Why Do Hangovers Happen?

Its the age old question and I get asked it constantly when I am working with young people in schools or delivering training; What’s a hangover? Why do I feel so horrendous the morning after (even when I’ve had a great night!)?

So I have had a look and decided that I would write today about the science of a hangover and can it be avoided?

Cause 1: Dehydration

Most people are aware of the fact alcohol is diuretic, which means it makes you wee more. The result is that the next morning you run the risk of dehydration along with a dry mouth and headache. Lovely stuff.

Prevention: Try to drink water between alcoholic drinks and/or drink water before you go to bed.

If you’ve ever tried the approach of downing a pint of water before you go to bed after a heavy night on le booze you’ll be aware of the fact that, although it may help, it doesn’t mean you get away hangover free. So there must be more to a hangover than just the dehydration…

In fact, it turns out alcohol is pretty poisonous and not just in the “what’s your poison?” sense, more in a surprisingly toxic way

Cause 2: Acetaldehyde

When we drink alcohol it is absorbed into our blood stream and works its way around our body. When it reaches the brain it makes you feel relaxed an uninhibited, which is the part we all enjoy, however this is not the only place alcohol leaves its mark. In the liver alcohol is metabolised (broken down) into different compounds which can then be removed from the body as waste. This process requires several steps before the final non-toxic products of water and carbon dioxide are made.

The first step is to turn the alcohol into acetaldehyde using an enzyme called alcohol dehydrogenase. The side effects of having acetaldehyde in your system include nausea, headaches and vomiting – sound familiar?

Prevention: There is none. I know – rubbish. You just have to wait for your body to metabolise the acetaldehyde into its less harmful by-products (roughly 1 unit of alcohol per hour). So unfortunately if you spend the morning having an unwanted date hugging the toilet you just have to wait it out. As acetaldehyde is even more toxic than alcohol moderation is probably the key.

Cause 3: NAD+ depletion

The metabolism of alcohol and acetaldehyde use a compound called NAD+. This NAD+ is also vital for the day to day health of your cells. It helps converts water, oxygen and a compound called pyruvate into energy. If the NAD+ has been used up metabolising alcohol, your cells need to make more. The cells convert pyruvate into lactate and this reaction produces more NAD+. Unfortunately long term build up of lactate is also linked to kidney damage. The more I read about alcohol the more I realise it’s pretty nasty stuff! The second consequence is that when pyruvate is converted to lactate, your liver becomes less efficient at regulating your blood sugar levels and blood sugar can become very low. Ever had the desire to eat the entire contents of your cupboards after drinking alcohol? That’ll be the low blood sugar.

Prevention: There’s not a lot you can do about the depleted NAD+ other than wait for your liver to do its magic (otherwise known as metabolism) and restore the natural balance. As for the low blood sugar, based on the assumption you’re not still hugging the loo, it’s a good idea to make sure you eat.

Cause 4: Reactive oxygen species and cell damage:

I’ve grouped these together because I don’t think it’s fair to say they cause a hangover however for regular drinkers they probably represent the biggest danger since they can cause longer lasting damage.

The acetaldehyde that is made during alcohol metabolism is a bit of a renegade and can attach itself to things in the cell that it shouldn’t, including a protein called glutathione. When attached to acetaldehyde, glutathione is prevented from doing other important jobs inside the cell which, when experienced regularly can lead to cell damage . More worryingly acetaldehyde can also bind to DNA and damage it, which can increase the risk of developing cancer (not a lot of people realise that drinking alcohol can lead to Cancer).

There is a separate chemical pathway that your liver cells can use to metabolise alcohol. Instead of using alcohol dehydrogenase it uses an enzyme called cytochrome p450. This method of alcohol breakdown still produces acetaldehyde but has the added bonus of churning out reactive oxygen species. These little nasties are, as the name suggests, incredibly reactive. They can cause a lot of damage to your cells by reacting with proteins and DNA. This method of breaking down alcohol is used far less by your cells than the alcohol dehydrogenase method so the less you drink the less likely you are to produce the reactive oxygen species.

Prevention: Eat food rich in cysteine post alcohol which includes eggs, chicken and oats. Cysteine is an important building block of glutathione, so making sure you get more into your body gives your cells a fighting chance at making more glutathione. Have a glass of vitamin C rich orange juice. Vitamin C is powerful anti-oxidant, meaning it can interact with the reactive oxygen species, preventing them from reacting with protein and DNA in your cells.

Obviously the best prevention for a hangover and damaging your health long term is avoiding alcohol in the first place. Regular exposure to alcohol and the damage caused to cells is linked to an increased chance of developing cancer. To me this is a far more important reason to avoid drinking than a fuzzy head the morning after and is a very good argument in favour of moderation. If you feel drunk that means there’s too much alcohol in your body for your liver to metabolise and you’re getting a backlog of alcohol related nasties in your system – so moderation really is key. Simples!


Bullock, C. (1990), The biochemistry of alcohol metabolism — A brief review. Biochemical Education, 18: 62–66. doi: 10.1016/0307-4412(90)90174-M. http://onlinelibrary.wiley.com/doi/10.1016/0307-4412(90)90174-M/pdf

Leave a Reply