Alcohol and human health
Alcohol and human health

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Alcohol and human health

1.2.3 Chemical factors

Ethanol metabolites

The suggestion that acetaldehyde accumulation is involved in hangovers is largely due to the observation that high concentrations of acetaldehyde in the blood give rise to toxic effects which resemble hangovers (rapid pulse, sweating, nausea, etc.).

SAQ 5

Why would acetaldehyde accumulate in the body after heavy drinking?

Answer

Ethanol is converted into acetaldehyde by the enzyme ADH, and then ALDH catalyses the breakdown of acetaldehyde into acetic acid. If the first reaction occurs at a faster rate than the second, then acetaldehyde accumulates.

However, high concentrations of acetaldehyde in the blood are not detected during hangovers in most people, so there is no direct evidence that acetaldehyde is the root cause.

Other chemicals

Studies have shown that purer drinks (such as vodka and gin) cause fewer hangover symptoms than drinks rich in congeners (whisky, brandy, red wine). Congeners are the chemicals that provide characteristic taste, aroma and colour. However, pure ethanol can cause hangovers, so congeners can only be a contributing factor. One chemical that has been identified as potentially important in hangover is methanol.

Methanol is absorbed and metabolised by the same mechanisms as ethanol, but ethanol is preferentially metabolised when both substances are present. Methanol levels in the blood therefore remain high after ethanol levels decrease, possibly explaining the delayed onset of hangover (Jones, 1987). The products of methanol breakdown are formaldehyde and formic acid, both of which are very toxic: high concentrations can cause blindness and death. Drinks which are associated with increased hangover symptoms contain high levels of methanol (e.g. brandy, whisky).

Methanol poisoning is treated by administering large doses of ethanol; the methanol is thus metabolised more slowly, preventing the build-up of toxic formaldehyde and formic acid. This approach might form the basis for theories that consuming more alcohol is a way to overcome a hangover.

Hangover treatments

There are numerous treatments reputed to alleviate the symptoms of hangover, ranging from anecdotal folklore to costly pharmaceutical products. Hangover symptoms abate with time, but vary widely between individuals and occasions, so trials of remedies are of limited reliability. Whilst these remedies may not have been subject to systematic scientific testing, some are reasonable approaches based on what is understood about hangover physiology:

  • Consumption of food containing the sugar fructose, such as fruit or fruit juices, or bland food rich in carbohydrates, may help to counter symptoms arising from low blood sugar.

  • Sleeping is likely to relieve symptoms associated with fatigue.

  • Drinking copious volumes of water reduces dehydration.

  • Anti-inflammatory drugs, such as aspirin, are commonly used to relieve the symptoms of headache, but there is a risk that since they can irritate the gut lining they might compound alcohol-induced stomach disturbances.

  • Caffeine is traditionally widely used and may counteract fatigue symptoms.

  • More alcohol (Box 3) may alleviate mild withdrawal symptoms, and/or allow methanol time to clear the system without producing high concentrations of formaldehyde and formic acid. However, any immediate relief would be overshadowed by the reinitiation of the whole process.

Box 3 (Enrichment) ‘Hair of the dog’

This phrase is used to describe the consumption of a small alcoholic drink in order to cure hangover. The expression alludes to an old belief that an antidote to having been bitten by a mad dog was to place some burnt hair from the same dog onto the wound. The phrase is also used in Hungary ‘kutya harapást szörével’ translated as (you may cure) ‘the dog's bite with its fur’.

Phrases to describe the concept of drinking to alleviate hangover symptoms are also found elsewhere, such as the French ‘rallumer la chaudière’ (re-light the boiler) or the Danish ‘rejse sig ved det træ, hvor man er faldet’ (you should get up next to the tree where you fell).

A recent study concluded that ‘no compelling evidence exists to suggest that any complementary or conventional intervention is effective for treating or preventing the alcohol hangover’ and suggested that an effective intervention would remain elusive until the underlying biology was better understood (Pittler et al., 2005). Hangovers are unpleasant experiences that cause disruption to people's lives and can impair their ability to perform tasks such as working or driving effectively. The most effective way of reducing hangover symptoms is to avoid drinking excessive amounts of alcohol, especially drinks containing the highest levels of congeners.

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