The chemistry of alcohol absorption, distribution, and elimination is complex and it varies from person to person. Much of the variability is due to genetic and environmental factors such as gender, body composition, food consumption, liver volume, genetics, and ethnicity. Some of the variability is due to the nature of the alcohol consumed.
For example, the degree and speed of absorption of alcohol from the small intestine can depend on time of day, drinking pattern, dosage form, concentration of alcohol in the beverage, and the existence of food in the stomach.
The amount and type of food present in the digestive tract has the most direct and measurable effect upon the rate of alcohol absorption.
Alcohol consumed on an empty stomach is absorbed by most people within 15 minutes to 2.5 hours. If alcohol is consumed with a moderate amount of food, the range typically increases from 30 minutes to 3.0 hours. On a full stomach, ranges from 3 to 6 hours have been reported.
Stomach emptying time is a key factor in the absorption time of alcohol. Any substance in the stomach can act like a sponge and delay alcohol’s movement into the small intestine, where the vast majority of absorption takes place. Food delays the stomach emptying time of alcohol, and decreases the availability of alcohol in the blood stream. See Graph 2. Thus, the amount of alcohol that reaches the duodenum and the liver is highly variable.
The net effect on the representative BA curve is a decreased area under the blood alcohol concentration curve, a lower peak concentration, and an increased time to reach peak.
Peak BAC is lower with food in the stomach than without food. Since the maximum concentration reached is less, a person who has the lower peak alcohol level takes a shorter time to clear the alcohol from the body than one who has a higher peak level. Consumption of alcohol with food can increase alcohol clearance by 1 to 2 hours, and increase the rate of alcohol metabolism by between 36% and 50%, as compared to consumption on an empty stomach.
Although food changes the shape of the BA curve, it is difficult to predict the exact effect of a given meal consumed by a given individual. The type of food consumed appears to have an effect as well.
Some scientists contend that the speed with which alcohol is consumed plays an important role in alcohol peak levels and times. Large amounts of alcohol, taken all at once may cause the pyloric valve to seize, delaying absorption. Conversely, if alcohol is consumed over a long period of time, the liver has a greater opportunity to eliminate what is being absorbed, so that there is a lower blood alcohol level (BAL) per unit of time.
Social drinking often results in the consumption of alcohol over an extended period of time. Some studies have shown that drinking in this manner may result in a faster absorption time.
Often drawn out consumption and rapid consumption both occur. A person may consume alcohol over a period of time, and then quickly consume one or two drinks just before leaving a drinking establishment. In these circumstances, the alcohol curve will increase and rise as to those last drinks.
Any substance that slows stomach emptying slows down absorption of alcohol that is consumed near the time of a meal. Cigarette smoking during or close in time to a meal has been found to slow stomach emptying and increase the time to reach maximum absorption.
The absorption of alcohol is not the same for all kinds of liquor. Alcohol higher in concentration can have an adverse affect on the pyloric valve, located between the stomach and small intestine. High concentrations of alcohol can cause the pyloric valve to seize, and thereby delay stomach emptying by up to 2 to 3 hours. Conversely, some drinks can cause the pyloric valve to spasm. Mixed drinks are generally absorbed faster than neat spirits due to pyloric spasm.
Another factor that may play a part in the time to reach peak BAC is the dose of alcohol consumed. Low alcohol doses accelerate stomach emptying; high doses delay emptying and slow bowel motility. Thus, high doses of alcohol tend to delay and increase the peak BAC.
Drinks high in sugar have a delayed absorption rate in much the same way food delays absorption. For example sweet vermouth is absorbed slower than champagne. Champagne also is carbonated, which tends to increase the rate of the opening of the pyloric valve, and thus gastric emptying time.
After consuming comparable amounts of alcohol, women tend have higher blood alcohol concentrations than men. This fact has been found to be true because of the difference in size, weight, and body composition of the sexes, with women tending to have relatively more fat and less body water (blood and fluids) than men. The activity of the enzyme alcohol dehydrogenase that breaks down alcohol is apparently lower in women as well.
Any physical changes to the stomach and intestines have the potential for affecting the absorption of alcohol. Some of these changes are the result of a chronic disease, surgical intervention, or merely physiological changes due to stress, shock or fear.
