Alcohol and Health

Alcohol and Health

Ethanol, C₂H₅OH, also known as ethyl alcohol or grain alcohol, is the only common alcohol that humans are able to digest. Alcohol is readily absorbed by the body when consumed in an aqueous solution. All common alcoholic drinks are aqueous solutions of ethanol.

Alcohol absorption generally begins in the stomach, although most absorption takes place from the small intestine. Because alcohol is distributed to all body fluids (in proportion to the water content of that fluid), alcohol can be detected and quantitatively measured in the blood, urine, cerebrospinal fluid, and water vapor from the lungs. Drug testing for alcohol level relies on this fact.

Metabolism

Only about 2 percent of consumed alcohol is excreted unchanged by the lungs or kidneys. The rest is metabolized by the body through biological oxidation with the aid of the enzymes alcohol dehydrogenase and acetaldehyde dehydrogenase. These are induced enzymes (produced in response to need), and are found in larger quantities in heavy drinkers than in nondrinkers.

Alcohol dehydrogenase catalyzes the oxidation of ethyl alcohol to acetaldehyde. Acetaldehyde is moderately toxic and is believed to be a major cause of headaches and hangovers.

The second enzyme, acetaldehyde dehydrogenase, catalyzes the oxidation of acetaldehyde to acetate. A small amount of acetate enters the Krebs (cellular digestion) cycle, while other acetate molecules enter other energy-conversion pathways of the body. The remainder of the acetate is stored as long-chain fatty acids and is ultimately oxidized to form carbon dioxide and water.

Although some human variation exists, the body can metabolize only about one drink (1¼ fluid ounces [0.036 liters]) per hour. Because the oxidation reactions are enzyme-catalyzed, little can be done to speed up the reactions.

Alcohol is processed by the liver. However, excessive quantities of alcohol cannot be processed during a single pass through the liver. Thus, alcohol can have a direct effect on other parts of the body. Most tissue effects are a part of an intricate, interrelated series of events.

Physiological Effects

Alcohol is a vasodilator (the blood vessels dilate or enlarge). Chronically dilated veins are often associated with liver disease, and the "enlarged red nose" of the chronic alcoholic is usually the result of permanently dilated blood vessels. Dilation of the veins of the esophagus can lead to hematemesis (vomiting blood). Late-stage alcoholics have been known to drown in their own blood because of ruptured esophageal blood vessels.

Edema, the accumulation of tissue fluid, occurs with alcohol consumption because when the blood vessels expand, the proteins as well as the fluids within the capillaries leak into the interstitial space . This accumulation between the cells leads to tissue swelling. Because the fluid is not within the blood vessels, apparent dehydration exists. Jaundice (yellowing of the body tissues) is generally caused by excessive bilirubin (a normal body pigment) in the extracellular fluids, and may indicate liver disease.

Alcohol is a central nervous system (CNS) depressant, meaning that with alcohol the central nervous system is operating at decreased efficiency. Alcohol is also a depressant of all major systems of the body. High quantities of alcohol function as an anesthetic. Alcohol also depresses the psychological inhibition and thus may appear to be a stimulant. Because of this apparent stimulation of certain behaviors, psychologists call alcohol a biphasic drug. The combination of CNS depression and inhibition release leads to the symptoms of drunkenness. Drunkenness, a term for which there is no precise definition, varies with body size, metabolic rate, individual absorption, and individual tolerance.

Chronic Alcoholism

Prolonged use of alcohol can lead to compensatory mechanisms for the depressed normal nervous system activity. The nervous system tends to "work harder" to maintain equilibrium and therefore, upon withdrawal of alcohol, the nervous system may experience excessive excitement which may lead to convulsions, seizures, and ultimately delirium tremens (the DT's), a state of restlessness, disorientation, and hallucinations .

Mental impairment in chronic alcohol use is difficult to quantify because some impairment is reparable either by itself or by the construction of alternate nervous routes in the brain. Perhaps the most noticeable of the reparable impairments is personality loss.

Other physiological involvements include sleep apnea , decreased REM (restful) sleep, headaches, inhibition of testosterone synthesis, pancreatic inflammation, and electrolyte imbalance in the blood.

The major nutritional problem with alcohol is poor diet. Also, excessive alcohol ingestion often leads to gastrointestinal irritation, and this can lead to ulcers, colitis (inflamed colon), and other chronic ailments.

It is estimated that about 10 percent of the human population is addicted to alcohol. Probably no single cause of alcohol addiction exists. Certain genetic markers have been discovered, and the genetic component of alcoholism is well documented. Nevertheless, genetics alone does not explain all alcohol addiction. Psychological components to alcohol addiction have also been identified. For most alcohol addicts, the only treatment is total abstinence from alcohol and participation in a program such as Alcoholics Anonymous. The alcoholic's body does not "forget" alcohol, and the induced enzymes mentioned earlier remain ready to continue their metabolic actions if alcohol use resumes.

see also Digestive System; Drug Testing; Krebs Cycle; Liver

Roberta M. Meehan

Bibliography

Alcoholics Anonymous. <www.alcoholics.anonymous.org>.

Blum, K. and J. E. Payne. Alcohol and the Addictive Brain. New York: The Free Press, 1991.

National Institute of Alcohol Abuse and Alcoholism. <www.niaaa.gov/>.