1.2.1 Physical disturbances
How can drinking alcohol result in dehydration?
Ethanol inhibits the release of vasopressin; this results in an increase in the volume of urine produced by the kidneys and can lead to dehydration.
Although vasopressin levels return to normal during hangover, once ethanol is no longer present in the blood, additional fluid loss may occur due to sweating, vomiting and diarrhoea. Symptoms of dehydration include many of those associated with hangovers (dizziness, light-headedness, weakness, thirst, etc.).
At a high concentration, ethanol damages cells on contact (Box 2) and so can cause irritation of the stomach and intestinal lining resulting in inflammation.
Ethanol also increases the production of gastric acid and intestinal secretions, and the after-effects of these processes include abdominal pain, nausea and vomiting, all of which can be associated with hangovers.
Box 2 (Enrichment) The antibacterial action of ethanol
Ethanol can act as a disinfectant because it damages cells it is in contact with. It is an effective disinfectant and is used at 70 per cent vol. strength in hospital swabs and laboratories to kill bacteria.
In previous centuries, weak beers and ciders were often brewed by, or given as a ration to, the peasant workforce, and were the drink of choice. Because of the antibacterial action of the ethanol, they were safer to drink than the often-contaminated water.
Low blood sugar
The level of glucose which is present in the blood is carefully maintained in order to ensure that cells receive a continuous supply of fuel for metabolic processes. Excess glucose from the diet is stored in the liver and released in a carefully regulated manner to maintain the level in the circulation. Ethanol consumed in large amounts disrupts this balance and this can result in low blood sugar levels a few hours later. Since glucose is the primary source of energy for cells in the brain, this could explain hangover symptoms such as fatigue, weakness, and mood disturbances.