Feeling Green: The Science Behind a Hangover

With Saint Patrick’s Day just around the corner, many of us are pulling out our green socks and “Kiss me, I’m Irish” shirts in anticipation of a day of celebration. The day after all the pinching and partying, however, some of us may wake up with a pounding headache, nausea, sensitivity to light and sound, and the general sense that we have joined the ranks of the living dead. I speak, of course, of the hangover. But what causes these unpleasant side effects? Why are some people more affected than others? And what can you do to get rid of one?

If you think back to the AlcoholEdu program we all took as a part of orientation you may remember being told that hangovers are caused by the dehydrating effects of alcohol. This is an oversimplification. In reality, there is no scientific consensus on what actually causes a hangover, but I will explore some of the most prominent explanations.

The first is actually dehydration. Ethanol inhibits the release of vasopressin, a hormone that causes the kidneys to retain water in the blood. This decrease in vasopressin leads to the familiar increased urination, which may cause dehydration if the water is not replenished. This would suggest that drinking water with your alcohol would eliminate any morning-after trouble, but alas, this is not always the case.

Another common explanation is that it's not the ethanol itself that causes hangover symptoms but rather the compound that alcohol is converted into when it’s digested. As soon as alcohol enters the blood, an enzyme in the liver called alcohol dehydrogenase (ADH) goes to work converting ethanol into acetaldehyde. Acetaldehyde is toxic and if you drink too much, it can build up in the bloodstream and lead to some of the unpleasant side effects associated with alcohol consumption.

Fortunately, there exists another enzyme named—you guessed it—aldehyde dehydrogenase (ALDH) that converts harmful acetaldehyde into harmless acetate. Normally, small quantities of ethanol can be quickly metabolized into acetate, but as the number of tally marks on your arm goes up, ADH and ALDH can become saturated, meaning they cannot keep up with the rate at which alcohol is entering the system.

Thus, binge drinking can cause elevated levels of toxic metabolites which contribute to hangover symptoms. Interestingly, the amount of ALDH varies among individuals and depends on genetics. This may help explain why some people have never had a hangover, while others wake up in pain after just a couple drinks.

Acetaldehyde is not the whole story, though—there are other compounds found in alcoholic beverages besides ethanol. The chemical impurities found in booze are called congeners, and they are the byproducts of the fermentation process that created the ethanol in the first place. The most notorious congener is ethanol’s evil little sibling, methanol. Methanol is extremely toxic and it's the compound responsible for the blindness and death caused by drinking bad moonshine. Inexperienced moonshiners may inadvertently collect methanol alongside ethanol during distillation and serve up toxic hooch instead of Appalachia’s finest. But I digress.

Even quality alcohol such as brandy or whiskey can contain small quantities of methanol. When methanol enters the blood, it, too, is metabolized by alcohol dehydrogenase, but instead of forming acetaldehyde, methanol is converted into formaldehyde. Yes, that is the same formaldehyde used to preserve dead animals for dissection. Needless to say, formaldehyde is bad news for living things. It turns out that distilled spirits with the highest concentrations of methanol are the most likely to cause hangovers, and drinks like vodka are the least likely to cause them.

The presence of congeners like methanol may explain the efficacy of the 'hair of the dog' remedy for hangovers. Alcohol dehydrogenase has a higher affinity for ethanol than for methanol, so a hair of the dog that bit you the next day (read: “Another Sip of Booze”) may actually block the conversion of methanol into formaldehyde, temporarily relieving hangover symptoms. At some point, though, all of the ethanol will be metabolized, ADH will go back to work on methanol, and the hangover will return. And if you drink something with more methanol, you will not just prolong your suffering but actually make it worse.

You can purchase aldehyde dehydrogenase pills that allegedly relieve the symptoms of over-imbibing, but the enzyme is almost certainly destroyed in the harsh acidic environment of the stomach before it makes it into the bloodstream. For now, it seems all we can do is stay hydrated and choose drinks with low quantities of congeners. So this Saint Patrick’s Day, maybe you’ll pass on the beer and Irish whiskey and opt for vodka and cranberry juice, or maybe you’re inclined to try the latest corned beef and cabbage juice remedy. To those who choose the former, science is on your side. Happy Saint Patrick’s Day.

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