Drinking again

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understandinguncertainty.org was produced by the Winton programme for the public understanding of risk based in the Statistical Laboratory in the University of Cambridge. The aim was to help improve the way that uncertainty and risk are discussed in society, and show how probability and statistics can be both useful and entertaining.

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Alcohol can cause very serious problems, both for individuals, their families and society. But the Daily Mail’s story yesterday with the headline “Don't drink more than THREE glasses of wine a week: Oxford study claims slashing the official alcohol limit would save 4,500 lives a year” almost universally aroused derision among its many commenters. I was on World at One (31:27) discussing this Oxford study with one of the authors. I had to whip through the stats quickly so here is more of an explanation - I shall assume the science is correct and only deal with interpretation of their findings.

They modeled the effect of all drinkers reducing their consumption by 62%, so that the current median consumption of 13 gms a day drops to 5 gms a day, a median reduction of a unit (8 gms of alcohol) a day each. (I should add that this 62% reduction is not stated in their paper, but can be inferred from their use of log-normal distributions for fitting alcohol consumption).

They found around 4500 deaths were avoided or delayed each year from certain chronic diseases known to be associated with alcohol: these causes together lead to 170,000 deaths each year, so 4,500 is around 2.5%. These causes lead to around 36% of all deaths out of the England total of 550,000, so this 62% fall in alcohol consumption would be associated with around a 1% reduction in the total death rate each year. They did not model the effects on accidental or violent deaths, which would increase this figure, possibly even doubling it according to Australian guidelines. But frankly I’m surprised the effect is so little for such a huge change in behaviour.

Suppose we do assume that inclusion of accidents and violence doubles the benefits, so that everyone has their annual risk of death from chronic disease reduced by 2% each year. Then using current life-tables we can work out that, over a life-time, this adds up to around 11 weeks extension of life-expectancy . Assuming 60 years drinking, that’s around 5 minutes extra a day for a median reduction of one unit a day. Put this way, it doesn’t seem a huge benefit.

So while there probably is an increased risk from drinking above a low level, each extra unit only takes around 5 minutes off your life. This figure matches fairly well what we worked out when discussing the use of Microlives, and makes 6 units (around 2 pints of strong beer) roughly equivalent to 2 cigarettes or each day of being 5Kg overweight.

Of course if you are shoveling the stuff down, then 5 minutes a unit adds up, and possibly the loss per unit is higher for heavy drinkers. But at low levels people may well think it’s a reasonable trade-off.

But what about government guidelines? On World at One, the study’s author said that the duty of epidemiologists is to search and find out, and it is “up to other people to interpret that data”. But this does not seem to square with the categorical statement in the paper that

“On this basis, we recommend that the public health target for alcohol consumption in England should be to reduce median alcohol consumption to half a unit per day for both men and women.”

OK, this is a ‘public health target’ rather than government guidelines, but it is not surprising that this story was so badly reported when this kind of claim is made.

The crucial question that such a ‘public health target’ leads to is this: should government guidelines really be about trying to reach absolute rock-bottom risk? For example, the authors show that we could save even more lives by getting the 29% of teetotalers to do the decent thing and start boozing, but it is doubtful that this will become government policy.

And what would such “minimize-risk” advice do with children’s activities, sport, driving - in fact everything? I know this sounds like a Daily Mail diatribe against the nanny state, but even the HSE do not try to minimize risk, but base their judgments on the concept of ‘acceptable risk’.

Let’s hope that, when the new alcohol guidelines are established, they treat us all as intelligent adults rather than children and allow us to see the consequences of our actions in a clear way. This should be based on the type of evidence presented in this study, but perhaps interpreted rather differently.


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