23 Apr 2018

Fransplaining Science: So will coffee give me cancer now?

10:59 am on 23 April 2018

Coffee now carries a cancer warning in California. So will my daily cup of joe kill me?


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Photo: Tyler Nix / Unsplash.

In our new weekly column, Fransplaining Science, biochemist Dr Frances-Rose Schumacher explains science.

Late last month, when I was reading through my old local paper, the SF Chronicle, a headline jumped out at me: “California judge says coffee needs cancer warnings”.

Damn it, no way! I thought.
One of the first things I do every morning is make a coffee. Often I drink it quite fast, without really thinking about much, other than perhaps whether or not I’ll have a second cup. Other mornings, especially if I wake up determined to have a ‘super healthy day’, I sip my black coffee feeling a little bit virtuous, thinking how the caffeine will boost my metabolism and maybe mean I burn a few extra calories throughout the day.

I certainly didn’t want my first drink of the day to be littered with guilt that I may be slowly killing myself.  

I reflect on my morning coffee as a legit healthy option, due to the antioxidants that the brewed bean contains. Antioxidants are molecules that can ultimately ‘soak up’ potentially-damaging oxidants within your body (more on that another day!). I also know that coffee intake has been found to be inversely correlated with Alzheimer's, Parkinson's disease and some cancers - meaning it may somehow, either directly or indirectly, protect us against these diseases (these studies come with major caveats - more on that another day too.)

A proposition 65 warning at Starbucks

A proposition 65 warning at Starbucks Photo: Samantha and Arie / Flickr.

After I read the SF Chronicle article aghast, I set about reading some of the original research. I wanted to understand the reasons behind the headline. 

But before we go into that, here’s a bit of background for you: California is is a heavily regulated state. People can sue almost anyone for almost anything. Because of this, loads of effort goes into reducing liability and clearly defining responsibility. So you know who to sue if something goes wrong. 

In 1986, a law was passed, which aimed to increase public awareness surrounding the presence of chemicals that can cause cancer, birth defects, or reproductive harm.  Under the law, substances are added to a list if, for example, they are thought to cause at least one additional case of cancer in 100,000 people over a 70 year period.  

On first hearing about this law - known as Proposition 65 - I thought it was a brilliant idea; inform people to enable them to make choices surrounding their health and well-being! We have warnings about the dangers of cigarettes and alcohol in NZ, how could warning people of other dangerous chemicals be a negative thing? 
Proposition 65 works by placing a burden of responsibility on anyone who employs 10 people or more.  If a space - like a workplace or mall - is known to contain a substance found on the ‘substance list’, then a clear warning must be placed. This has resulted in warnings nearly everywhere.  When I first moved to San Francisco, I was alarmed by the presence of these signs wherever I went; my workplace, the mall, the movie theatre, any office block, there’s even a Prop 65 sign at Disneyland.  

A proposition 65 warning

A proposition 65 warning Photo: Tony Webster / Flickr.

Acrylamide is one of the hundreds of chemicals on the list. It’s often used in vast quantities in the manufacturing industry (paper, oil, textiles) and in 2002 it was unexpectedly found to be present in very low amounts in numerous cooked foods. Acrylamide is formed when naturally occurring sugars and amino acids are heated, so it’s present in baked starchy foods like chips, roasted beans, and basically anything toasted, roasted or browned. When coffee beans are roasted, some acrylamide is produced - hence the headline.

In 2010, a battle in the California courts began when a non-profit group filed a suit against Starbucks and several other large coffee chains in the USA. The group charged that the companies sold coffee containing a chemical - acrylamide - known to the state to cause cancer. 

Starbucks et al, argued that the levels of acrylamide produced by the roasting process was not significant enough to warrant a Prop 65 warning, but at the end of March this year, the judge ruled in favour of the non-profit, as the coffee companies were unable to prove that the consumption of their product did not result in one-excess case of cancer per 100,000 people exposed.  

So, what does the research say about all this? 

Studies that caused acrylamide to be deemed a “probable human carcinogen” were performed in rats, which were force-fed excessive amounts of the chemical in liquid form.  And by excessive amounts, I’m not talking double or triple, but more likely 1000 to 10,000 times higher than a maximal human exposure from all foods and drinks containing acrylamide.  

The rats who exhibited detrimental effects were dosed with 2.0 mg/kg/day, while the WHO estimated in 2001 that the highest dose a human is likely exposed to per day is 0.0008 mg/kg/day.  

There are only limited studies performed in humans (the studies estimated levels of naturally occurring acrylamide in their diets) and none of them found evidence that those who consume higher levels of acrylamide have an increased risk of cancer.  

There are two important things to note regarding these human studies, firstly they rely on people being extremely honest about what they eat and drink. Secondly they have all had limited power, meaning they would be unable to detect any very small increases in tumour incidence. 

Given all this evidence, I have come to the conclusion that we should not be too concerned with the acrylamide we are consuming by drinking coffee, or even eating a bag of salt and vins (which don’t have a Prop 65 warning on them) and fried food every day.

Some cooked foods contain naturally occurring acrylamide

Some cooked foods contain naturally occurring acrylamide Photo: Charisse Kenion / Unsplash

Avoiding fried foods is likely a good idea - not so much because of the acrylamide levels these foods contain, but because of the calorie burden fried foods carry. 

It’s unrealistic that any person could consume the extremely high levels of acrylamide that are likely dangerous (unless they sourced liquid acrylamide from industry - please DO NOT DO THIS). But to be on the safe side, don’t eat that burnt toast, ok? 

On a personal note, I’m very happy I can continue to have my morning coffee without fear.