In the coming months a judge in California will decide whether coffee should be listed as a possible carcinogen throughout the state. The court decision is the result of a 2010 lawsuit brought by an NGO, the Council for Education and Research on Toxics, against the biggest coffee sellers charging that the presence of trace amounts of a chemical pose a threat to the health of coffee drinkers.

The chemical in question is acrylamide, which is formed when coffee beans are roasted. Under California’s Proposition 65, businesses must notify the public if a product contains any of the 65 chemicals that have been linked to adverse health effects, including cancer and reproductive abnormalities.

Coffee is only the latest example of a trend that has become all too common. Activists who profess concern for human health and the environment latch on to an isolated finding – in this case the presence of trace amounts of a contaminant in coffee – and proceed to mount a well-orchestrated campaign to protect the public from the theoretical threat. In the process they use the issue to raise their profile and solicit funds. Similar campaigns have involved the herbicide glyphosate and genetically-engineered crops, BPA, and other substances.

The distinguishing feature of these campaigns is that they isolate a factoid from its scientific context and use it to instill fear in the public and to give bureaucratic regulators a new threat to regulate.

In the case of coffee, what is most egregious and problematic is that, while focusing on trace amounts of acrylamide in coffee and on the results of animal studies, the campaign ignores an abundance of solid evidence that has accumulated over decades concerning the health effects of coffee-drinking in humans. Even many commentators on this wrong-headed campaign fail to appreciate the weight of the epidemiologic evidence exculpating coffee.

 Presence of acrylamide in coffee and other foods.

In the early 2000s, the Food and Drug Administration undertook measurements of acrylamide in a wide range of foods and has published these data. The agency states that “Acrylamide is found mainly in foods made from plants, such as potato products, grain products, or coffee. .. Generally, acrylamide is more likely to accumulate when cooking is done for longer periods or at higher temperature.”

In response to the frequently asked question, “Should I stop eating foods that are fried, roasted, or baked?” FDA states, “No. FDA’s best advice for acrylamide and eating is that consumers adopt a healthy eating plan.”

It needs to be emphasized that acrylamide is measured in foods in units of parts per billion (ppb). This measurement is the mass of a chemical or contaminant per unit volume of water. To give an idea of what 1 ppb means, one drop of ink in one of the largest tanker trucks used to haul gasoline would be an ink concentration of 1 ppb. 1ppb= 1/1 billion = 0.000000001.

In the 2004 survey published by the FDA, levels of acrylamide in different brands of coffee prepared in different ways ranged from non-detectable to 609 ppb. Levels of acrylamide in cereals ranged from non-detectable to 534 ppb. Levels in cookies ranged from non-detectable to 1540 (Health Valley Original Oat Bran Graham Crackers). Levels in potato chips were the highest in any food group, ranging from 647 to 1970.

Rodent studies of acrylamide and cancer.

Animal studies have shown that acrylamide causes cancer in multiple organs in rodents, when fed at very high doses. On this basis, acrylamide was classified by the International Agency for Research on Cancer (IARC) as a “probable carcinogen” in 1994. What needs to be realized is that because of the extremely high doses used in these experiments and because rodent anatomy and physiology are different from human anatomy and physiology, these results are not directly relevant to the human situation.

Dietary acrylamide and human cancer.

A systematic review of studies that estimated dietary intake of acrylamide and its association with human cancer found that a majority of studies reported no statistically significant association between dietary acrylamide intake and various cancers, but a few associations were noted with several cancers. The problem with these studies is that it is difficult to accurately estimate an individual’s intake of acrylamide based on his/her reported usual eating habits.

In view of the limitations of the types of studies described above, epidemiologic studies of coffee consumption in large cohorts assume enormous importance. Rather than attempting to measure acrylamide, they assess the occurrence of cancer related to coffee intake itself. As I will argue, these studies provide the best and most relevant evidence we have relating to acrylamide as a carcinogen at the levels at which it is actually consumed in coffee.

Human – that is epidemiologic studies – of coffee drinking habits and cancer.

We have impressive evidence addressing the possible health effects of coffee-drinking. This is because coffee-drinking is a habitual behavior that is relatively stable, and people can tell researchers with a fair degree of accuracy how long they’ve been drinking coffee and how many cups they usually consume per day.

Furthermore, coffee is consumed by a large proportion of the population in Western countries and, yet, importantly, there is a proportion of the population that does not consume it. Among consumers, there is a wide range in the number of cups of coffee consumed. Thus, coffee consumption is amenable to study with respect to an individual’s exposure (present or absent) as well as the dose among those who drink coffee. This means that, if coffee drinking were in fact associated with cancer, we would stand an excellent chance of detecting it.

Thus, information available on the association of coffee-drinking with cancer is of a similar order to the information that permitted us to conclude that cigarette smoking is associated with diseases including cancer of the lung, mouth, throat, bladder, and pancreas, as well as cardiovascular disease. This point can’t be emphasized too strongly. Information on coffee intake may even be superior to information on alcohol consumption, since some respondents are reluctant to reveal how much alcohol they actually consume, whereas there is less of a stigma associated with coffee.

The highest quality evidence from human studies comes from cohort studies carried out in the past two decades. In this type of study, a large population is enrolled, and information about the participants’ health and behaviors is collected at the time the study begins. The cohort is then followed for a number of years and monitored for the development of disease. This type of study design is not susceptible to the problem of recall bias, since information about exposure is collected prior to the development of disease.

Hundreds of studies of the association of coffee intake with various types of cancer have been published. The results of these studies have been summarized in meta-analyses to determine whether there is a consistent association of coffee drinking and cancer of a specific type.

What these meta-analyses and qualitative reviews show is that coffee drinking is associated with reduced risk of several cancers, including endometrial, colorectal, liver, and postmenopausal breast cancer. In the case of liver cancer, coffee drinkers have roughly a 50 percent reduction in risk. For other cancers, including bladder, kidney, prostate, pancreas, and ovary, there is no consistent evidence of an association.