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Patrick Basham and John Luik on alcohol and cancer

03-Mar-2009

Tuesday 3 March 2009
Women, keep drinking
Why was a flimsy study apparently showing a link between booze and breast cancer so uncritically accepted?
Basham and Luik

 

For over a decade, a constant stream of studies has warned women who drink that they run an increased risk of getting certain cancers, particularly breast cancer. But this steady stream of anti-drinks advice last week gave way to a global torrent when two new studies about the link between drinking and cancer in women received huge, and typically uncritical, international media attention.

The study that attracted the most attention is sponsored by Cancer Research UK and was published in the Journal of the National Cancer Institute. The lead researcher, Naomi Allen from Oxford University, told the Guardian: ‘Given that this is the largest study in the world to look at this, it’s clear that even at low levels of alcohol consumption, there does seem to be a very significant increase in cancer risk, and most women are probably not aware of that.’

Allen came across with even scarier news for Americans, telling the Washington Post that the ‘take-home message’ was this: ‘If you are regularly drinking even one drink per day, that’s increasing your risk for cancer [since] there doesn’t seem to be a threshold at which alcohol consumption is safe.’

One can’t help but wonder just what Allen herself has been drinking in the Senior Common Room at Oxford. After all, her public pronouncements, her recommendations to government, and the reports about her study in the media are certainly not supported by her results.

First, Allen’s study is an observational one, based on data from the UK’s Million Women Study, which is a study about the association between Hormone Replacement Therapy and cancer and heart disease. Allen’s study comes from self-reports about the drinking habits of women in that study.

This means that the study, as an observational study – the weakest kind of epidemiological endeavour and certainly nothing close to the gold standard of a randomised controlled trial – is inherently unable to draw any causal conclusions about a link between drinking and cancer.

Second, the study fails to meet even the most basic requirement of science – that is, being able to validate its measurements – since it is entirely based on the women’s self-reports of their recollection of their drinking. None of these reports was checked and the authors can make no claim about how reliable they are. No one knows how much or how little these women really drank since no one bothered to measure it.

This makes any conclusions based on such ‘evidence’ just a tad dicey. At its foundation, therefore, the study can’t warrant that any of its data about the key fact – the drinking habits of its subjects – is accurate.

However, the worst is yet to come.

Third, the study is full of significant puzzles that suggest that its results are unreliable. For example, it reports that the incidence of all types of cancer studied in its non-drinking subjects was 5.7 per cent compared with 5.3 per cent for those subjects who had at least a drink a day, and up to 14 drinks a week.

In other words, not only was there no dose-response in terms of cancer risk, but teetotallers had a higher population incidence of cancer than those consuming up to 14 drinks a week!

Even those women in the study who drank the most (15 or more drinks a week) had a cancer incidence of 5.8 per cent, which is virtually identical to those who drank nothing. But this particular take-home message somehow escaped Allen’s notice, and that of the media as well.

Fourth, the study looked at 21 types of cancer incidence. Of these, it found statistically significant associations between drinking and only four types of cancer. Moreover, these associations were barely significant.

The association with breast cancer, with by far the largest number of cases in the study (almost 22,000), was non-significant. Therefore, of the cancer-drinking correlations examined, virtually none was statistically significant.

What is the real take-home message of this study? Perhaps it should be to avoid drinking policy advice produced by Oxford epidemiologists.

Patrick Basham and John Luik are authors, with Gio Gori, of Diet Nation: Exposing the Obesity Crusade, a Social Affairs Unit book. (Buy this book from Amazon(UK).) Patrick Basham directs the Democracy Institute and is a Cato Institute adjunct scholar. John Luik is a Democracy Institute senior fellow.


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