Skeptics Stack Exchange is a question and answer site for scientific skepticism. It only takes a minute to sign up.
Sign up to join this community
From an NHS website:
To lower your risk of health problems, the NHS recommends that:
men should not regularly drink more than 3-4 units of alcohol a day
women should not regularly drink more than 2-3 units of alcohol a day
'Regularly' means drinking these amounts every day or on most days of the week.
Do these figures have any scientific basis?
They made it up. Moreover, a single limit for all doesn't make sense given what we know about alcohol metabolism.
Richard Smith, a former editor of the BMJ, was on the panel that set the UK advisory limits for alcohol consumption in 1987 and he was reported to have said the limits were made up. One currently accessible (I think the original was in the Times, currently paywalled) report tells the story like this:
Richard Smith, a member of the Royal College of Physicians working party that produced the recommendations, told the paper the limits were prompted by "a feeling that you had to say something". He said: "Those limits were really plucked out of the air. They were not based on any firm evidence at all. It was a sort of intelligent guess by a committee." The committee's epidemiologist had confessed that "it's impossible to say what's safe and what isn't" because "we don't really have any data whatsoever", Mr Smith said. The former editor of the British Medical Journal said members of the working party felt obliged to produce the guidelines because of concerns over growing evidence of the chronic damage caused by heavy, long-term drinking
Read more: http://www.metro.co.uk/news/71872-government-guessed-alcohol-limits#ixzz1nbWGAoMV
Moreover, there are good reasons to doubt the wisdom of any simplistic, population-wide advice. Anecdotally the human response to alcohol varies widely. Some people get ill, some get violent, some get mellow, some seem to drink with impunity from harm. And, at least for many western populations, we know that some alcohol is good for you so recommending abstinence isn't good advice.
The human ability to metabolise alcohol depends on alcohol and aldehyde dehydrogenase enzymes which vary a lot across populations (one theory being that agriculture and the ability to make alcohol, alongside large cities where the water supply is bacteriologically suspect generates selective pressure to cope with alcohol as booze+dirty water = clean water) and within populations. Some academic reviews of this heterogeneity are here and here.
Richard Smith sums it all up in a recent BMJ blog reporting a debate on the topic he had recently participated in:
I agreed that it’s difficult to set safe limits. I remember the debate at the working party nearly 30 years ago when the epidemiologist said it was impossible to set limits because the evidence was poor. Then there are the problems that the possible consequences of alcohol are hugely varied, including both social and medical problems, people are all different in size, body composition, and responses to alcohol, and the amount of alcohol even within the same category of drinks (beer, wine, or spirits) varies considerably.
The best advice might be to find your personal tolerance and not consume beyond it, but governments sometimes don't like to trust individuals with responsibility like that.
One of the interesting aspects of the recommendations for Alcohol limits is the contrast between different countries.
Wikipedia* shows a list of different recommendations, and the different is stark: 24g per day in the Czech Republic, and 40g per day in Italy.
While this doesn't mean that there is no scientific basis, it does suggest that the interpretation of that evidence varies so widely as to render it fairly insignificant.
Personally I think that the limits are set more for Political reasons (being seen to be pro-health or anti binge-drinking).
*I wouldn't normally quote Wikipedia as a source, but this is fairly impirical so I feel more safe in doing so than usual.
Yes and No
Acording to this article there is sound science underlying the original weekly alcohol consumption recommendations.
"The weekly limits were based on robust studies and were set at a level at which alcohol harms outweigh any putative benefit."
However unfortunately the popular interpretation of the weekly limits was that people could drink the entire weekly allowance in one night, and this was leading to the 'binge drinking' phenomenon, which is definitely not good for you and leads other problems related to drunkenness. The daily limits were introduced in order to counteract this.
However again unfortunately this has led to people believing that they could drink every day with no ill-effects (the original recommendations included having two or three alcohol-free days per week). Again there can be problems with drinking every day, even in moderation.
In short: the original weekly recommendations were based on science. The recommendations were modified to a daily amount fix a specific problem. Since the daily limits were based on the old weekly limits there is still something of a scientific basis, but it is less certain.
EDIT:There are good arguments that the guidelines are very much simplified from what an accurate 'safe' limit would be for each person. I also have sympathy with the people who claim there is not such thing as a 'safe limit' (just as there is no such thing as a 'safe speed' at which to drive). However there was certainly a science component to the guidelines, even if politics and communicability also played a part in their formulation.
