Biology of a Hangover: Vasopressin Inhibition
When alcohol is consumed, it enters the bloodstream and causes the pituitary gland in the brain to block the creation of vasopressin (also known as the antidiuretic hormone). Without this chemical, the kidneys send water directly to the bladder instead of reabsorbing it into the body. This is why drinkers have to make frequent trips to the bathroom after urinating for the first time after drinking.
According to studies, drinking about 250 milliliters of an alcoholic beverage causes the body to expel 800 to 1,000 milliliters of water; that's four times as much liquid lost as gained. This diuretic effect decreases as the alcohol in the bloodstream decreases, but the aftereffects help create a hangover.
The morning after heavy drinking, the body sends a desperate message to replenish its water supply -- usually manifested in the form of an extremely dry mouth. Headaches result from dehydration because the body's organs try to make up for their own water loss by stealing water from the brain, causing the brain to decrease in size and pull on the membranes that connect the brain to the skull, resulting in pain. [ew]
The frequent urination also expels salts and potassium that are necessary for proper nerve and muscle function; when sodium and potassium levels get too low, headaches, fatigue and nausea can result. Alcohol also breaks down the body's store of glycogen in the liver, turning the chemical into glucose and sending it out of the body in the urine. Lack of this key energy source is partly responsible for the weakness, fatigue and lack of coordination the next morning. In addition, the diuretic effect expels vital electrolytes such as potassium and magnesium, which are necessary for proper cell function.
Different types of alcohol can cause different types of hangover. In the next section, we'll look at the differences.
Biology of a Hangover: Congeners
Different types of alcohol can result in different hangover symptoms. This is because some types of alcoholic drinks have a higher concentration of congeners, byproducts of fermentation in some alcohol.
The greatest amounts of these toxins are found in red wine and dark liquors such as bourbon, brandy, whiskey and tequila. White wine and clear liquors such as rum, vodka and gin have fewer congeners and therefore cause less frequent and less severe hangovers. In one study, 33 percent of those who drank an amount of bourbon relative to their body weight reported severe hangover, compared to 3 percent of those who drank the same amount of vodka.
Because different alcoholic drinks (beer, wine, liquor) have different congeners, combining the various impurities can result in particularly severe hangover symptoms. Additionally, the carbonation in beer actually speeds up the absorption of alcohol. As a result, following beer with liquor gives the body even less time than usual to process the toxins.
Biology of a Hangover: Acetaldehyde
A product of alcohol metabolism that is more toxic than alcohol itself, acetaldehyde is created when the alcohol in the liver is broken down by an enzyme called alcohol dehydrogenase. The acetaldehyde is then attacked by another enzyme, acetaldehyde dehydrogenase, and another substance called glutathione, which contains high quantities of cysteine (a substance that is attracted to acetaldehyde). Together, the acetaldehyde dehydrogenase and the glutathione form the nontoxic acetate (a substance similar to vinegar). This process works well, leaving the acetaldehyde only a short amount of time to do its damage if only a few drinks are consumed.
Unfortunately, the liver's stores of glutathione quickly run out when larger amounts of alcohol enter the system. This causes the acetaldehyde to build up in the body as the liver creates more glutathione, leaving the toxin in the body for long periods of time. In studies that blocked the enzyme that breaks down acetaldehyde (acetaldehyde dehydrogenase) with a drug called Antabuse, designed to fight alcoholism, acetaldehyde toxicity resulted in headaches and vomiting so bad that even alcoholics were wary of their next drink. Although body weight is a factor (see How Alcohol Works), part of the reason women should not keep up with men drink-for-drink is because women have less acetaldehyde dehydrogenase and glutathione, making their hangovers worse because it takes longer for the body to break down the alcohol.
Some of the most common hangover symptoms -- fatigue, stomach irritation and a general sense of illness all over -- can be further attributed to something called glutamine rebound. In the next section, we'll see what this aftereffect is all about.
Biology of a Hangover: Glutamine Rebound
After a night of alcohol consumption, a drinker won't sleep as soundly as normal because the body is rebounding from alcohol's depressive effect on the system. When someone is drinking, alcohol inhibits glutamine, one of the body's natural stimulants. When the drinker stops drinking, the body tries to make up for lost time by producing more glutamine than it needs.
The increase in glutamine levels stimulates the brain while the drinker is trying to sleep, keeping them from reaching the deepest, most healing levels of slumber. This is a large contributor to the fatigue felt with a hangover. Severe glutamine rebound during a hangover also may be responsible for tremors, anxiety, restlessness and increased blood pressure.
Because alcohol is absorbed directly through the stomach, the cells that line the organ become irritated. Alcohol also promotes secretion of hydrochloric acid in the stomach, eventually causing the nerves to send a message to the brain that the stomach's contents are hurting the body and must be expelled through vomiting. This mechanism can actually lessen hangover symptoms in the long run because vomiting gets rid of the alcohol in the stomach and reduces the number of toxins the body has to deal with. The stomach's irritation may also be a factor in some of the other unpleasant symptoms of a hangover, such as diarrhea and lack of appetite.
So now we know why alcohol causes hangovers. In the following sections, we'll look at the science behind the most common hangover "cures."
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