The symptoms of hangover
In the scientific literature, hangover is generally described as a malaise manifested by a constellation of biological, physiological and affective symptoms. These can be severe enough to impair function. The discomfort begins when blood alcohol content starts to drop and reaches a peak when it is back to zero. The unpleasantness associated with hangover rarely lasts more than 24 hours.
Hangover symptoms are associated with blood alcohol content, which is determined primarily by three things: time, weight and sex. The distribution of alcohol in the blood is influenced by the ratio of fat to lean tissue in the body, which explains why two people may weigh the same and drink the same amount but have different blood alcohol content. Age is also a factor. Hence, blood alcohol content calculations are approximate.
The most commonly reported hangover symptoms fall into eight main categories:
- General effects: fatigue, depression, distress and tremendous thirst
- Nociceptive symptoms: muscle pains or cramps, and headaches.
- Gastrointestinal disturbances: loss of appetite, stomach ache, nausea, vomiting and diarrhea.
- Increased activity in the sympathetic nervous system: increased systolic blood pressure, rapid heart rate (tachycardia), palpitations, tremors and perspiration.
- Sensory-perceptual symptoms: dizziness and hyper-sensitivity to sound and light.
- Sleep: general reduction in the amount of sleep and, paradoxically, an increase in slow-wave sleep.
- Cognitive symptoms: affects attention, concentration and short-term memory.
- Psychopathological symptoms: create a deficit in visual-spatial and psychomotor skills, and cause anxiety, depression and irritability.
The causes of hangover
Hangover may well be one of the least-documented alcohol-related subjects. Based on the research to date and an exhaustive review of the biological and medical literature on the subject, it is now possible to group the causes of alcohol hangover into two main categories: indirect and direct. Indirect causes are the dehydration, low blood sugar and sleep disturbance resulting from excessive drinking. The direct cause is the production of acetaldehyde.
1. Dehydration, low blood sugar and sleep disturbance
Excessive drinking assaults just about every part of the body, and organs under attack have to defend themselves. But the body’s physiological defense mechanisms lead to dehydration and low blood sugar. That shortage of water and sugar are what explain the particular discomfort of a hangover.
Obviously, the tremendous thirst associated with hangover is the result of dehydration. So are aching muscles and a throbbing head. When the body is dehydrated, it will draw water from any available source, including the brain. When it does this, the brain atrophies somewhat and the meninges (the protective covering around the brain) shrinks accordingly. The shrinking is what causes the headaches. Dehydration also means a serious loss of electrolytes, which can explain the cramps and muscle pains that generally accompany a hangover.
- Low blood sugar
A significant number of hangover symptoms are also those of hypoglycemia. This is no coincidence. Most of the alcohol a person drinks is processed by the liver, a remarkable organ that, among other things, produces glucose. But the liver can’t make glucose while it’s busy processing alcohol. Glucose is the primary source of energy for metabolism, and the substance most likely to affect the brain. A lack of glucose causes the brain to function abnormally, which is why, for several hours after drinking too much, a person will feel weak, tired, dizzy, anxious and depressed, and have difficulty concentrating and seeing clearly.
- Sleep disturbance
Studies have shown that one of the main reasons people feel so poorly the morning after getting drunk is the sleep disturbance caused by excessive drinking. Alcohol makes you sleepy, but it also alters the sleep cycle. Specifically, it can cause insomnia, make you wake up repeatedly during the night and exacerbate sleep disturbances. That’s why people can feel so tired and not in full control of their cognitive capacities the day after heavy drinking. Nobody sleeps well after tying one on.
2. Acetaldehyde production
As mentioned above, most of the alcohol a person drinks is processed by the liver. In so doing, the liver produces the enzyme alcohol dehydrogenase, which turns the alcohol into acetaldehyde, a very toxic substance. A high concentration of acetaldehyde has a variety of effects on the body, including reddening of the face, sweating, nausea, vomiting and tachycardia (accelerated heart rate). Given the similarity between these symptoms and those of alcohol hangover, some researchers hypothesize that the discomfort of hangover is a direct result of the metabolism of alcohol by the liver.