Even chronic use of alcohol facilitates the development of gastritis (inflammation of the stomach lining). Gastritis and gastric ulcers can increase blood flow and motility in the gastrointestinal tract, while cancers and gastric fibrosis can delay stomach emptying.
Chronic alcohol abusers also appear to have an increased incidence of infection by Helicobacter pylori (H-pylori). H-pylori causes infections in the stomach and can also produce gastritis.
Stomach infections by Helicobacter pylori (H. pylori) have been shown to significantly reduce metabolism of alcohol. H. pylori infections can lead to gastric mucosal injury, which in turn decreases alcohol dehydrogenase activity.
Alcohol absorption is impaired during trauma (in part because of reduced gut blood flow). Trauma, shock and fear divert blood flow from the stomach and small intestine, and often decrease the motility of stomach contents.
Surgeries that change the stomach or intestinal configuration also disrupt normal absorption of alcohol. For example, gastric bypass surgery for morbid obesity reduces the size of the stomach and eliminates a portion of the proximal end of the small intestine. One study found that the maximum blood-alcohol concentration was about 15% higher in the gastric bypass patients as compared to the control group, and the time to reach peak absorption was only 10 minutes as compared to 30 minutes for the control group.
Body composition affects absorption and the final peak alcohol level. As the body ages, lean body mass and total volume of distribution tends to decrease. Thus, age can affect the peak alcohol level achieved after a drinking session.
The understanding of drug-alcohol interactions is important for the full evaluation of a DUI case.
The stomach lining contains alcohol dehydrogenase (ADH), the enzyme that metabolizes or break down alcohol. Consequently, some alcohol is metabolized while still in the stomach and never enters the blood stream. This phenomenon is known as “first-pass” metabolism. Normal, healthy individuals exhibit considerable variation in the amount of first-pass metabolism that occurs. For example, women and the elderly tend to have less enzyme activity than men and younger individuals.
Certain drugs have been shown to inhibit ADH action in the stomach reducing the amount of first-pass metabolism and resulting in alcohol levels that are higher than would be expected for a specific dose of alcohol. These drugs include ranitidine (Zantac) and cimetidine (Tagamet), both of which are used to treat heartburn, stomach ulcers, and gastroesophageal reflux disease (GERD). Also included are ibuprofen and aspirin.
Glycine (found in antacid tablets), glycylglycine and glycylglycylglycine (amino acids) and alanine (used as an antihypertensive medication) all suppress the rate of stomach emptying and thus alcohol absorption from the gastrointestinal tract.
Since stomach emptying is lowered, alcohol has more time to be metabolized in the stomach. As a result, blood alcohol levels are lowered with the use of these substances.
Erythromycin appears to promote faster emptying of alcohol from the stomach and slower movement of the alcohol through the intestine, which subsequently increases the total amount of alcohol absorbed as well as the rate of alcohol absorption.
The autonomic nervous system is a network of nerves distributed throughout the body. These nerves mediate the bodily functions that occur without conscious control. Some of these functions include the movement of the heart, internal organs, and smooth muscles. The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems, which in turn are commonly described by which neurotransmitter mediates the nerve pulses: acetylcholine or norepinephrine. The term “cholinergic” is used to describe the neurons that release acetylcholine, and “adrenergic’ is commonly used to describe the neurons that release norepinephrine.
Table 1 shows some of the changes that can occur in the stomach and intestine, depending on which system is triggered.
|Organ Effected||Adrenergic Response||Cholinergic Response|
|Stomach Acid Secretion||Inhibition||Stimulation|
The sympathetic nervous system is continuously working. When stimulated during fear and rage, blood flow is diverted from the skin and gastrointestinal tract to the skeletal muscle, to prepare the body for the “fight or flight” response. In the same manner, sympathetic drugs such as amphetamines, decrease blood flow to the gastrointestinal tract, thereby delaying alcohol absorption from the stomach and small intestine.
Parasympathetic drugs, such as opiates and nicotine, increase absorption. Parasympathetic drugs also decrease gastric motility and prolong gastric emptying time. Intestinal secretions are diminished, and digestion of food in the small intestine is delayed.