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Tuesday, 1 February, 2000, 04:56 GMT
Why people topple after a tipple

drink Drinking to excess can cause blackouts

Passing out after a few too many drinks is a common problem for heavy drinkers - and scientists now think they know why it happens.

The discovery will not give the green light to indulge, but it may help explain the causes behind one of the potential downsides of a night out.

Until now, the reason why people topple over after hitting the bottle has remained a mystery.

We're all aware of people who, after drinking considerably, get up to leave, stagger and then pass out. But exactly why they pass out after drinking alcohol has never been fully understood
Dr Virend Somers
Researchers at the University of Iowa College of Medicine and the Mayo Clinic in Minnesota say the effect of alcohol on blood vessels is to blame.

They found, in a study of healthy young adults, that blood vessels do not tighten so effectively after drinking, causing low blood pressure which can be responsible for fainting.

"We're all aware of people who, after drinking considerably, get up to leave, stagger and then pass out," said Dr Virend Somers, at the Mayo Clinic. "But exactly why they pass out after drinking alcohol has never been fully understood."

Low blood pressure

Krzysztof Narkiewicz, lead author of the study published in Circulation: Journal of the American Heart Association and an associate professor at the Medical University of Gdansk, Poland, said it was the first time a link had been made between alcohol, low blood pressure and impaired constriction of blood vessels.

Some people, including those with diabetes, the elderly and people on medicines that dilate blood vessels, experience light-headedness when they stand up because of low blood pressure.

Dr Somers added: "Drinking alcohol might magnify their risk of fainting and injury from falling. Alcohol appears to disrupt this mechanism even in healthy young people, at fairly modest levels of alcohol intake."

The research was carried out on 13 men and one woman, with an average age of 26, who reclined in a metal cylinder while a vacuum was applied to it to lower the pressure on their bodies. This simulated the gravitational stress of standing up.

The message should be - don't get so drunk that you pass out
Professor Griffith Edwards, National Addiction Centre
Blood flow in their forearms was measured at four different gravitational levels after having a non-alcoholic drink to determine how much their blood vessels tightened in response to a drop in blood pressure.

The tests were then repeated on another day after the subjects had drunk two to three beers.

During the alcohol-free tests, vessels constricted normally and blood pressure did not significantly change, except with extreme negative pressure. After drinking alcohol, blood pressure dropped substantially.

Professor Griffith Edwards, professor of addiction behaviour at the National Addiction Centre in London, said: "Everyone knows that people sometimes tip off bar stools, but no-one has done much research on why. This sounds quite interesting because they are saying people have hypotension and they pass out for that reason.

"The message should be - don't get so drunk that you pass out."

But he added: "I doubt this is the only explanation. There are other explanations such as lower blood sugar levels and motor co-ordination, which is paralysed by alcohol."

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