Source: www.forcon.ca

Alcohol absorption, distribution and elimination are simultaneous processes that commence upon consumption.

Absorption is the passage of alcohol into the blood. Distribution is the temporary placement of alcohol into various body tissues. Elimination is the removal of alcohol from the body. Diffusion is the method of passage of alcohol through cell membranes and is governed by concentration differences on either side of the cell wall.

Use the Blood Alcohol Calculator to estimate your blood alcohol level at a given time.

Blood alcohol concentration

A blood alcohol concentration (BAC) or blood alcohol level (BAL) reflects the amount of alcohol in the body. Food, type and quantity of beverage, weight, sex, and rate of elimination determine the BAC after the consumption of alcohol. The BAC is a measure of the difference between the rates of absorption and elimination. The change in BAC with time may be described graphically as a "blood alcohol curve," where the absorption phase is represented by a rising line and the elimination phase by a falling line.

Alcohol absorption

Alcohol is absorbed from the stomach and small intestine by diffusion. Most absorption occurs from the small intestine due to its large surface area and rich blood supply. The rate of absorption varies with the emptying time of the stomach. Generally, the higher the alcohol concentration of the beverage, the faster the rate of absorption. However, above a certain concentration, the rate of absorption may decrease due to the delayed passage of alcohol from the stomach into the small intestine.

The maximum absorption rate is obtained with the consumption of an alcoholic beverage containing approximately 20-25% (by volume or v/v) alcohol solution on an empty stomach. The absorption rate may be less when alcohol is consumed with food or when a 40% (v/v) alcohol solution is consumed on an empty stomach. The rate may also slow down when high fluid volume/low alcohol content beverages, such as beer, are consumed.

Normal social drinking

For normal social-type drinking, the highest BAC is usually achieved within 30 minutes after completion of consumption, though it could take as long as 60 minutes. When large amounts of alcohol are consumed over a short time interval, or when a large quantity of food is eaten with the alcohol, the absorption phase may not be complete for up to two (2) hours after last consumption.

Two-hour BAC plateau

In other situations, a subject may develop a plateau, where the blood alcohol level does not change for up to two hours. When this occurs the rate of absorption is equal to the rate of elimination and hence the blood alcohol concentration does not change. After two hours, the rate of elimination will exceed the rate of absorption and the blood alcohol level will begin to decrease.

Once in the blood, alcohol is carried throughout the body. The alcohol diffuses into tissues and fluids according to their water content. During the absorption phase, the BAC of arterial blood is greater than the BAC of venous blood. Arteries carry blood to a tissue, and veins remove blood from the tissue. At equilibrium, where the tissue has absorbed a proportionate quantity of alcohol, the BAC of arterial blood is equal to the BAC of venous blood.

Weight and sex affect BAC

A person's weight and sex determine the total volume of body water and consequently the BAC obtained upon consumption of a particular quantity of alcohol. Generally, the more a person weighs, the larger the volume of body water and the lower the BAC obtained from the consumption of a given amount of alcohol.

A female may have more fat tissue than a male of the same weight and therefore a smaller volume of body water. As a result, a female may obtain a slightly higher BAC upon consumption of the same quantity of alcohol as a male, all other factors being equal.

As the BAC decreases, alcohol diffuses from the tissues back into the blood.

Elimination of alcohol

Alcohol is eliminated from the body by excretion and metabolism. Most alcohol is metabolized, or burned, in a manner similar to food, yielding carbon dioxide and water. A small portion of alcohol is excreted, such as through the breath, leaving the body as alcohol, unchanged. It is this latter process that allows for breath alcohol testing.

Average rate of elimination