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Steering clear of problems with alcohol at Christmas

Sipping sensibly and staying sober seems harder as Christmas and the new year approach. Though the days of Sister's sweet sherry, slurped on every ward, are long gone, there is still ample social scope for the staggering and slurring of cerebellar self-harm, the malaise of mucosal mayhem, and the horrors of hepatic hatchet-work. How to protect yourself and survive? This can be harder than it seems.

Suppose you decide to take the sensible precaution of sticking to safe drinking limits. You first have to find out what the safe limit is. The Government, having weighed the evidence, decided men could sensibly drink up to four units a day, and women up to three, without serious risk of harm. The RCGP still advises that sensible men will not drink more than 21 units a week, and sensible women 14, and the Office of National Statistics used those criteria in a survey of drinking patterns.

It discovered that 24 per cent of men and 14 per cent of women overstepped these limits. This is not encouraging, especially when the survey was conducted in the spring, and some people might still have been keeping their new year's resolutions.

The New Zealand government also advises 21 units as the limit for men, and 14 units for women; in the USA, recommended limits are 14 units for men, and seven for women.

The average limits probably don't apply to you anyway. I console myself with the thought that if you are an older man then you gain from drinking, because it reduces your risk of cardiovascular disease, and cardiovascular disease is common in older men. If you are a young woman, though, alcohol is more likely to do harm than good.

Confused by alcohol

Confused? This is not simply the booze going to your head. People cannot even agree on what constitutes a 'unit' of alcohol. The UK definition of a unit of alcohol is 10ml of pure ethanol ­ that is, near enough 8g of pure ethanol.

In Australia and New Zealand, 10g of ethanol is taken to be one unit; and the hard-hitting American unit weighs in at 12g. This means the Australians and New Zealanders are the most lenient when it comes to drinking: antipodean women are advised that it is safe to drink 40 per cent more than their American cousins.

You may feel in need of a stiff drink just reading how hard it is to decide on the number of units that are safe for you. But worse is to come. Faced with a real pint of real ale, or a glass of fine burgundy, how do you tell how many units it might contain? If we base our unit on the 10ml (8g) value, which makes calculation fairly easy, all we need to know is the volume of drink and the percentage ethanol by volume. But these are not easy to guess.

The strengths of beers range from about 3.4 per cent to 9 per cent v/v; white wine from 8 per cent to 13 per cent v/v; and spirits from 37.5 per cent by volume for mass market vodka to over 57 per cent by volume for cask-strength '10-year-old Laphroaig' or 'Wood's Old Navy Rum 100'. One merchant advertises a Speyside malt called 'Tormore, Raw Cask, Blackadder, Cask Strength 1990' which is alleged to contain 65 per cent ethanol by volume.

The different volumes of 'standard' measures are just as befuddling as the different strengths. In the UK, a single pub measure of spirits is now 25ml. Once upon a time it was 1/6 gill (1/24 pint) in England and 1/4 gill (1/16 pint) in Scotland. A half pint of beer is 284ml. Bottles and cans hold anything from 250 to 500ml.

A glass of wine in a pub can contain 175ml, but other measures are also permitted, and fortified wines usually come in 50ml 'double' measures. So it is handy to have your calculator with you to work out that a pint (568ml) of 'Brakspear Special' (4.3 per cent by volume) contains 24.42ml of pure ethanol, or 2.442 British units. There is a great deal to be said for the campaign to enforce labelling of drinks with the number of units.

Drinking and driving

Drinking moderate amounts of alcohol may be safe at home, but can be very dangerous as soon as you sit behind the wheel of a car. The legal limit in the UK is a generous 80mg per 100ml of blood. Driving performance is already impaired at concentrations of 30mg per 100ml, and there is dismay in road safety circles that a lower limit of 50mg per 100ml will not now be introduced. As far as I know, no one has looked at the influence of ethanol on diagnostic skills or surgical prowess.

The amount of ethanol you need to take you over the legal limit is also hard to predict. It depends on several factors, notably sex and body size. Both these factors influence the volume of water in the body ­ women have proportionately more fat and less water ­ and total body water is a major determinant of the maximum blood ethanol concentration after drinking a specified amount.

The peak concentration also depends on the rate of absorption. There is not much evidence that 'lining your stomach' with olive oil will help, but experiments with minced-up meat-and-two-veg show how the time to peak and the height of the peak concentration can be blunted by food. The explanation seems to be that food inhibits stomach emptying, and so delays transit of ethanol from the stomach to the duodenum. Hardly any ethanol is absorbed from the stomach, and almost all is absorbed in the small intestine, so the longer it takes to get there, the slower absorption; and the slower absorption, the blunter the peak.

So what does it mean for the risk-taking driver? A man who weighs 70kg and is 180cm tall might have to drink about five units (40g of ethanol) to exceed the limit, but four units would see a woman of 60kg and 170cm over the 80mg per 100ml. Since there is a fair amount of inter and intra-individual variation, no sensible driver would risk losing his or her licence by drinking more than about three units, and the prudent would avoid alcohol altogether.

And another thing. Trials of drugs such as propranolol and clomethiazole show little or no evidence of benefit in patients with a hangover. Merry Christmas!

Confusion is not simply the drink going to your

head ­ people can't even agree on what constitutes

a 'unit' of alcohol~

With the evidence-base on sensible drinking unclear and 'safe' limits so confusing, Dr Robin Ferner fears for the tipplers as Christmas and the new year approach

Calculating alcohol

Number of ml pure ethanol =

number of ml drink x (per cent ethanol by volume/100)

And one UK unit = 10ml pure ethanol

So 500ml of beer, 4 per cent v/v, contains 500 x 4/100

= 20ml pure ethanol

= 2 UK units ethanol

(And 20ml pure ethanol = 16 grams pure ethanol)

Alcohol by volume and calculated units*

for a variety of drinks

Boddingtons (568ml) 3.8 per cent 2.16 units

Bass (568ml) 4.4 per cent 2.50 units

Stella Artois (568ml) 5.2 per cent 2.95 units

Leffe (330ml) 6.5 per cent 2.15 units

Diamond White (275ml) 7.5 per cent 2.06 units

Hoegaarden Forbidden Fruit (330ml) 9.0 per cent 2.97 units

Trappiste Rocheforte 10 (330ml) 11.3 per cent 3.73 units

*calculations based on information provided and rounded to two decimal points

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