I love my coffee, but it’s for the flavor and caffeine hit. I never thought of coffee as having many health benefits that could make me live longer. However, I ran across an article that might interest my fellow coffee drinkers — it seems like drinking moderate to large amounts of coffee reduce your risk of death. Not by a lot, but by a meaningful amount.
As I usually do, I will review the paper for you, give you the key data point, and then grade the paper. Again, coffee is not a miracle drink (though in the morning I think it is), but it seems to have some benefits.
Coffee health benefits paper
In a paper published on 1 August 2018 in JAMA Internal Medicine, Erikka Lotfield, Ph.D., Division of Cancer Epidemiology and Genetics, National Cancer Institute, and colleagues examined the relationship between coffee consumption and all-cause mortality in nearly 500,000 individuals. Although they focused on all causes of death, they also looked at mortality as a result of various cancers, cardiovascular diseases (including heart attack and stroke), and other diseases.
They also employed a genetic analysis examining whether genes influenced mortality while drinking coffee.
So here are the results that coffee drinkers are looking for
- 1 cup of coffee per day (1 cup equals 8 fluid ounces or 240 ml), there was an 8% reduction in mortality risk (risk of death).
- 2-3 cups per day, there was a 12% reduction in risk.
- 4-5 cups, also a 12% reduction in risk.
- 6-7 cups, a 16% reduction in risk.
- >6 cups, a 14% reduction in risk
The researchers found that as individuals drank more coffee, they appeared to die a little less frequently. They also found that this result was not changed regardless of the presence of genes that are associated with caffeine metabolism. And the reduction in mortality showed a dose-response relationship up to 8+ cups of coffee per day.
In addition, the researchers showed similar correlations for instant (note — who on earth drinks instant these days), ground, or decaffeinated coffee.
The researchers also found no reduction in risk for lung cancer, colorectal cancer, breast cancer, pancreatic cancer, cardiovascular disease, ischaemic heart disease, stroke, and respiratory disease. And they also found that the genes associated with caffeine had little influence over the results.
But do these results give us any indication of coffee’s health benefits? Let’s look at it from two different perspectives.
What don’t I like about this coffee health study?
The most important point is that it is an observational type of study. That is, it requires patients to remember how much coffee is consumed, and then attempt to correlate it to mortality. There are too many variables here, especially for such small effects on the risk of death.
Furthermore, observational studies have a fairly critical issue – it can be difficult to determine confounding variables, that is, a variable that can influence both the cause and the effect. A classic example of confounders is that ice cream consumption is strongly correlated with drownings – but the confounding variable is summer heat which increases both ice cream consumption and increased drownings (since pools, lakes, rivers and such are popular).
So increased ice cream consumption does not increase drownings, they are both affected by summer weather and really have nothing to do with one another.
It’s possible that healthier individuals drink more coffee and have a lower risk of all-cause mortality. Or individuals who drink more coffee exercise more. Or eat less. Or have less stress. It’s difficult to tease out confounders in these types of studies, thus making it really difficult to make any claims about coffee’s health effects.
It is theoretically practical to set up a study that controls for many of these confounders. But it is difficult to control them all, because you may not know what they all are. The ice cream example is easy, but trying to find all of the confounders for coffee may be impossible.
It’ll probably be difficult to actually show causality between coffee consumption and mortality. Coffee contains over 100 different chemical compounds, so if this study is an indicator that coffee reduces mortality, it’s going to take decades before we can determine which, if any, of those compounds have a beneficial health effect.
The authors themselves stated that “limitations include the study’s low participation rate, approximately 5.5%; consequently, the cohort is not demographically representative of the general UK population, with evidence of a “healthy volunteer” selection bias.”
What do I like about this coffee health study?
Epidemiological studies like this have more value with more data points. This study included a half million individuals, which makes it more powerful than taking a survey at your local Starbucks.
Second, the study did show a modest dose-response relationship. In any medical study, we would like to see a greater effect with a greater dose, and this study generally (though kind of weakly) shows that.
However, my scientific critique of this study is that it is underwhelming, but it does lead me to believe that there’s enough data to keep looking.
Summary
The authors concluded:
…coffee drinking was associated inversely with all-cause mortality, including in those drinking at least 8 cups per day, in both slow and fast metabolizers of caffeine, and in consumers of ground, instant, and de- caffeinated coffee. Our results are based on observational data and should be interpreted with caution. Nevertheless, these results provide further evidence that coffee drinking can be part of a healthy diet and may provide reassurance to those who drink coffee and enjoy it.
Despite the blaring headlines that say “Six coffees a day could save your life,” this study shows no such thing. But the article does provide some intriguing evidence that the more coffee you consume may reduce your risk of all-cause death. And that may be good enough.
Citations
- Loftfield E, Cornelis MC, Caporaso N, Yu K, Sinha R, Freedman N. Association of Coffee Drinking With Mortality by Genetic Variation in Caffeine Metabolism: Findings From the UK Biobank. JAMA Intern Med. 2018 Aug 1;178(8):1086-1097. doi: 10.1001/jamainternmed.2018.2425. PubMed PMID: 29971434.
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