Field of Science

Have another cup o' joe, it's good for you

My favorite science studies are the ones that tell us that what we're already doing is good for us. This story fits the bill. In the American Journal of Epidemiology this month, Janet Hildebrand and colleagues reported on a large study looking at the effects of coffee on throat cancers.

Let's get right to the good news: drinking coffee seems to reduce your risk of death from oral or pharyngeal cancer by about 50%. Drinking more coffee is better than drinking less, and drinking caffeinated (normal) coffee is better than decaf.

I knew there was something wrong with decaf.

Now for some details. This study is part of an enormous project, the Cancer Prevention Study II, with over 1 million participants who've been followed for 30 years. The participants regularly fill out questionnaires answering a variety of questions, including how much coffee and tea they drink. After excluding people with missing information about coffee drinking and those who already had cancer in 1982, the researchers still had over 950,000 people. Coffee drinking was categorized based on daily consumption: less than a cup (or none), 1-2 cups, 3-4 cups, and more than 4 cups. They asked about decaf coffee and tea drinking as well.

A study like this is hard to do well, because there are so many confounding variables, especially smoking. Smokers have a dramatically higher risk of throat cancer, and smokers also drink a lot of coffee. Hildebrand and colleagues did a good job at separating out this effect, looking at the risk of cancer in nonsmokers separately and adjusting the statistics accordingly.

Perhaps the most encouraging finding is this: in people who have been nonsmokers for at least 20 years, 1-2 cups of coffee per day corresponds to a 32% decrease in the risk of death from throat cancer.  More than 2 cups per day corresponds to a 64% decrease. And among all participants (including former smokers), more than 4 cups a day seemed to provide the greatest benefit.

Decaf coffee also seems to reduce the risk of fatal throat cancer, though not quite as much. Tea drinkers, in contrast, don't seem to get any benefit, not for this type of cancer.

All this comes with some very big caveats.  First, despite the very large size of the study, the number of deaths oral or pharyngeal cancer was very small, only a few hundred. (Oral/pharyngeal cancer is very common worldwide, but less common in the U.S., where this study was conducted, with about 7850 deaths per year. This includes cancers of the tongue, mouth, and pharynx.)  So the absolute risk is very small.  Another big caveat is that this study only looked at cancer deaths - it did not measure the risk of getting cancer in the first place.

But skepticism aside, drinking coffee seems to reduce the risk of oral cancer.  This confirms my long-held view that the three major food groups - coffee, chocolate, and red wine - are all good for you.  So the next time you feel like a second cup, or a third: drink up!

3 comments:

  1. The thing that irritates me about coffee studies is that they always refer to “cups” of coffee, never defining how much coffee (caffeine) is in the non-defined “cup”. A standard “cup” (if you go by the markings on your coffeemaker pot) is 6 oz. I make a 16 oz coffee every morning--just for starters. My Mom puts about 2 teaspoons of grounds in her basket for 8 cups of brewed coffee, of which she drinks a couple of small mugs, probably about 8 oz.. I put four large scoops (approx 2 Tbsp ea) in my drip filter cone for the 16 oz cup. I often have another, although it will probably be decaf or half-caf. I will also have a 12 or 16 oz latte with 2 or 3 shots of espresso if I go somewhere that’s near my favorite coffee bar. Is a latte a “cup” of coffee?

    We both report drinking two cups of coffee per day. How is this helpful as to determining how much caffeine helps prevent cancer?

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  2. Yes, that is annoying - but this study was quite precise, specifying a cup as 237 ml. I measured my standard mug o' coffee, and that was pretty close to a full mug. 237 ml is 8 ounces, by the way - so this study used a more normal definition of "cup". They didn't say how strong the coffee was, and even if they did, this was a survey-based study, not a controlled trial, so the numbers are all approximate anyway.

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  3. And maybe that could be what the effect is? What we're seeing here could be the placebo / de-stressing effect from each cup of coffee enjoyed by the drinkers regardless of how strong each cup is?

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