Alcohol and Alcoholism: Introduction

Alcohol, a drug, is consumed at some time by up to 80% of the population. At low doses alcohol can have some beneficial effects such as decreased rates of myocardial infarction, stroke, gallstones, and possibly vascular or Alzheimer's dementias, but the consumption of more than two standard drinks per day increases the risk for health problems in many organ systems. Heavy repetitive drinking, as is seen in alcohol abuse and dependence, cuts short the life span by an estimated decade in both genders, all cultural groups, and all socioeconomic strata. Even low doses of alcohol have a significant effect on many organ systems, adversely affecting most preexisting disease states and altering the effectiveness or blood levels of most over-the-counter and prescribed medications.

Pharmacology and Nutritional Impact of Ethanol

Ethanol is a weakly charged molecule that moves easily through cell membranes, rapidly equilibrating between blood and tissues. The level of alcohol in the blood is expressed as milligrams or grams of ethanol per deciliter (e.g., 100 mg/dL or 0.10 g/dL); a level of 0.02 to 0.03 results from the ingestion of one to two typical drinks. In round figures, 340 mL (12 oz) of beer, 115 mL (4 oz) of nonfortified wine, and 43 mL (1.5 oz) (a shot) of 80-proof beverage each contain 10 to 15 g of ethanol; 0.5 L (1 pint) of 86-proof beverage contains 160 g (about 16 standard drinks), and 1 L of wine contains 80 g of ethanol. Congeners found in alcoholic beverages, including low-molecular-weight alcohols (e.g., methanol and butanol), aldehydes, esters, histamine, phenols, tannins, iron, lead, and cobalt, may contribute to the adverse health consequences associated with heavy drinking.

Ethanol is a central nervous system (CNS) depressant that decreases neuronal activity, although some behavioral stimulation is observed at low blood levels. This drug has cross-tolerance with other depressants, including benzodiazepines and barbiturates, and all produce similar behavioral alterations. Alcohol is absorbed from mucous membranes of the mouth and esophagus (in small amounts), from the stomach and large bowel (in modest amounts), and from the proximal portion of the small intestine (the major site). The rate of absorption is increased by rapid gastric emptying; by the absence of proteins, fats, or carbohydrates (which interfere with absorption); by the absence of congeners; by dilution to a modest percentage of ethanol (maximum at about 20% by volume); and by carbonation (e.g., champagne).

Between 2% (at low blood alcohol concentrations) and 10% (at high blood alcohol concentrations) of ethanol is excreted directly through the lungs, urine, or sweat, but the greater part is metabolized to acetaldehyde, primarily in the liver. The most important pathway occurs in the cell cytosol where alcohol dehydrogenase (ADH) produces acetaldehyde, which is then rapidly destroyed by aldehyde dehydrogenase (ALDH) in the cytosol and mitochondria (). A second pathway in the microsomes of the smooth endoplasmic reticulum (the microsomal ethanol-oxidizing system, or MEOS), is responsible for 10% of ethanol oxidation at high blood alcohol concentrations. The metabolism of alcohol. javascript:windowReference('Reference',%20'popup.aspx?aID=109575');