Recently I had coffee with a friend where we discussed the theatre and expense of ordering a coffee from a barista. My friend is a tea drinker and felt indignant about paying the same amount for a tea bag and hot water as those that get the “banging of the group head, drama and construction of the pagan symbols in the foam.” As a drinker of LBs I certainly agree with this sentiment and not surprisingly, this brought up a discussion on the REAL COST of a cuppa. The ramifications... The long term price tag.
In EBM we often refer to a tipping point – the dose of the drug that cures vs. the amount which kills; the collective benefit before the downfall. The discussion of caffeine is not limited to coffee (energy drinks are also included) and the cumulative effects are often overlooked.
Concerns have been raised that too much caffeine could be bad for you; if you are given a massive acute dose of caffeine, you raise your pulse and BP, get the shakes, dehydrate and high doses can be fatal. But what is a high dose? Is there a tipping point? A recent study from The Mayo Clinic has shown that heavy coffee consumption is linked with all cause mortality. Researchers report that heavy coffee consumption, defined as more than 28 cups of coffee per week cause mortality is more pronounced. Previous studies had suggested an association between heavy coffee consumption and all-cause mortality and coronary heart disease, but many of these older studies are compromised, because heavy coffee drinkers were also smokers, two habits that went hand in hand. When adjusted for smoking, the coffee did not appear to be toxic. There are some potential benefits of coffee, although these data points are not particularly strong (and no, reduction in morning-cranky-ness does not count as a clinical endpoint). If you look for the studies you can find good ones (i.e. PROBE CT) that suggest coffee might protect against heart failure, diabetes, stroke, and other medical conditions. People who report intakes of low amounts of coffee are not getting significant harm, and that's up to about 28 cups a week – which is a decent amount of caffeine. One of the researchers did stress that “a cup of coffee as measured is an 8-oz cup, and not the supersized 20-ounce cups typical of Starbucks and other coffee chains.”
Why would a high amount of caffeine increase non-cardiovascular mortality, particularly in young people? The mechanism is not clear. It might be only an association. It may not be that coffee caused the death. This is the case with studies that aren't randomized, and we're never going to get a randomized study of something like coffee. But a good rule of thumb is 4 cups (or less) in a day. There's something to the first or second cup, but if you're drinking it all day long it's really just a habit. And if you have a signal for increased mortality, it might just make people think or stop after their third cup.