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.
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.
"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 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 spoken of with 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."
Below is a selection of your comments.
A further complication is working out how much, on average, one drinks each week. I regularly have weeks in which I do not drink, or have one pint. Equally, I might have weeks where I go to the pub or clubbing several nights and drink far more than is healthy. When asked, "How much do you drink on average each week?", what should someone in my position answer?
Tom Chester, Manchester, UK
I am pleased about the advent of unit specification on alcohol bottles, but am perennially surprised by the amount I drink. I like the occasional cider and tend to drink the bottled stuff rather than cans - Westons, Henneys etc - and some of them contain as much as 3.5 units per 500ml bottle. I have always considered myself to be a 'light' drinker, but just two of these bottles a week is half my recommended intake! Frightening, really. I probably would have guessed at two units because there's just shy of a pint in the bottles!
Calculating units from % alcohol and glass size isn't particularly complicated, unless the population is deemed incapable of maths usually learnt at the beginning of secondary school. One problem is that pubs/restaurants still don't usually provide info on drink strength or (often) measure size. Another issue is that - while foods are increasingly labelled in (frankly unnecessary) detail on nutrition - alcoholic drinks generally are yet to have their ingredients listed, let alone their nutritional content. As it happens, the thing that got me cutting down drinking was seeing a rare example where this info WAS provided, and realising a couple of bottles of beer provided 20% of my daily calories. Fat Britain and boozy Britain tackled in one!
Liz, London, UK
I know how much I drink: one unit every six months or so. I don't drink alcohol on a regular basis at all. I neither feel the need nor enjoy the taste enough to do that.
Tria Hall, Manchester, UK
Considering the guidelines for safe drinking were plucked out of thin air I'm not too worried. If I want to drink to excess on occasion and take a few risks here and there then I intend to, otherwise what is the point of being alive.
It's very easy for me to work out how much I drink. It's zero. But I feel increasingly that the rest of society thinks there must be something wrong with me for not wanting to play out every social interaction against a backdrop of excess alcohol consumption.
Steve Smedley, Woodbridge
I'm reading this article while at the Stockport Beer and Cider Festival mmm I think if my GP asks me next week about my recent consumption my memory will have to be 'selective', that's if I remember attending at all.....
Jeneve george, Manchester
A 12% bottle of wine is 9 units: anybody who buys wine knows how much a unit is. But people do not drink units. I drink way over the recommended amount, although I try to limit myself to half a bottle of wine a day, and I do not buy wine higher than 12% ABV, although sometimes buying a glass out it is a job to get anything that low, even with a dry white wine. However, since glass content is clearly marked on wine lists, I cannot believe that people don't know how much is in a glass. The trouble is, talk of units is irrelevant: it depends on the individual, how physically active one is, and so on.