Red wine does not prevent breast cancerApparently, we can all relax. According to the Daily Telegraph, “A glass of red wine a day could help to prevent breast cancer, a new study shows [emphasis ours].”

There are two fairly substantial problems with this conclusion. The first and most important, is that alcohol actually increases breast cancer risk – and all types of alcohol at that. To put it bluntly, if everyone who read the headline went out and started drinking red wine regularly, more women would get breast cancer. More on this later.

The second issue, and the reason for the emphasis in the opening paragraph, is that the study didn’t show that a glass of red wine a day could help to prevent breast cancer. Here’s what the results actually showed:

The study

The researchers, from the Rogan lab at the University of Nebraska, were studying a chemical purified from red wine, called resveratrol. By looking at its effect on cancer cells in a laboratory, they found that resveratrol could prevent a type of DNA damage that has been implicated in breast cancer.

This damage involves oestrogen, a hormone which can increase the risk of breast cancer if people are exposed to raised levels over time. Our bodies can sometimes convert oestrogen into a form that can actually react with DNA, to create bulky extensions called “adducts”. There is some evidence that these adducts are a sign of the development of breast cancer, and can actually cause cancer in animals.

The researchers found that resveratrol blocks the process that creates these adducts. It turns on an enzyme called quinone reductase that switches the reactive version of oestrogen back into its inactive form. Even better, it only took low concentrations of resveratrol to do this.

So the paper provides preliminary evidence that purified resveratrol could help to reduce the risk of breast cancer. So where did the headline about red wine come from?

Three steps

We see reports like this all the time, and they almost always follow the same pattern:

  1. Chemical X affects cancer cells grown in a lab. It kills them or stops them from growing or changes the genes they switch on.
  2. Chemical X is also found in Food/Drink Y.
  3. Therefore, Food/Drink Y could prevent cancer.

Note that at the end of the first step, nothing untoward has happened. Reasonable experiments have been carried out, written up, peer-reviewed and published. Science is happy. Likewise, there’s nothing wrong about the second step either. We can measure the amounts of different chemicals in different foods.

It’s the third step that’s the problem. By the final full stop, we’ve leapt over so many logical hurdles in a single bound, that even Superman would stand on the sidelines looking awestruck. So what’s wrong with Step Three?

Three problems

For a start, in this case, it ignores the fact that red wine contains more than just resveratrol. On its own, resveratrol may indeed reduce the risk of DNA damage, but red wine is rife with hundreds of other compounds, many of which may not be so beneficial. Obviously, the most important chemical in red wine is the alcohol itself.

In your body, alcohol is converted into a chemical called acetaldehyde, which is not the sort of thing you want sloshing around your body. It’s one of the reasons for the nasty hangover the morning after, and because it can damage DNA, it is one of the most likely explanations for the cancer-causing effects of alcohol.

Step Three also ignores the fact that cells are not people. Laboratory experiments involving cancer cells are useful for providing clues about things that affect the risk of cancer. But as you can imagine, there’s a lot more going on inside your body than in a plastic dish, which is why the results of these experiments always need to be tested in large studies involving real people before we can draw any conclusions.

Fortunately, such studies exist. When it comes to alcohol and breast cancer, there are almost a hundred of them. In 2006, a group of researchers analysed the results of all of these and came to the following conclusions:

  • Every 10g of alcohol (about half a standard glass of wine) drunk per day increases the risk of breast cancer by 10 per cent.
  • Alcohol is responsible for 6 per cent of breast cancers in the UK, which works out to about 2,400 cases every year.
  • The results did not change when the researchers considered specific types of drink. All types of alcohol increased the risk of breast cancer.

If red wine – as opposed to, say, white wine or beer – does protect against cancer, we would expect to see that benefit reflected in the results of these large studies. It’s not.

Which means that, in concluding that red wine could prevent cancer, the final sin of Step Three is that it ignores the huge amount of existing evidence that arrives at the opposite conclusion.

The body of the Telegraph story takes these considerations into account – but the headline and opening sentence do not. And as such, someone reading this piece could very well go away with a public health message that’s founded upon three large logical fallacies and could increase the risk of cancer in people who follow it. That is not a simple misinterpretation of the facts – it’s a life-threatening one.

Resveratrol as an isolated chemical may one day be developed into a cancer-preventing drug. But red wine isn’t a magic bullet against cancer. If anything, it’s more ‘bullet’ than ‘magic’.