Welcome to Bad Science on the Internet! Here, we highlight some of the crazy and sometime dangerous stuff people post online, and then we give you the facts.

The Bad Science:

There have been a number of recent news stories about the possibility of coffee being listed as a human carcinogen in the state of California. A recent court decision ruled against several coffee sellers (including 7-Eleven and Starbucks), allowing a lawsuit to continue that may end with coffee being listed as containing potential carcinogens in California. How did this happen, and should we be worried about our morning brew? Let’s break down the science and find out.

Coffee does not cause cancer.

Let’s start here. There is absolutely zero data to suggest that drinking coffee increases your cancer risk. In fact, it is more likely to be protective against some cancers because of the antioxidants it contains. Coffee may also lower the risk of heart disease and diabetes, though the data supporting these potential positive health effects is weak. It is true that the International Agency for Research on Cancer (IARC) classified drinking very hot beverages of any kind as being linked to cancer, but this is not specific to coffee and is honestly kind of silly, because most people intuitively understand that scalding their esophagus and mouths with hot beverages day after day is probably not good for them. So to recap: coffee does not cause cancer, do not drink boiling water.

California’s Proposition 65 is a well-intentioned risk communication statue with silly labeling requirements

Proposition 65 (or Prop 65) is a California law that was passed in 1986 as a ballot initiative, meaning that a group of citizens got enough signatures to propose a new state law, and that proposed law appeared on the ballot during the next statewide election. Since the majority of Californians voted to approve it, the proposal became law. The idea behind Prop. 65 was most certainly a noble one: to prevent people and businesses from releasing chemicals that may cause cancer or birth defects into water, and to require businesses that use these chemicals to label them so their employees and customers are aware that they may be exposed to them. It all makes great sense.

The problem with proposition 65 mostly comes from that last clause – the requirement to label everything – and they really mean everything – that could cause cancer or birth defects. This is a problem because, as scary as it may sound, cancer- and birth defect-causing chemicals are everywhere, and so a whole bunch of stuff needed to be labeled. What’s on the list? Glad you asked!

First, there are a lot of dangerous chemicals you might expect on the list – classic carcinogens like benzene and dioxins, and teratogens like lead and valproic acid, plus pesticides and dangerous solvents. But also included are a large number of common drugs, including aspirin, Tylenol, statins, ACE inhibitors, benzodiazapines, antibiotics, anti-virals, and oral contraceptives. Some of these make sense, but many are on the list because of weak evidence and/or very low risk of cancer or birth defects. The labels of these drugs already spell out these risks – so why does the pharmacy also need a sign saying that it contains potentially dangerous substances behind the counter? How is that helping anyone?

On top of these, there is a whole bunch of things on this list that people are exposed to everyday – often whether they mean to or not. Ethanol, vitamin A, aloe vera extracts (apparently a cancer risk?), carbon monoxide, carbon dioxide (!), gasoline vapors and diesel exhaust, used engine oils, soot, salted fish, tobacco and tobacco smoke, wood dust, nitrous oxide (“laughing” gas), really small particles of sand. I swear I didn’t make any of those up. Your body literally produces carbon dioxide and vitamin A (should we label ourselves?), and the vast majority of people in California (and most of the developed world) are exposed every day to gasoline vapor, ethanol, and diesel exhaust.

So why bother labeling all of these things? If you have ever lived in or even visited California, you’ve seen the Prop 65 signs. They are everywhere – at the gas station, pretty much every business that uses cars/trucks, the pharmacy, your dentist’s office, research labs, and now maybe coffee shops. The signs simply say that the business in question uses “chemicals known to the state of California to cause cancer or reproductive effects,” but there is no requirement to actually list the potentially dangerous chemicals, define how much of them may be laying around or describe what procedures are in place to protect people. If the point of the labeling clause of the law was to inform people, mission accomplished. If the point was to allow people to weigh their risks and make informed decisions, complete and utter failure has been achieved.

