Why don't some people get hangovers?

Kat Arney put this question to Chris Smith...

Chris - Well I did a little bit of practical experimentation myself over Christmas and I must admit, I did have one or two.

Kat - I've got a terrible one today.

Chris - And Kat is confessing that she is currently suffering.

John - You see I've got two sisters. Myself and one sister never, ever get hangovers and my other sister does.

Chris - I suppose in answering this question John, one has to consider - well what is a hangover? A hangover is a combination of dehydration because alcohol is a diuretic and it encourages you body to lose water, and this means that the salt balance of your body goes off kilter, which contributes to you feeling not very well. The other thing that alcohol is, it's ethyl alcohol, and this is a metabolic precursor for acetaldehyde, which is about one carbon atom and a few hydrogen atoms different from the same stuff we use to embalm bodies in a mortuary - that's formaldehyde. And when you break down alcohol, one of the intermediates in the breakdown process is acetaldehyde and that then goes round your body fixing your tissues and also contributes to some of the nasty symptoms. Now, why is it that some people get these symptoms and others don't? Well there was a big study done in Australia, actually. They looked at 4,000 people on the twin registry. They found about 40-45% of the hangover effect is down to genes, the other half probably down to behaviour, and body size, and so on. In other words - what will genes be doing? Well, they'll be affecting your ability to handle the levels of acetaldehyde; they'll be affecting those levels of those enzymes in your body that break down alcohol and, therefore, eliminate those toxic intermediates from you body. And, therefore, how your metabolism handles alcohol is going to be at least half of the situation. So, if you are prone to hangovers, you're probably not going to improve through training very much. A little bit of training can improve things by increasing the levels of the enzymes your liver makes, but not very much so, it's probably better as they say to steer clear. Kat - So basically I've pickled myself today?

Chris - Yes basically - sorry.