This morning, I read with satisfaction that the World Health Organization (WHO) thinks it’s OK for me to be drinking coffee. Indeed, “moderate” coffee consumption might even be good for me.
That’s nice to know, since I’ve had two cups already today. And at one time, people worried that coffee might be positively associated with colon cancer.
I thought this summary did a good job of reporting on current coffee meta-studies, differences amongst the underlying work, and the range of likely conclusions. The results are a mixed bag, depending on things like sampling bias, but most do say the association between coffee and cancer is at least not positive.
Health-related studies are a constant and avidly-consumed feature of news feeds. However when we interpret this information, our human wiring plays a role. We like to generalize (and we want to live). Reading about a possible association between coffee and good health, our brains can leap into action: “If I drink more coffee, I’ll be healthier!”
At some level, we know that isn’t what the study says, but what does it say? I find that it helps me to step through it. So, let’s assume the study applies to people of our general makeup and coffee-drinking habits – that’s not axiomatic, but let’s go with it.
Now, I imagine replicating myself 99 times, so there are now 100 of me, 50 enjoying coffee, and 50 doing without. The baseline rate for colorectal cancer is about six percent, and one study reported a 24% decrease in colorectal cancer incidence for those drinking at least four cups of coffee a day. That equates to an expected (but not guaranteed) incidence of 2.24 [(1-0.24)*0.06*50 ] for the 50 coffee drinkers, versus 2.95 [ 0.06 * 50] for the non-coffee drinkers, or a 1.4% difference.
That’s not zero, but very far from certainty (or even from 24%). Our natural bias can be to overreact – excellent for survival, but sub-optimal for processing facts. So our doctors will properly tell us what they always have: manage our weight, eat many vegetables, exercise, and stop stressing about things like the daily health report.
The health studies really are interesting – in part because this is one area where good and unbiased data are hard to come by, and as a result the outcomes are often unclear. I’ve often wondered – slightly tongue-in-cheek- whether the stress of trying to accommodate the recommendations of each statistical study negates the potential healthful benefits of following those recommendations. Now there would be a study I’d like to see.
Meanwhile, it’s bottoms up for the coffee cup- with the WHO’s blessing.