There are low level of chemicals known to cause cancer in coffee

There are over a thousand chemicals in a typical cup of coffee. With out question, at least 2 of them (and maybe a third) are on the prop 65 list, and probably more. The first one is caffeic acid, which is on the list because of a link of cancer, Caffeic acid is found in a wide variety of fruits and vegetables in addition to coffee. IARC has classified it as a possible human carcinogen based on data in mice and rats. Since caffeic acid has been on he list since 1994, it’s not entirely clear why coffee hasn’t been considered for labeling before. In addition, California is considering placing caffeine on the list! It is currently in the “under consideration” category for reproductive toxicity. Certainly, if caffeine ends up confirmed to the list, it seems like all caffeinated beverages could end up labeled, despite that fact that there is pretty much no data suggesting that caffeinated beverages actually cause birth defects in humans.

Despite the presence of caffeic acid and (potentially) caffeine on the prop 65 list, the real issue right now is the third chemical form coffee on that list – acrylamide. There is a lot more data on acrylamide than caffeic acid – it is listed as a probable human carcinogen, and unlike caffeic acid (which induced tumors in animals, although the mechanisms for this aren’t clear), we know that acrylamide interacts directly with and damages DNA, a hallmark for many carcinogenic compounds. Acrylamide is produced at low levels when coffee beans are roasted, and there is little doubt that people are going to drink some amount of acrylamide when they drink their coffee. A typical fresh-roasted cup of coffee contains less than a microgram of acrylamide. These levels are many times lower than the levels shown to be toxic to animals.

So if coffee contains caffeic acid and acrylamide, why doesn’t it cause cancer? There are many possible reasons for this. It could be that it does increase the overall risk for cancer slightly, but the risk is too small to measure or is over-shadowed by the larger decrease in cancer risk associated with the antioxidants in coffee. It could also be that these cancer-causing chemicals are not absorbed from the coffee and therefore do not get into the body to cause toxicity. The most likely explanation is just that there isn’t enough of it. The amount of caffeic acid and acrylamide in coffee is way below the doses studies in animals, and as we all know, the dose makes the poison.

In addition, it turns out that, acrylamide is in more than just coffee! It is formed whenever plant products are cooked at high temperature – it’s found in potato products (like French fries) and other cooked grain products. In California, restaurants that serve fries have to display a prop 65 label because of the acrylamide in this food.

So the recent series of lawsuits and push to label coffee products should really not be surprising given the history here. We have known for a long time about the low levels of acrylamide in coffee, just as we have known that there is caffeic acid and caffeine in there, too. The labeling of french fries came about after successful lawsuit from the California attorney general, and it seems like the current lawsuit will succeed as well – at least it will succeed in forcing the labeling of coffee as containing chemicals known to the state of California as potentially causing cancer.

What’s the bottom line?

The consumer group involved in the current coffee lawsuit in California is the same one that filed the initial lawsuit over acrylamide in french fries. They appear to be acting in good faith here, though unlike french fries (not a particularly healthy food), coffee probably has a net positive effect on human health. So their efforts aren’t likely to improve people’s health by convincing them to avoid coffee. However, their efforts are still important. While many will focus on the labeling required by inclusion on the prop 65 list, the real win for consumer safety will come from the tracking and potential reduction of acrylamide in coffee that may (hopefully) come from this legal action. It is undoubtedly a good thing to reduce the levels of acrylamide in our food when possible. It may not be causing cancer, but it’s certainly not providing any benefit.

The downside to this is that the well-intentioned but silly prop 65 labeling law will plaster Starbucks all over the state with signs telling people that coffee is dangerous. Most will ignore these signs, and some will over-interpret them and quit coffee all together. The problem is that these signs tell us nothing about the level of risk we face when drinking coffee. The science is clear on this – there is no significant cancer risk form drinking coffee. If you want to reduce your cancer risk, the best things you can do is avoid the sun and tobacco products – avoiding coffee will probably just make you grumpy.