Holy coffee, Batman! Guess what’s been the highlight of nutrition news this week? Yup, it’s coffee. And don’t get me wrong, I am a huge fan of this beverage, but is it really going to make me live longer?
This hubbub stems from two studies (here and here) published this week in the Annals of Internal Medicine looking at the associations between coffee consumption and mortality. Specifically, these studies suggest that drinking coffee reduces overall mortality. Unsurprisingly, the overwhelming media coverage focused on the results and published stories touting how drinking coffee will lead to a longer life. Now before you start chugging down the largest cup of coffee you can find, let’s take a look at the actual nuts and bolts of the study.
How were these studies designed?
Both studies used data from large prospective cohort studies. One study, “Coffee Drinking and Mortality in 10 European Countries,” used data from 521,330 participants ages 35 and older who were enrolled in the European Prospective Investigation into Cancer (EPIC) study. The other study, “Association of Coffee Consumption with Total and Cause-Specific Mortality among Nonwhite Populations,” was conducted with data from the Multiethnic Cohort (MEC), which included 185,855 African Americans, Native Hawaiians, Japanese Americans, Latinos, and whites ages 45 to 75 years of age living in Hawaii and Los Angeles.
Essentially, participants in both studies answered questions at baseline (via surveys or in-person interviews) to assess their education level, smoking, health status, height, weight, and typical coffee consumption. Then, over the next 16 years, the research teams tracked mortality rates and cause of death in these cohorts using local and national records.
What did these studies find?
These are two of the first studies to examine the associations between coffee consumption and mortality in large cohorts of European and nonwhite populations. In addition, both studies found that higher consumption of coffee (i.e. 2 or more cups a day of caffeinated and decaffeinated coffee) resulted in a lower risk of death by the end of the study.
Were there any limitations to these studies?
As with the majority of scientific research, there were some significant limitations. Both were observational studies, so these data cannot demonstrate that coffee prevents mortality. As we’ve discussed before, observational studies often represent a first step in scientific research, because they help establish associations that further studies can delve into and possibly figure out why the association(s) is there.
In addition, these studies assessed coffee consumption only once. It’s quite possible that some study participants stopped or started drinking coffee during the 16 years that followed. It’s also possible that some participants may have increased or decreased the amount of coffee they drank.
However, the most notable limitations in these studies start showing when you take a look at the actual data from the study, expressed as hazard ratios and confidence intervals. Observational studies will routinely use these statistics to examine the relationship between variables. In this pair of studies, the hazard ratios and confidence intervals were not particularly notable, revealing that coffee consumption decreased the risk of mortality by very small, amounts.
What’s the bottom line?
Despite some of the conversation and coverage around this set of studies being a bit hyperbolic, if you are a coffee lover, then you have another (small) reason to enjoy your cup o’ joe. Moreover, these studies are in alignment with the recent 2015-2020 Dietary Guidelines (DGA) recommendations that “moderate coffee consumption (3 to 5 cups/day) can be incorporated into healthy eating patterns”. Basically, if you drink a moderate amount of coffee (up to 400mg of caffeine), and you enjoy it, please do! Just don’t think that it is going to magically extend your life.
Julie Hess, IFIC ‘s Sylvia Rowe Fellow contributed to this article.