular consumption.
The Acute Impact of Health and Lifestyle Factors
Factors related to health status and daily habits can acutely interfere with the body’s tolerance to alcohol, separate from long-term composition or enzyme changes. A primary concern is the interaction between alcohol and prescription medications, which is more common as people age. Many common drugs, including antidepressants, high blood pressure medications, and sedatives, are processed by the liver’s enzyme systems.
When alcohol is introduced, it competes with these medications for the same metabolic pathways, slowing the breakdown of both substances. Combining alcohol with central nervous system depressants, even in small amounts, can amplify effects like dizziness, confusion, and drowsiness. These acute interactions make the intoxicating effects of alcohol feel much stronger and last longer.
Poor sleep quality and chronic stress also temporarily lower alcohol tolerance. Alcohol itself disrupts sleep by suppressing deep sleep and increasing awakenings. Entering a drinking session already sleep-deprived intensifies alcohol’s sedative effects, causing impairment more quickly. Furthermore, a decline in drinking frequency, a common lifestyle change, contributes to lower functional tolerance because the body is less accustomed to the acute effects of alcohol.