The link between cancer and smoking is undeniable. If you smoke, the most important thing you can do to reduce your risk of cancer is to stop. And decades of research and policy action have made this fact clear.

But what about other risk factors for cancer? Could the well-known dangers of smoking be used to nudge people to think about alcohol as a health risk?

Research making headlines today has made attempts to find out, by asking: ‘How many cigarettes are in a bottle of wine?’

Based on statistical analysis the researchers say that drinking a bottle of wine a week carries the same lifetime cancer risk as smoking up to 10 cigarettes a week in women and 5 in men.

And the researchers, publishing their study in BMC Public Health,say this “provides a useful measure for communicating possible cancer risks that exploits successful historical messaging on smoking”.

How many cigarettes are in a bottle of wine?

The study was based on the risk of someone developing any form of cancer in their lifetime. The authors calculated that in people who don’t smoke, the extra risk of developing cancer at some point in their life caused by drinking10 units of alcohol per week was 1.0% for men and 1.4% for women.

UK alcohol guidelines say men and women shouldn’t drink more than 14 units a week on a regular basis. And 10 units of alcohol is equivalent to one 750ml bottle of wine.

This means that if 1,000 men and 1,000 women each drank one bottle of wine per week, around 10 extra men and 14 extra women may develop cancer during their lifetime.

They then calculated that the ‘cigarette equivalent’ of a bottle of wine per week – the number of cigarettes needed to have the same impact on lifetime risk as a bottle of wine. They concluded this would be 5 cigarettes for men and 10 for women.

This is an interesting way to make people think about the health effects of moderate drinking, but unpicking these figures brings a few things to light.

Putting alcohol and smoking head to head

First, this calculation includes the impact of alcohol and smoking on all types of cancer combined. Even though a few cancer types are linked to both smoking and alcohol, some are more strongly associated with one risk factor than the other.

Drinking alcohol increases the risk of mouth, upper throat (pharyngeal), oesophageal, voice box (laryngeal), breast, bowel and liver cancer. Whereas smoking is linked to at least 15 types of cancer, the most common being lung cancer.

Dr Katrina Brown, Cancer Research UK’s statistical information and risk manager, says focusing on the result for all cancers combined might downplay the impact each risk factor has for individual cancer types.

“There are certainly downsides to comparing risk factors in this way,” says Brown.

These figures should be viewed more as illustrative rather than precise.

– Dr Katrina Brown, Cancer Research UK

“Take lung cancer for example. For lung cancer, drinking a bottle of wine would not have the same effect as smoking 10 cigarettes, because smoking has a much bigger impact on lung cancer risk than drinking alcohol does.”

But the picture is different when talking about breast cancer. Of the cancers linked to alcohol, drinking causes more cases of breast cancer than any other type in the UK – because breast cancer is the most common of the alcohol-related cancer types. Stats from 2015 suggest that around 8 in 100 breast cancer cases were linked to alcohol. That’s why the researchers saw a bigger overall impact in women from that weekly bottle of wine, because the biggest cancer type linked with alcohol is by far more common in women than men.

So, communicating the risk of drinking alcohol, and the comparison between smoking and drinking, in a way that groups all cancers together might not be the most informative option.

“It’s particularly important to consider that some individuals might have a higher risk for specific cancers because of other risk factors like obesity, or genetics,” says Brown.

“It’s also possible that people are less accurate at estimating their intake of alcohol than of cigarettes, or vice-versa. That would impact the accuracy of the calculations which give those precise figures of 10 cigarettes versus 1 bottle of wine. So these figures should be viewed more as illustrative rather than precise.”

Let’s get some perspective

We also need to think about how people behave in real life. The researchers acknowledge the study didn’t account for other factors which can cause cancer, like age and obesity. And the potential for misinterpretation is something the researchers are also aware of.

“We must be absolutely clear that this study is not saying that drinking alcohol in moderation is in any way equivalent to smoking,” says Dr Theresa Hydes, lead researcher on the study.

“At an individual level, cancer risk represented by drinking or smoking will vary and for many individuals, the impact of ten units of alcohol (one bottle of wine) or five to ten cigarettes may be very different.”

So, depending on whether you’re a non-smoker or smoker, or how much you like a drink, reactions to today’s news may be different.

The average smoker in the UK smokes 11 cigarettes per day. And people who smoke are also more likely to drink. In that case, they may be smoking and drinking at the same time, which for some cancer types causes more harm than doing either one alone. Again, the researchers did acknowledge this.

Smoking is still worse

Smoking causes over four times the number of cancer cases that alcohol does in the UK. Using smoking as a risk comparison may also give the impression that people can substitute one risk factor for another.

“We don’t want people saying, ‘if I don’t drink that bottle of wine tonight, I can smoke 10 cigs instead’,” says Brown.

Brown also suggests there could be a risk of normalising smoking if it’s pitched against a behaviour that’s more socially acceptable.

“Improving understanding of other risk factors shouldn’t come at the price of reducing the perceived danger of smoking, because there’s no other risk factor that’s as bad as smoking.”

What do you think?

Not everyone who drinks alcohol will develop cancer. But when we look at the whole population, people who drink alcohol, even at low levels, are more likely to develop cancer than people who don’t. And that’s a really important thing for the public to know.

Finding sensible and informative ways of communicating cancer risk is extremely valuable and this study offers an interesting new way to try and put risk in context. But as is often the case with communicating health risks, it also shows how hard it can be. It’s likely that this research will get people thinking about the long-term effects moderate drinking can have on our health, and that’s definitely a good thing.

Professor David Spiegelhalter, Winton Professor of the Public Understanding of Risk in the Statistical Laboratory at the University of Cambridge, told the Science Media Centre: “If cigarette-equivalents were to be used to communicate the cancer risk of alcohol consumption, it is vital that their impact is properly evaluated to check they do not produce unreasonable concern.”

So maybe explaining cancer risk in this way is only useful if the public thinks it is?

We asked our followers on Twitter what they thought, and it appears they found the comparison useful.

But these responses still paint the overall picture of cancer risk as enormously complicated and incredibly nuanced. The researchers set out to answer ‘how many cigarettes are in a bottle of wine?’, which they did. How this number might now affect the way people view drinking remains to be seen.

Gabi