Alcohol-cancer link is not as scary as it seems

The headline had some of my friends in a panic. Citing evidence, the American Society of Clinical Oncology warned that even light drinking could increase the risk of cancer.

Once again, we’ve been told that something we eat or drink is going to kill us. Once again, we’re provided an opportunity: A more nuanced discussion of risk — and how we communicate it — can leave us much happier, and perhaps healthier.

Let’s begin with the fact that it’s easy to use studies to talk about cancer. Nothing illustrates this better than the classic 2013 study that examined research on 40 common ingredients selected from an ordinary cookbook. Researchers found 264 different studies touching on at least one of those ingredients. Their conclusion? Depending where you look, you can find evidence that says that nearly everything we eat is both associated with higher rates of cancer and lower rates of cancer.
 

The gist of the oncology society announcement is that there is a reasonable amount of evidence finding an association between some cancers (specifically oropharyngeal and larynx cancer, esophageal cancer, hepatocellular carcinoma, breast cancer and colon cancer) and alcohol. It acknowledges that the greatest risks are with those who drink heavily, but it cautions that even modest drinking may increase the risk of cancer. In the United States, the announcement also notes, 3.5 percent of cancer deaths are attributable to alcohol.

Of course, this means that 96.5 percent of cancer deaths are not attributable to alcohol. If we eliminate heavy drinking, which no one endorses as healthy and where the association is surest, that number climbs. If we also eliminate those who smoke — smoking is believed to intensify the relationship between alcohol and cancer — the number of cancer deaths not attributable to alcohol approaches 100 per cent.

Let’s stipulate that there may be a correlation between light or moderate drinking and some cancers. We still don’t know if the relationship is causal, but let’s accept that there’s at least an association. For breast cancer — which is the cancer that seems to be garnering the most headlines — light drinking was associated with a relative risk of 1.04 in the announcement. Relative risk refers to the percentage change in one’s absolute (overall) risk as a result of some change in behaviour. (And 1.04 is a 4 per cent change from 1.0, which represents a baseline of no difference in risk between an experimental group and a control group.)

A 40-year-old woman has an absolute risk of 1.45 percent of developing breast cancer in the next 10 years. This announcement would argue that if she’s a light drinker, that risk would become 1.51 per cent. This is an absolute risk increase of 0.06 per cent. Using what’s known as the Number Needed to Harm, this could be interpreted such that if 1,667 40-year-old women became light drinkers, one additional person might develop breast cancer. The other 1,666 would see no difference.

Of course, moderate or heavy drinking might increase the risks further. The absolute risks for that 40-year-old would go to 1.78 per cent from 1.45 per cent for the moderate drinker, and to 2.33 per cent for the heavy drinker. Those numbers are still not that scary. But maybe any increase in risk is too much for you. That’s fine. 

If you’re one of those people, though, you have to acknowledge that you can’t look at any one cancer in a vacuum. 

A person can get almost any cancer.

The large meta-analysis upon which this announcement was based looked at 23 types of cancer with respect to alcohol consumption. It found a harmful relationship between three of them and light drinking. But it also found protective relationships — meaning a decreased risk of cancer — between six of them and light drinking.

I’m not arguing that you should engage in light drinking to avoid those six cancers. I’m merely pointing out that cherry-picking allows you to come to different conclusions. With respect to moderate drinking, there were harmful relationships with seven cancers and protective relationships with three. The announcement focused on the former, not the latter.

A 2013 meta-analysis in the Annals of Oncology that looked at all cancers found that, over all, light drinking was protective; moderate drinking had no effect; and heavy drinking was detrimental.

It’s even cherry-picking to focus only on cancer, though. A person can get any number of diseases, and this fact makes the dangers of light and moderate drinking even muddier.

If you accept the methodology of case-control and cohort studies, from which many of the links between alcohol and cancer arise, you have to accept the results of similar studies of other diseases. For instance, a cohort study of about 6,000 people found that those who drank at least once a week had better cognitive function in middle age than those who didn’t. A 2004 systematic review found that moderate drinkers had lower rates of diabetes (up to 56 percent lower, although that’s a relative risk reduction).

Randomised controlled trials of alcohol (they do exist) show that light to moderate drinking can lead to a reduction in risk factors for heart disease, diabetes and stroke. These protective factors may be greater than all the other negative risk factors (even cancer) that might be associated with light or moderate drinking. More women die in the United States of heart disease than cancer. So do more men.

Moreover, dire warnings have consequences. I know far too many people who now throw up their hands at every news story because it seems as if “everything” causes cancer. These stories rarely acknowledge an alternative point of view. The absolute risks of light and moderate drinking are small, while many people derive pleasure from the occasional cocktail or glass of wine. It’s perfectly reasonable even if a risk exists — and the overall risk is debatable — to decide that the quality of life gained from that drink is greater than the potential harms it entails.

This is true for many, many foods, not just alcohol.

What can we do about this? We could make simple changes to have a better understanding of risk so that each new proclamation doesn’t send us into a tizzy:

1) Consider the absolute risks. A 30 percent increase in risk sounds scary, but an increase from 1 percent to 1.3 percent absolute risk does not, though these are the same things. Likewise, we should be more concerned about a 5 percent risk increase to 21 percent from 20 percent than about a 30 percent increase to 1.3 percent from 1 percent.

2) Don’t give too much weight to observational data. This is especially true when causal data are available.

3) Don’t focus on any one disease while ignoring others. Something may be harmful regarding one disease while beneficial regarding another.

4) Don’t cherry-pick. That is, don’t focus only on some studies, or only on some results. Review all the evidence for the most holistic picture possible.

5) Acknowledge the harms, as well as the benefits, of recommendations. Consider both cost and joy.

These rules may not make for exciting headlines. They may, however, lead to happier, and perhaps healthier, lives.

© 2017 New York Times News Service