8.2 – Alcohol and the Human Body

In moderation, alcohol is pleasant and relaxing, it may even, according to some research, be beneficial. One small glass of whiskey taken each day is said to help control arteriosclerosis but the benefits are lost if more is consumed.

Alcohol’s Properties

  • Alcohol is a general term denoting a family of organic chemicals with common properties. Members of this family include ethanol, methanol, isopropanol and others.
  • Alcohol (ethanol) is a clear, volatile liquid that burns (oxidizes) easily. It has a slight, characteristic odor and is very soluble in water. Alcohol is an organic compound composed of carbon, oxygen, and hydrogen. Its chemical formula is C2H5OH.
  • Alcohol is a central nervous system depressant. This body system is the most severely affected by alcohol. The degree of impairment to which the central nervous system function is directly proportional to the concentration of alcohol in the blood.

  • When ingested, alcohol passes from the stomach into the small intestine, where it is rapidly absorbed into the blood and distributed throughout the body. Because it is distributed so quickly and thoroughly, the alcohol can affect the central nervous system even in small concentrations. In low concentrations, alcohol reduces inhibitions. As blood alcohol concentration increases, a person’s response to stimuli decreases markedly, speech becomes slurred and he or she becomes unsteady and has trouble walking. With very high concentrations, greater than 0.35 grams/100 milliliters of blood, a person can become comatose and die.
  • The American Medical Association has defined the blood alcohol concentration level of impairment for all people to be 0.04 grams/100 milliliters of blood (equivalent to .04 grams/210 liters of breath).

Alcohol is absorbed from all parts of the gastrointestinal tract largely by simple diffusion into the blood. However the small intestine is by far the most efficient region of the gastrointestinal tract for alcohol absorption because of its very large surface area.

Alcohol has a high affinity for water and is therefore found in body tissues and fluids. Absorbed alcohol is rapidly carried throughout the body in the blood. Once absorption of alcohol is complete, equilibrium occurs in such a way that blood at all points in the system contains approximately the same concentration of alcohol.

The liver is responsible for the elimination, through metabolism, of 95% of ingested alcohol from the body. The remainder of the alcohol is eliminated through excretion of alcohol in breath, urine, sweat, feces, milk and saliva. Healthy people metabolize alcohol at a fairly consistent rate. As a rule of thumb, a person will eliminate one average drink or .5 oz (15 ml) of alcohol per hour. There are several factors that influence this rate.

  • The rate of elimination tends to be higher when the blood alcohol concentration in the body is very high.
  • Chronic alcoholics may (depending on liver health) metabolize alcohol at a significantly higher rate than the average.
  • The body’s ability to metabolize alcohol quickly tends to diminish with age.

Body Weight and Body Type
In general, the less you weigh the more you will be affected by a given amount of alcohol. Alcohol has a high affinity for water. So for two individuals with similar body compositions and different weights, the larger individual will achieve lower alcohol concentrations than the smaller one if ingesting the same amount of alcohol. However, for people of the same weight, a well-muscled individual will be less affected than someone with a higher percentage of fat since fatty tissue does not contain very much water and will not absorb very much alcohol.

Rate Of Consumption
Blood alcohol concentration depends on the amount of alcohol consumed and the rate at which the user’s body metabolizes alcohol. Because the body metabolizes alcohol at a fairly constant rate, ingesting alcohol at a rate higher than the rate of elimination results in a cumulative effect and an increasing blood alcohol concentration.

Alcohol Content
It is not the matter of how many drinks you have but how much alcohol you consume. Some drinks are more potent than others.

Alcohol Content of Some Typical Drinks

Drink Alcohol Content
Manhattan 1.15 oz. (34 ml)
Dry Martini 1.00 oz. (30 ml)
Malt liquor-12 oz. (355 ml) 0.71 oz. (21 ml)
Airline miniature 0.70 oz. (21 ml)
Whiskey Sour/Highball 0.60 oz. (18 ml)
Table Wine – 5 oz. (148 ml) 0.55 oz. (16 ml)
Beer – 12 oz. (355 ml) 0.54 oz. (16 ml)
Reduced Alcohol Beer 0.28 oz. (8 ml)

The concentration of the drinks that one ingests can have a slight effect on the peak alcohol concentration due to the differences in absorption rate of different concentrations of alcohol.

  • Alcohol is most rapidly absorbed when the concentration of the drink is between 10% and 30%.
  • Below 10%, the concentration gradient in the gastrointestinal tract is low.
  • On the other hand concentrations higher than 30% tend to irritate the mucous membranes of the gastrointestinal tract and the pyloric sphincter, causing increased secretion of mucous and delayed gastric emptying.

When food is taken along with alcohol, it results in a lower and delayed blood alcohol concentration peak (the point of greatest intoxication).

  • First, because alcohol is absorbed most efficiently in the small intestine, the ingestion of food can slow down the absorption of alcohol into one’s system.
  • Second and equally important is the fact that alcohol elimination rates are inversely proportional to alcohol concentration in the blood. Therefore, suppressed levels of alcohol due to food ingestion cause the body to eliminate the alcohol that is absorbed at a faster rate.


Alcohol effects could be increased if you are taking any medication. You should always consult your physician or the medical information that accompanies the medication. Be aware of the possible effects of alcohol when taken in conjunction with medication.


Fatigue causes many of the same symptoms that are caused by alcohol intoxication. These and other symptoms will be amplified if alcohol intoxication is concurrent with fatigue.


Tolerance is the reduction of the effectiveness of a drug after a period of prolonged or heavy use of that drug or a related drug (cross-tolerance). There are at least two types of tolerance that work with alcohol.

  • The first is metabolic tolerance in which the alcohol is metabolized at a higher rate (up to two times as quickly) in chronic users. Because of the higher metabolic rate for alcohol, chronic alcohol users compare to the average drinker achieve lower peak blood alcohol concentrations when the same amount of alcohol is ingested.
  • The second is functional tolerance in which there is an actual change in the organ or system’s sensitivity to the drug. Studies have shown that chronic alcohol users can have twice the tolerance for alcohol as an average person.

Gender Differences

  • In general, but by no means in all cases, women tend to have a higher percentage of body fat and thus a lower percentage of body water. Therefore, if a man and a woman of the same weight ingest the same amount of alcohol the woman will tend to achieve a higher alcohol concentration. This, of course, would not be true if the woman was very fit and the man was somewhat obese, but on average, this is the case.
  • Another gender-based difference is in the elimination of alcohol. Studies appear to show that women eliminate alcohol from their bodies at a rate 10% greater than that of men.


Total body water tends to decrease with age, so an older person will be more affected by effects of alcohol.

Related Courses