Alcohol tolerance refers to the bodily responses to the functional effects of ethanol in alcoholic beverages. This includes direct tolerance, speed of recovery from insobriety and resistance to the development of alcoholism.
Alcohol tolerance is increased by regular drinking. This reduced sensitivity requires that higher quantities of alcohol be consumed in order to achieve the same effects as before tolerance was established. Alcohol tolerance may lead to (or be a sign of) alcohol dependency.
Heavy alcohol consumption over a period of years can lead to "reverse tolerance". A liver can be damaged by chronic alcohol use, leading to a buildup of fat and scar tissue. The reduced ability of such a liver to metabolize or break down alcohol means that small amounts can lead to a high blood alcohol concentration (BAC) and more rapid intoxication.
Physiology of alcohol tolerance
Direct alcohol tolerance is largely dependent on body size. Large-bodied people will require more alcohol to reach insobriety than lightly built people. Thus, men, being larger than women on average, will have a higher alcohol tolerance on average. The alcohol tolerance is also connected with activity of alcohol dehydrogenases (a group of enzymes responsible for the breakdown of alcohol) in the liver, and in the bloodstream.
High level of alcohol dehydrogenase activity results in fast transformation of ethanol to more toxic acetaldehyde. Such atypical alcohol dehydrogenase levels are less frequent in alcoholics than in nonalcoholics and, alongside other symptoms, can indicate various forms of liver disease. Furthermore, among alcoholics, the carriers of this atypical enzyme consume lower ethanol doses, compared to the individuals without the allele.
Alcohol tolerance in different ethnic groups
The tolerance to alcohol is not equally distributed throughout the world's population, and genetics of alcohol dehydrogenase indicate resistance has arisen independently in different cultures. In North America, Native Americans have the highest probability of developing alcoholism compared to Europeans and Asians. The high legal drinking age has been cited as a causal factor for alcohol abuse.
Higher body masses and the prevalence of high levels of alcohol dehydrogenase in an individual increase alcohol tolerance. The high alcohol tolerance in Europeans has probably evolved as a consequence of centuries of exposure to alcohol in established agricultural societies.
Not all differences in tolerance can be traced to biochemistry. Differences in tolerance levels are also influenced by socio-economic and cultural difference including diet, average body weight and patterns of consumption.
An estimated one out of twenty people have an alcohol flush reaction. It is not in any way an indicator for the drunkenness of an individual. It is colloquially known as "Face Flush", a condition where the body metabolizes alcohol nearly 100-times more efficiently into acetaldehyde, a toxic metabolite. Flushing, or blushing, is associated with the erythema (reddening caused by dilation of capillaries) of the face, neck, and shoulder, after consumption of alcohol.
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