Via NPR’s The Salt: How Many Cups Of Coffee Per Day Is Too Many?
That morning cup of Joe is a daily, practically sacred ritual for many of us. A large body of research has confirmed that a coffee habit is perfectly fine for most people, and may even have some health benefits – from fighting depression in women to lowering the risk of stroke and prostate cancer.
But is there too much of a good thing?
A study published this week in Mayo Clinic Proceedings suggests that when it comes to coffee, too much appears to be more than 28 cups per week, at least if you are under 55.
The researchers found that younger men who passed the 28 cup weekly threshold – which works out to about 4 cups per day – had a 56 percent increased risk of death from all causes. Younger women who were heavy coffee drinkers had a greater than two-fold increased mortality risk.
Ok, so what gives?
Lavie and his colleagues looked at more than 40,000 people, ages 20 to 87, who were enrolled as part of the Aerobics Center Longitudinal Study, a long-term study conducted between 1971 and 2002. The researchers followed up with the participants for 17 years on average. But they were only asked about their coffee consumption once – so, as Lavie himself notes, we don’t know how their coffee habits changed over time.
Another limiting factor: smoking. Heavy coffee drinkers in the study were more likely to be smokers – which makes sense, since the data was collected beginning more than 40 years ago. Van Dam thinks the research didn’t do enough to control for smoking. In fact, as we’ve previously reported, lots of studies in the 1980s failed to control for the link between coffee drinking and smoking, which is one big reason why early research appeared to give coffee a bad rep. Evidence suggesting health benefits from coffee began to emerge only as studies separated the two habits.
So, really, it doesn’t seem that one can draw coffee-specific conclusions from the study.
One thing I always wonder about in these studies, especially when based on survey data, is what constitutes a “cup”? Does it constitute an actual, 12 8* oz cup (as in the measurement) or is it whatever you happen to drink out of? I just finished a “cup” of coffee, but the mug from which I drank is well over 12 8 ounces in volume. And let’s not even get started about tall, ventis, shmentis, or whatever. If the goal is to link amount consumed to health outcomes, this would seem to be rather important.
The study itself does note the lack of follow-up measure of per cup consumption as well as no measure of coffee preparation methods as well as noting:
residual confounding may still exist even though we adjusted for all the potential confounders available in the present study. Smoking is likely to be one of the most important factors to cause residual confounding in this investigation.
I am not a stat guy, and I certainly am not versed in medical research (although it is amazing the degree to which this type of analysis is not all that different from a lot of what is done in the social science, since it is really survey analysis and not biological research).
It is worth noting that the study claims to have found an association, not a causal link. The value of the study is that it provides the basis for future research that would be able to address the questions left open. As such, I am not going to adjust my coffee consumption habits just yet. Granted, I like to drink coffee, so maybe I am suffering from a case of confirmation bias.
The article can be found here: Association of Coffee Consumption With All-Cause and Cardiovascular Disease Mortality
*Cleverly I illustrated the fact that most people do not self-operationalize “cup” properly.
