Alcohol tolerance refers to the bodily responses to the functional effects of

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

. This includes direct tolerance, speed of recovery from insobriety and resistance to the development of

alcohol use disorder Alcoholism is the continued drinking of alcohol despite it causing problems. Some definitions require evidence of dependence and withdrawal. Problematic use of alcohol has been mentioned in the earliest historical records. The World Hea ...

Consumption-induced tolerance

Alcohol tolerance is increased by regular drinking. This reduced sensitivity to the physical effects of

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

consumption requires that higher quantities of alcohol be consumed in order to achieve the same

effects Effect may refer to: * A result or change of something ** List of effects ** Cause and effect, an idiom describing causality Pharmacy and pharmacology * Drug effect, a change resulting from the administration of a drug ** Therapeutic effect, ...

as before tolerance was established. Alcohol tolerance may lead to (or be a sign of) alcohol dependence. 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. Studies have shown that 2–3 weeks of daily alcohol consumption increases tolerance.

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. The alcohol tolerance is also connected with activity of ''

alcohol dehydrogenase Alcohol dehydrogenases (ADH) () are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+) to N ...

s'' (a group of

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s responsible for the breakdown of alcohol) in the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

, and in the bloodstream. High level of alcohol dehydrogenase activity results in fast transformation of ethanol to more toxic

acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic compound, organic chemical compound with the chemical formula, formula , sometimes abbreviated as . It is a colorless liquid or gas, boiling near room temperature. It is one of the most ...

. Such atypical alcohol dehydrogenase levels are less frequent in alcoholics than in non-alcoholics. Furthermore, among alcoholics, the carriers of this atypical enzyme consume lower ethanol doses, compared to the individuals without the

allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...

. 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. A mild flushing reaction occurs when the body metabolizes alcohol more quickly into acetaldehyde, a toxic metabolite. A more severe flushing reaction occurs when the body metabolizes the acetaldehyde more slowly, generally due to an inactive aldehyde dehydrogenase enzyme. Both of those conditions—faster conversion of alcohol to acetaldehyde and slower removal of acetaldehyde—reduce the risk for excessive drinking and alcohol dependence.

Alcohol tolerance in different ethnic groups

To engage in alcohol consumption and the development of an alcohol use disorder appear to be common to

primates Primates is an order of mammals, which is further divided into the strepsirrhines, which include lemurs, galagos, and lorisids; and the haplorhines, which include tarsiers and simians ( monkeys and apes). Primates arose 74–63 ...

, and is not a specific human phenomenon. Humans have access to alcohol in far greater quantity than non-human primates, and the availability increased, particularly with the development of agriculture. The tolerance to alcohol is not equally distributed throughout the world's population. Genetics of alcohol dehydrogenase indicate resistance has arisen independently in different cultures. In North America, Native Americans have the highest probability of developing an

compared to Europeans and Asians. Different alcohol tolerance also exists within Asian groups, such as between Chinese and Koreans. The health benefits of a modest alcohol consumption reported in people of European descent appear not to exist among people of African descent. Higher body masses and the prevalence of high levels of alcohol dehydrogenase in an individual increase alcohol tolerance, and both adult weight and enzymes vary with ethnicity. Not all differences in tolerance can be traced to biochemistry, however. Differences in tolerance levels are also influenced by socio-economic and cultural difference including diet, average body weight and patterns of consumption.

In animals

Ethanol is nutritious but highly intoxicating for most animals, which typically tolerate only up to 4% in their diet. However, a 2024 study found that

oriental hornet The Oriental hornet (''Vespa orientalis'') is a social insect species of the family Vespidae. It can be found in Southwest Asia, Northeast Africa, the island of Madagascar (but no reports have been made of its presence on the island for many year ...

s fed sugary solutions containing 1% to 80% ethanol for a week showed no adverse effects on behavior or lifespan.

Footnotes

References