Alcohol causes cancer. Well yes but….

A new study out of New Zealand says it does, though it’s worth looking at the detail

 

Alcohol, along with fat, salt and any number of other consumables, is a constant source of confusion when it comes to health.

It seems that as soon as scientists settle on the relative danger or safety of them, someone comes out the next day with a study that contradicts the previous assertions.

As I was growing up, salt became the target of public health advisories and warnings from the GP.

Salt causes heart problems and high blood pressure, they said. Stop using it.

More recently we’ve all been warned that low salt levels in our diets is causing sodium deficiencies, make sure you get enough salt.

And we’ve all read the articles saying that a glass of wine taken with a meal can actually help to prevent heart disease and strokes.

So when the headlines this last week in the newspapers and broadcast media announced that alcohol causes seven types of cancer it came as a bit of a shock to many people.

I think we can all be forgiven for wondering what had suddenly changed, but in truth, nothing has.

Alcohol has long been regarded as a contributory factor to some cancers, though the caveat has always been that its effect is dependent on the type and the amount of alcohol consumed as well as all the other lifestyle factors that have to be taken into account.

Make no bones about it, alcohol is a toxin; excessive drinking will have harmful effects, it doesn’t take a chemistry degree to know that.

Yet this latest pronouncement from the University of Otago in New Zealand seems to raise the bar to a whole new level.

“Alcohol causes seven different types of cancer” screamed the headlines.

Without drawing any particular conclusions or trying to undermine in any way the public health message of that announcement, it is worth examining the background and source of the information.

The findings are from a review of several other research studies, not from any original research specifically conducted for the purpose.

The sources data is taken from a decade’s worth of studies by the World Cancer Research Fund, the American Institute for Cancer Research and the International Agency for Research on Cancer, among others.

These are impeccable sources but the methodology is nonetheless clear, the review was looking for links between alcohol and cancer in the lifestyle and behaviour of cancer victims.

Nothing wrong with that, but it is very different from studying the effects of alcohol on a random sample of subjects.

It is the difference between discovering that, for example, of 50 cancer sufferers 45 of them drank alcohol regularly rather than finding that out of 200 regular drinkers 50 of them developed cancer.

There are other influences to take into account too.

The author of the study, Professor Jennie Connor, is an experienced and highly respected epidemiologist and public health expert, but her views on alcohol are strident and well known in her native New Zealand.

In her profile page on the Otago University website she says that New Zealanders are “in a state of denial about just how harmful our national drinking habits really are”.

She also chose to publish her article in the journal Addiction, so it is clear where her feelings on the subject lie, and that is not any disqualification, but it should be seen as advocacy.

In the study paper itself she explains her methodology which is that where she observed “evidence of an association of alcohol consumption with a disease, the inference that it is a causal association requires alternative explanations of the observed finding to be judged unlikely”.

That is to say, if the cancer patient drank and there is no other obvious explanation of what caused the cancer, she assumes the cause was alcohol.

On this basis she “suggests” there is “strong evidence” that alcohol causes cancer in the head, neck, oesophagus, liver, colon, rectum and breasts.

This allows her to extrapolate an estimate that “alcohol-attributable cancers at these sites make up 5.8% of all cancer deaths world-wide”.

At the same time Professor Connor declares that “Confirmation of specific biological mechanisms by which alcohol increases the incidence of each type of cancer is not required to infer that alcohol is a cause.”

So if we ignore the headlines for a moment and consider the evidence as presented it boils down to an assumption of causality in the absence of any other explanation without any idea as to how the causal mechanism actually works.

And that’s fair enough, but it is an assumption nonetheless.

So the headline should read “alcohol may cause seven types of cancer”.

Does that make matters any clearer…probably not.

Dlux spray

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