Our Scariest Topic Yet

I'm worried today's topic will scare you...

It scares most people... and as a result, they never try to understand it.

I'm talking about science... Just like the talking heads on cable TV and bloggers on the Internet, many people are content to repeat whatever they hear without studying the data and thinking about what the facts mean.

That's not what we do here. We have a team well-versed in medicine and finance that spends days, and even weeks, researching each issue before we write about it for subscribers.

We do this so you don't have to. We know that reading scientific studies is often boring, and the studies are sometimes hard to understand.

Worse, when people misunderstand what they read, or miss key information – like we saw with the World Health Organization's report on bacon – it can breed fear.

Today, we're offering up a quick lesson on scientific studies – like the studies we read concerning the health benefits of coffee. Our recent piece on the health benefits of coffee generated some smart and thoughtful questions... so we thought we'd take a minute and answer a couple in today's letter.

We love to hear reader feedback, even the ones challenging our science. If you have a topic you think we need to cover, send us a line at [email protected].

Q: I'm disappointed in your letter about the benefits of coffee. In almost all cases your data shows only correlation. I'm sure that you know that correlation does not equal causation. Maybe people suffer (fill in the blank) because they sleep poorly and people who sleep poorly tend to avoid coffee. Sleep habits may be the causal factor rather than coffee. This is just one example. – C.T.

A: We're glad someone wrote in about this. This question brings up a point near and dear to us: How can we believe all this stuff about coffee if it's all just correlation and not causation?

Correlation means two measures – like drinking coffee and cancer risk – move in a direction relative to the quantity of the other. In this case, they're inversely correlated – meaning the more coffee you drink (or even just smell), the more your cancer risk decreases. Correlations go the other way, too. Positive correlation means the two measures move in the same direction.

It turns out, most coffee studies are self-reported, meaning the participants have to record what they eat and drink. People often over report healthier behaviors, like saying they exercise three times a week when it's really three times a month. Likewise, they can underreport "bad" behaviors, such as how often they indulge in processed or high trans fat foods.

When we choose studies, we prefer ones with correct statistical analyses and large numbers of participants. The more participants, the stronger the evidence for the correlation. The problem of over/underreporting tends to get averaged out across a big enough population. And significant statistical findings mean that the data reflect more of the real population.

Subscriber C.T. mentions that extra factors may influence the study. These are called "confounders." In C.T.'s example, sleep deprivation may be the real problem causing the health issue, and it just happens these folks drink less coffee, knowing the caffeine will exacerbate their sleeplessness.

Any researcher worth his salt will run the statistical analysis to take confounders into account. That means the findings have to be significant even when things like poor sleep are included.

But C.T. makes a good point: Although strong in their correlation, these studies don't pinpoint the actual cause. That's where thinking about the relationships ahead of time and contemplating what might be the underlying mechanisms of action (MOA) comes in.

MOA studies are usually done in a highly controlled environment, like a laboratory. Let's take a look at one example, using coffee, published in 2011 in the Journal of Nutritional Biochemistry...

Coffee reduces inflammation, a symptom of many diseases, like cancer. Our body naturally fights inflammation with antioxidants. A key protein, nuclear factor erythroid 2-related factor 2 (Nrf2), triggers the release of antioxidants from our cells.

Scientists from the University of Vienna found that several components in coffee directly boost the activity of Nrf2. This means coffee stimulates your body to produce more antioxidants, reducing so-called free radicals. This lowers the ongoing levels of inflammation.

Thus, researchers can describe a plausible mechanism of action for coffee's overall benefits.

This study, paired with several others that show Nrf2's boosted activity is strongest in the liver, helps support point No. 2 ‒ coffee protects you from liver cancer.

So when we report studies, we love uncovering rational MOA studies to support the clinical and relevant correlations. And although my research assistant could probably talk your ears off about things like Nrf2 pathways, we simply don't have the space to do that.

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Q: I read with interest your notes on the benefits of drinking coffee. I agree and like the drink, but in the recent past, it has started giving me an erratic heart rhythm. I started drinking decaf coffee instead, and the heart condition stopped.

However, I want to ask for your opinion on whether decaf coffee still gives the many benefits you attribute to coffee. – A.B.

A: I'm sorry to hear about your trouble with "leaded" coffee. I love being able to get an extra jolt from the stimulant caffeine. But I also love the flavors and benefits without the kick all day long. So I start with caffeine in the morning and move to decaf later in the day.

I don't worry a bit about missing the caffeine because coffee is a rich, complex substance with many beneficial components.

Just as many diseases are multifactorial (cancer, for instance, springs from factors like lifestyle, diet, genetics, and exposure to things like sunlight), so too is coffee multifaceted.

Caffeine is just one of several antioxidants in coffee and the subject of many studies. But it's not the sole reason for all the benefits.

The Vienna study we mentioned earlier found positive boosts to Nrf2 with compounds called chlorogenic acids. Coffee is also a good source of potassium, niacin, and vitamin E – minerals all essential for health and beneficial in their own right.

Several studies show that decaffeinated coffee does have some of the same benefits as regular coffee. For example, in a 2014 study published in Hepatology, both caffeinated and decaf coffee effectively lowered liver enzyme levels (which is great for the health of your liver).

So if you can't have caffeine or don't want the kick-start to your heart... you'll still get benefits from decaf. Even if you don't have a health issue like that, do what I do and enjoy caffeinated coffee in the morning and switch to decaf coffee or tea before 2 p.m. That way the caffeine does its job, but won't keep you up at night.

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