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Should your morning coffee come with a cancer warning?

Joseph Wu on what a recent ruling on coffee and cancer shows about how we make judgments about risk.

A California judge recently ruled that coffee sellers such as Starbucks are required to brand their beverages with cancer warning labels. The culprit? A chemical called acrylamide, a by-product produced when coffee beans are roasted.

Acrylamide is listed by California as a chemical the state considers to cause cancer. A nonprofit took the coffee industry to court, citing a California law that requires warnings when known carcinogens are present.

The ruling to put cancer warnings on coffee has brewed controversy. Stepping back, the discussion has revolved around two issues, one scientific and the other ethical. Oddly enough, there may not be a sharp division between the two.

First, does the scientific evidence sufficiently support the claim that ‘acrylamide causes cancer’? When mice are given levels of acrylamide 1,000 to 10,000 times higher than that present in human food, the incidence of cancer increases. But with respect to humans, some claim there is no conclusive evidence that coffee causes cancerOthers make a slightly different claim: it is not yet clear if acrylamide affects cancer risk.

Even if these scientific uncertainties could be resolved, there is a second issue: is this a good policy, all things considered? Scientific evidence alone cannot resolve this question. Even when there is consensus about what the evidence indicates, the scientific facts are compatible with a spectrum of different policies. We know that smoking causes lung cancer, but it is less clear whether we should do nothing in order to respect freedom of choice, ban tobacco indoors, or ban tobacco both indoors and outdoors in certain public spaces.

This is because there will always be a gap between the evidence and policy, one that must be filled with value judgments - choices that cannot be decided solely by evidence and logic. Good policies are not just logical extensions of the evidence.

Consider two different policy approaches to cancer warning labels. On the one hand, you might want to add a warning because you think consumers should be informed of the potential risk of cancer, even if the evidence is unclear. On the other hand, you might think that adding the warning label needlessly induces anxiety, which is not in the public interest.

Whichever policy approach you prefer, notice one interesting feature: the available evidence has not changed. In choosing between the policies, the reasoning was ultimately an ethical one: how should our obligations to warn the public of a potential cancer risk be balanced against the likely harms of the policy?

Value judgments

Interestingly, these ethical considerations are not merely secondary to science, but may themselves shape the scientific process. To see why, consider that we often do not have complete certainty for scientific claims. We have better or worse evidence that provides better or worse support for a theory. When making a scientific claim, then, we must decide: is the evidence enough to claim that coffee causes cancer?

Where we set this threshold for evidence, however, depends on social and political values. What are the consequences of putting cancer warnings on coffee, if it turns out the acrylamide exposure is safe? What are the consequences of not putting cancer warnings, if coffee does increase cancer risk? How we value these consequences influences how much evidence is enough to consider ‘acrylamide causes cancer’ as adequately established for policy.

Shouldn’t we simply acquire more evidence to inform our decision? Unfortunately, policymaking often cannot wait until the evidence comes in. And collecting good scientific evidence may be unfeasible or unethical. We could never test whether acrylamide raises cancer risk in a randomised controlled trial with human subjects.

In his ruling, Judge Elihu Berle said the coffee industry failed to show that the benefits of drinking coffee outweighed any risks from acrylamide. At first glance, this is a scientific issue: what evidence is there for the benefits of coffee and the harms of acrylamide? But it is also an ethical issue: whether we have enough evidence for a scientific claim depends on the consequences of being wrong; and whether the policy is a good one depends on how we value its likely benefits and harms. So, should your morning coffee come with a cancer warning? That depends on the facts, of course, but also values.

*Joseph Wu [2016] is doing a PhD in the History and Philosophy of Science. Picture credit: Wikimedia commons and Julius Schorzman.