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Abbreviation for alcohol dehydrogenases. These are enzymes found in the human liver (and also in the digestive tract) which, in the presence of the co-enzyme NAD (nicotinamide adenine dinucleotide, which acts as a hydrogen carrier), breaks down alcohol and oxidises it to acetaldehyde. This is then detoxified to biologically activated acetic acid with the help of the enzyme ALDH (aldehyde dehydrogenase) and finally converted to carbon dioxide and water, which normally keeps the concentration of free acetaldehyde in the body very low. Among East Asians, the indigenous peoples of America (Indians) and the Aborigines of Australia, ALDH is inactive in about 80% of cases, therefore these ethnic groups tolerate only small amounts of alcohol. In Europeans, this alcohol intolerance occurs in only about 5% of the population

ADH are also present in yeasts; yeast ADH is used to determine blood alcohol content. There are two reasons why women tolerate less alcohol than men. On the one hand this is due to the lower body weight and the higher proportion of body fat. On the other hand, the female liver also has to break down sex hormones. When oestrogen levels drop during menopause, women can tolerate more alcohol. When larger amounts of the alcohol type methanol (wood alcohol) are broken down, the toxic formic acid can be formed. See further information or keywords on this topic under Health.

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