September 5, 2015

Coffee and cancer, a translation

Image: Izabela Latak
During cancer treatment I started drinking coffee, through my mouth. That’s an important distinction in the cancer world because many people with cancer consume coffee through another hole in their body – the bum (more on that in a moment).

Once someone gets cancer they develop a radar for things that will help them stay alive. Some of these things come from doctors and some from family and friends, but the bulk of Things That Will Save You come from people who have written popular books, blogs or invented diets and ‘cancer-busting’ treatments.

Coffee is one of the most commonly suggested and debated of the Things That Will Save You. Cancer doctors don’t have much to say about coffee, but the complementary and alternative medicine field is full of ways to use coffee – one of which is pouring warm black coffee into your bottom, holding it there for a little while and then letting it drain into the toilet.

There is no evidence that drinking coffee through your bum has any effect on cancer. But there is evidence that drinking coffee through your mouth may.

A study recently made headlines when it found that drinking (through the mouth) four cups of coffee (or more) per day can drastically reduce the chances of colorectal cancer coming back. People that drank this amount of coffee were also less likely to die from their cancer.

The curse of having studied science before cancer and now studying medicine after cancer means I can’t just go with the news headline, dress like George Clooney and buy a Nespresso – I need to look at the details.

If this study was about eating 2 bananas a day, or sipping a shot of apple cider vinegar each morning, I probably wouldn’t bother – but 4 cups of coffee per day is a serious commitment and if I am going to expose my brain and heart to that amount of caffeine I need to understand the benefits.

So, for those of you that avoid dense scientific studies, here’s a translation on what you need to know. 

The journal: Journal of Clinical Oncology. This is a good journal which only publishes the top 10% of papers sent to it.

The main author: Dr Charles Fuchs, Director of the Gastrointestinal Cancer Center at the Dana-Farber Cancer Institute.

Why study coffee and colorectal cancer?
Image: Daniel Schwen
The logic is:
A. Coffee protects against Type 2 Diabetes.
B. Type 2 Diabetes involves high sugar and high insulin in the blood.
C. Colorectal cancer likes high insulin and high sugar in the blood.
D. If coffee works against Type 2 Diabetes it may also work against colon cancer.

How was this study done? This study did not start off by looking at coffee. The researchers have pooled a previous big clinical trial that compared [5FU + leucovorin] with [5FU + leucovorin + irinotecan] in people with stage III colorectal cancer. Because there was no difference in the outcomes after either chemo the researchers are able to chuck both groups together into one big database and ask different questions about people with stage III colorectal. They are tracking the people from the original study over time, so they know when they die or get sick again.

How did they measure coffee? They gave people a survey about foods and eating patterns halfway through chemo and then 6 months after chemo was finished. They then tracked these people over time. The average time of tracking was 7 years.

What did they find? They compared the number of cups of coffee consumed each day and whether someone's cancer came back and whether they died from their cancer.

They analysed the data two ways. In the first way they looked at people who drank 0, <1, 1, 2-3 and 4 cups of coffee or tea per day and measured when their cancer came back or if they died from their cancer. This showed that ANY coffee helped, and people that drank 4 cups a day had the greatest chance of survival.

In the second way they grouped everyone into two groups (no coffee per day vs 2 or more cups per day). This also showed that all the people who drank 2 or more cups per day had a greater chance of survival.

Couldn't something else explain this? Yes, maybe. This is not a randomised controlled trial (the gold-standard in medical research) so it can't say that coffee is the reason those people lived longer and had less cancer recurrence. But, the authors did control for HEAPS of factors that they know affect colorectal cancer recurrence and survival (BMI, sugary drinks, age, gender, lymph node involvement, a Western diet, exercise, chemo and smoking).

Because the research took all these factors into consideration, they are able to say: When you compare two overweight smokers who drink a lot of Coke and don't exercise, the one that drinks coffee will have a lower chance of dying from their cancer. You could pick any of the factors they 'controlled for' and make similar comparisons.

Gimme the nutshell: The study has 1000 people in it with stage III colorectal cancer, but the numbers of people in each group of coffee drinkers are much smaller, and in the ‘4 cups per day group’ the total number of people is only 62. The protective effect of coffee is dose-dependent, which means any coffee is good and 4 or more per day is best. This is a correlation, not causation, and the authors admit there may be another factor responsible for the pattern they found. The pattern they found is a strong one though and the Journal of Clinical Oncology is a robust and well-respected journal.

In a New York Times blog about this study (the best reporting of the study that I found), the main author says that patients shouldn’t start drinking coffee because of his study, but, “If you’re a coffee drinker and enjoy it, stick with it”. For coffee-haters he suggests adopting Things That Will Save You where the evidence is clear-cut: “avoid obesity, exercise regularly and follow a balanced diet.”

What's going on with coffee? Science doesn't know yet. It could be that coffee makes cells in the body less sensitive to insulin. It could be that coffee works as an antioxidant. It could be that coffee is anti-inflammatory.

Where was tea in all of this? They didn't classify types of tea consumption - just herbal and non-herbal. No mention of green tea. This is the US and I suspect tea is not as common a part of their diet as it is in ours.

Is it coffee or caffeine that is important? The decaf coffee consumed by the cancer survivors in this study had no effect on survival. Only actual coffee did.

So, my thoughts after reading this are that I like coffee and will keep drinking it. If I didn’t drink coffee and wanted to start I would print off the study (or at least the abstract) and take it in to the next appointment with my GP or oncologist and get their opinion.


  1. Nice post.. I happened to read to a post about colorectal cancer at CSCS ( website .. There is a lot of useful information posted here