Category: Cardiology

I am an degenerate coffee addict. This has been so since I took my initial drink during my first chemistry finals as a college freshman. My coffee consumption hasn’t decreased much since then. I drink coffee because of its taste and the caffeine. Potential coffee health benefits are, personally, way down the list of reasons for drinking it. And frankly, I’m always skeptical of claimed health benefits for any food, unless there’s some really strong scientific evidence, which is generally lacking.

But recently, news outlets have been touting a couple of robust studies that seem to indicate that there are significant coffee health benefits. For those who know me, I rarely accept popular news sites analysis of scientific research. I think my loyal readers expect me to look at the science and see if there is any validity to the claims made by the press.

Claims about coffee health benefits and claims goes back centuries. It cured alcoholism. Coffee made you work longer. It was good for your heart. Drinking it was bad for your heart. It increases risks of some cancers. Wait, it decreases risks of some cancers. In other words, we really didn’t have vigorous evidence supporting anything definitive with respect to the drink’s health benefits or detriments.

It’s time to look at these two new studies and see what they tell us about drinking coffee.

Coffee health benefits – the first study

The first study we’re going to examine, from Gunter et al., published in the Annals of Internal Medicine. At a meta level, this epidemiological study was run by respected scientists, with the results published in a very high impact factor (17.2020) journal. Moreover, the study included around 520,000 participants in 10 European countries, which makes it one of the largest studies to date on coffee health benefits.

Compared to some of the horrifically bad studies that we have seen making outrageous claims about this or that food, drink or diet, this study is impressive. This is the kind of study that is equivalent to some of the best vaccine epidemiological research out there.

But what does the results say? To be blunt, they found that drinking more coffee would significant lower a person’s risk to all mortality.

The hazard ratio (HR), which compares the risk of dying between the coffee-drinking and non-coffee groups, was 0.88. In other words, there was a 12% reduction in all death causes in men who were in the upper quartile of coffee consumption. The HR for women in the upper quartile of consumption was 0.93, or a 7% reduction.

Frankly, a 12% or 7% difference in mortality is interesting and intriguing, but from a perspective of evidence-based medicine, it’s difficult to say this is clinically meaningful. However, if there are no known risks to coffee, which would have been uncovered by this study, the importance of those decreases in mortality become more substantial.

There were more significant results for certain diseases. The HR for coffee consumption and digestive disease mortality for men was 0.41 (a 59% reduction), and for women was 0.60 (a 40% reduction). Interestingly, for women, the HR for coffee drinking and circulatory disease mortality was 0.78 and cerebrovascular disease mortally was 0.70. However, the HR for coffee drinking and ovarian cancer mortality was 1.31, or a 31% increase.

The authors concluded, without much wiggle room:

Coffee drinking was associated with reduced risk for death from various causes. This relationship did not vary by country.

Review of the first study

Although the results appeared to fairly solid, I think it’s important to be critical of the results. First, we have no data that shows us whether or not coffee drinkers are just a healthier subgroup of people irrespective of their coffee drinking (they did separate out smokers from this study). Maybe coffee drinkers exercise more or eat less fats than the average person – these confounding factors have not examined carefully.

Second, like I discussed before, dose makes the poison, and dose also makes the medicine. Is there a level of coffee consumption at which point the risks outweigh the benefits? That’s not clear in this paper.

The best I could tell you from the data from this particular study of coffee health benefits is that if you’re a coffee drinker, maybe there is a slight decrease in risk of mortality, so keep on drinking. But if you don’t like coffee (yeah, there are those types around), or the caffeine effects of coffee are not to your liking, I’m not sure you should worry about suddenly taking up the habit.

Coffee health benefits – the second study

This second study, from Park et al., was also published in the Annals of Internal Medicine, once again, a very high quality journal. At a meta level, it’s as high quality as the study from Gunter et al., although this study looked at coffee consumption from a slightly different perspective.

Park et al. surveyed over 185,000 African-Americans, Native Americans, Hawaiians, Japanese-Americans, Latinos and whites, a broader ethic diversity than the first study. The researchers compared coffee consumption at various levels to a control group who drank no coffee. They adjusted for confounders such as smoking, age, alcohol intake, body mass intake, exercise, education and other factors.

For those who drank about 1 cup per day (in this case, they mean the English measurement of a cup, about 250 ml, not the standard “cup” in your local Starbucks which is about 500 ml), the HR was 0.88 or 12% reduction in total mortality. For 2-3 cups per day, the HR was 0.82. With consumption ≥ 4 cups per day, the HR was the same 0.82, or 18% reduction. All of these numbers were statistically significant.

Moreover, the researchers found that coffee increases longevity across various races.

Park et al. also found that drinking decaffeinated coffee had no effect, so you have to go for the real stuff to see these health effects.

The researchers concluded:

In summary, higher coffee consumption was associated with lower risk for all-cause death and death from heart disease, cancer, respiratory disease, stroke, diabetes, and kidney disease. Inverse associations were found in African Americans, Japanese Americans, Latinos, and whites; never-smokers, former smokers, and current smokers; those with preexisting heart disease or cancer; and healthy participants. Our findings support the recent dietary guidelines from the U.S. Department of Agriculture (33), which indicate that moderate coffee consumption can be integrated into a healthy diet and lifestyle, by confirming an inverse association with mortality and suggesting that association’s generalizability to different racial/ethnic groups.

Review of the second study

What I like about this study is that it had a better analysis of major confounders, which gives me more confidence that it’s showing a real decrease in mortality rates for coffee drinkers. Moreover, they have the semblance of a dose response which shows 3-4 cups probably gives you the best reduction in death rate, but I’d like to see much higher consumption, like 10 cups. Maybe there’s a lowered benefit as you drink more, so further research will be informative.

But I have to point out again, the reduction in mortality was, at best, 18%, which may not have any clinical significance.

Coffee health benefits – the summary

These two studies show that there is a strong biological possibility that there is some relationship between lowered mortality and coffee drinking. The European study showed that coffee lowered the risk of dying from liver disease, cancers in women, digestive diseases and circulatory disease.

Moreover, both studies showed that those who drank three or more cups a day had a lower risk for all causes of death than people who did not drink coffee.

Of course, these two studies don’t mean drinking coffee is for everyone. For some people, for example, drinking coffee can lead to serious issues such as cardiac arrhythmias. And of course, excess caffeine can lead to sleep disorders and other issues.

Finally, we don’t know what compound in coffee has this protective effect against mortality. Coffee may contain over 200 different chemicals and compounds, and it might take decades of additional research to identify what chemical (or chemicals) in coffee may provide these health benefits.

I’m going to stand by my point that I previously made. These results are interesting, but they’re not overwhelming. The large numbers in both of these studies to give credibility to the quality of the statistical analyses, but still the risk reduction from drinking coffee seems less than impressive.

I think my skepticism would be reduced if I knew what may be the contributing factor – is it that coffee drinkers are just better people? Or is it some chemical in the coffee? Maybe unhealthy people don’t drink coffee because of a physician’s recommendation, which adds bias to these studies?

So at this time, drink coffee if you like it. It may provide you with some benefit. If you shouldn’t drink coffee, or don’t like it, I don’t think there is enough evidence for you to suddenly change your habits. Coffee health benefits are intriguing, but not quite overwhelming yet.