Doctors should ask patients about their drinking habits as a matter of routine, say health advisers. But do you really know the answer?
It was so much easier in the old days.
A small glass of wine. Half a pint of lager. Or a small whisky.
They all contained roughly one unit of alcohol, which is 10ml of pure alcohol. At least, that was the general rule of thumb, however erroneous it was.
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But then wine glasses enlarged, lager became more potent and spirit measures more varied, and the system for counting became more complex.
Some doctors already broach the subject of alcohol intake with their patients. But this week the National Institute for Health and Clinical Excellence (Nice), which advises the government, recommended that patients should be asked more often.
Doctors shouldn't expect an accurate answer, says Don Shenker, chief executive of Alcohol Concern, because people don't want to face up to how much they drink. And even if they want to be honest, it's not easy for them to say how many units of alcohol they consume.
"Although 90% of people have heard of units as a concept, only about 13% can calculate them, so we are still very unit illiterate," he says.
Labelling of unit content on alcohol sold in supermarkets, off-licences and pubs must improve and should be mandatory, he says.
"I have no idea about units, although I should do. In the past I thought about it when there was a government campaign, but that's disappeared now and I don't count units at all. Even if I wanted to, it would be hard to know, because when you order a glass of wine, the glasses are often different sizes"
"When you go into a bar or pub and order a glass of wine, you have no idea how many units are in it, unless you really know your stuff. It's two or three, depending on the size.
"If it's a 14% bottle of wine, then a 175ml glass of white wine will be 2.3 units but if it's a small glass, it will be 1.8 units and if it's an 11% [alcohol by volume] bottle, it's less than that."
So it's complicated, he says, and there needs to be a concerted government effort to educate drinkers, supermarkets and pubs about what each drink contains. To make it simpler, we should be less precious about decimal points and just round up or down, he says, so a glass of wine is about two units and a pint of lager about three.
The proposal that doctors should raise this question more regularly has led to accusations from some quarters that it is another example of the state prying and nannying, but Mr Shenker says such action can save lives and also ease the burden on the NHS.
"Many people are not aware that their drinking carries a health risk, and it's only when GPs ask about it and link it to a medical condition, that they cut down.
"Of course, they might still ignore the GP's advice but evidence suggests that one in eight heavy drinkers reduce their drinking when the issue is raised by their GP, compared with only one in 20 smokers. This would save the NHS a lot of money."
Another reason why people underestimate their intake is that they tend to pour large measures when drinking at home, says Chris Sorek, chief executive of Drinkaware, which promotes responsible drinking.
"People pour on average nearly double what they should, meaning they may be unintentionally exceeding the daily unit guidelines and inadvertently putting themselves at risk of the physical, social and mental harms associated with drinking to excess."
All these individual discrepancies - between what people think they drink and what they actually drink - make up a huge national deficit, according to the Centre for Public Health at Liverpool John Moores University.
Researchers estimated that the difference between consumption figures supplied by the General Household Survey, which is one of the government sources, and figures from alcohol sales is 430 million units a week, or a bottle of wine per adult drinker per week.
"The level of knowledge is much better but I'm not convinced it's had a big impact on people's behaviour. People are still fairly bad at it. One of the main areas is estimating portion sizes, so even though they may have a good feel for which foods are energy-rich or energy-poor, they're not able to translate that into how much of those foods is appropriate to eat"
Professor Simon Langley-Evans, head of nutritional sciences at the University of Nottingham
The latest NHS figures were published two weeks ago and they suggest that in England, the average weekly consumption in 2008 was nearly 17 units for men and nearly nine units for women.
But the research in Liverpool, which also allows for 14% of the population being teetotal, says for those adults that drink, the average is 26 units a week, combining men and women.
Mark Bellis, who led the research in Liverpool, says people just don't tell the truth in surveys, partly because they genuinely don't remember but also because they are selective.
"People immediately exclude periods of heavy drinking, like a wedding or a birthday, because they don't think it's typical. This may be one day a week or one day a fortnight they may exclude.
"And we're coming up to a month now, the World Cup, that people will probably leave out altogether."
But there is a wider and more complex issue to address than counting units, says former GP Ian Banks, now a doctor in accident and emergency in Belfast.
He says questioning patients like this is a "nonsense", because drinking binds many UK communities and is viewed in terms of pride.
"They would just say 'Hey, I drank 50 units last night.' Instead of pontificating and preaching to people, you have to know more about why they drink so you can do something about it, rather than legislating against it."
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