Health and Coffee Pt. 5: Coffee and Cancer

By Julianne Bierwirth, RD


In March of this year a California judge ruled that coffee sellers and coffee products in the state must warn customers that the beverage contains a chemical known to cause cancer. This ruling prompted a wave of confusion and concern that spread well beyond California’s borders. We at 1000 Faces fielded lots of questions along the lines of, ‘wait, isn’t coffee supposed to be good for you?’. According to the US government it is; the most recent USDA Dietary Guidelines for Americans recommended drinking coffee, up to 5 cups a day, for its role in reducing the risk of diabetes and heart disease.

The lawsuit resulting in the March ruling contended that coffee contains a chemical called acrylamide, a byproduct of the roasting process, and that acrylamide is a known carcinogen. It is true that coffee contains acrylamide and some public health organizations do classify it as a carcinogen. And yet the vast body of coffee research shows that, on the whole, moderate coffee drinkers are healthier, live longer, and have reduced incidence of things like diabetes, heart disease, and even cancer. This decision in California has been highly confusing to the public, so in addition to discussing the role of coffee in preventing many kinds of cancer, this article will define carcinogens and put acrylamide into perspective.

Carcinogens are substances that mutate a cell’s DNA in a way that signals that cell to go into a cycle of unchecked replication. We encounter countless types and qualities of carcinogens every day. Let’s take as an example the sun and its role in skin cancer. Sunlight is made of photons which are basically particles of energy. That energy can interact with the earth in many ways; initiating reactions that drive photosynthesis in plants, heating the planet, and causing our skin to form Vitamin D. Incidentally, the energy in these photons can also cause mutations to the the DNA of your skin cells.

Some people will sunbathe for years and never get cancer because, by sheer luck, their DNA never gets damaged in a way that causes cancer. Some people will never spend a moment in a bathing suit and will develop cancer because of their sun exposure walking to and from work. What we know is that the more sun exposure you get the more chance that sunlight has to cause the unlikely but devastating cancerous mutation. Sunlight is carcinogenic, and the odds of getting cancer from sunlight are directly proportional to the amount of sunlight you absorb.

Carcinogens as a whole are like this: they cause DNA damage and the more you are exposed to them the more often you are gambling with that damage being carcinogenic. There is a linear relationship: lower exposure equals lower risk, higher exposure equals higher risk. Logically, that means that any chemical that causes cancer, at any dose, is considered a carcinogen.


In practice the research looks like this: a mouse will be fed a chemical at a very high dose, say about 1000 times more than would naturally occur in its diet. If that mouse gets cancer more often than the control mice and this happens consistently enough study after study, then the chemical gets classified as a carcinogen. Unfortunately this means that the list of carcinogens expands rapidly to anything that can, at any unreasonable dosage, cause cancer. By this definition a great many things are carcinogens.

It is important to know that some chemicals are more carcinogenic than others - which is to say that a lower dose more often results in cancer. Aflatoxin, a chemical produced by a grain-loving mold in certain climates, is one of the most carcinogenic substances known to man. Parts of coastal China that are endemic for the growth of this mold have people and animals diagnosed with liver cancer at extraordinary rates. Mouse studies done with aflatoxin show that it takes a very low dose to cause cancer. Mouse studies done with acrylamide, however show that it takes an astronomical dose to cause cancer.

Acrylamide is formed inside the coffee beans when they are roasted above 250 degrees Fahrenheit. Its formation is the chemical result of starch and protein interacting at high temperatures - it is not added to the beans, nor is it a function of the brewing process. Coffee is not the only culprit - French fries and potato chips have the largest concentrations of acrylamide in our diets. It isn’t currently possible to roast coffee in a way that prevents the formation of acrylamide or to remove the acrylamide once the coffee is roasted. Unlike sunlight, acrylamide seems to offer no health benefit - only a potential health detriment.

Still, acrylamide, causes cancer in mice only at extremely high doses. An average sized human would have to drink the equivalent of about 2.6 million cups of coffee a day to get the 200 milligrams per kilogram body weight of acrylamide that has been shown to cause cancer in mice according to one study. In some research the results don’t even show an effect in mice at all. That isn’t to say there isn’t a risk, there possibly is, but acrylamide is certainly not a potent carcinogen like Aflatoxin. Some organizations, including the World Health Organization (WHO) do not classify it as a carcinogen at all. The American Cancer Society says they aren’t sure that acrylamide affects the risk of cancer in humans.

There are many chemical properties of the coffee we drink that seem to confer a benefit, including ones that decrease the incidence of cancer. These do not usually act by slowing cancer progression or repairing DNA damage, though there exist some molecules in nature that can work on that level. These antioxidants instead act to neutralize some carcinogens before they have a chance to damage your DNA.


In 2016, Nature, one of the most reputable scientific journals, published a statistical overview of 105 published studies on coffee and different types of cancer. Their analysis found increase in coffee consumption correlated with an increased risk for lung cancer but a reduced risk of oral, pharynx, liver, colon, prostate, endometrial cancer and melanoma. A 2017 review on coffee and cancer similarly concludes that there is, if anything, a mild benefit to drinking coffee.

In the light of these positive results it is worth stating that the vast majority of research looking at cancer risk takes the form of prospective studies. This means that researchers don’t assign individuals to groups of coffee drinkers and coffee abstainers and wait to see who forms cancer. This kind of trial would be both very expensive and take many years. Instead, they study the coffee drinking habits of people who develop cancer compared to those that don’t. There may be many other confounding variables that influence both coffee consumption and cancer risk, such as smoking status or ethnicity. The studies that exist aren’t perfect, but they are extremely encouraging.

So why did this California lawsuit move forward? The Council for Education and Research on Toxins (CERT), a public health advocacy group, sued the coffee industry seemingly as part of a larger effort to reduce the concentration of acrylamide in the American diet. CERT did the same years ago with potato products, suing fast-food companies over labeling on French fries. However, the law firm that represented CERT, Metzger Law Group, shares a mailing address with the advocacy group, driving curiosity as to the intentions of the suit. The ruling meant a substantial amount of money for the legal team involved. We’re not saying there’s a conflict of interest, but there’s a strong chance there’s a conflict of interest here.

In this case. the burden of proof was on coffee sellers to prove that acrylamide in coffee posed no significant risk. By the technical definition of a carcinogen and in accordance with California’s Proposition 65 - The Safe Drinking Water and Toxic Enforcement Act of 1986, the coffee industry was always going to have a rough go of defending themselves against this legal challenge. Some are suggesting that CERT and the Metzger Law Group are abusing the intention of Prop 65 for their financial gain and diluting its importance in clear and honest public health communication.

If nothing else, this ruling focuses very narrowly on one chemical component of the coffee, failing to take into account the health effects of coffee as a whole. No public health official would recommend abstaining from all sun exposure for fear of skin cancer. Years of research and thousands of studies have shown that, on the whole, coffee has a positive impact on health and longevity. Even if acrylamide causes cancer at very high doses, this is definitely a case of failing to see the forest for the trees.

Authors Note: as a scientist and dietitian, the Prop 65 decision in California as it relates to coffee is personally frustrating to me. Communicating scientific information to the public in a balanced and nuanced way is already very challenging. It is also the most important role of a scientist. When organizations, governments, or entities muddy the waters further by making claims that are factually true but irrelevant to the larger picture it confuses the public so that they no longer know which messages about health and safety are accurate and important. Some warning labels resulting from the 1986 Prop 65 decision convey a genuine and significant risk. If the label stays up for coffee and individuals (in my opinion) rightfully disregard it, that disregard may extend to all Prop 65 warnings, weakening its power as a public health communication tool.



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