Credit: Flickr user Ben Cumming
Caffeine was my drug of choice in high school. I didn’t smoke cigarettes, go to beer bashes, use illicit drugs, or abuse prescription medication. Instead, my friends and I hung out past midnight at a local diner, downing cup after cup of heavily creamed-and-sugared coffee. Free refills and attractive waitresses kept us coming back night after night. We left $2 tips for our $1.50 tabs. Somehow, amazingly, we managed to get to sleep every night and off to school every morning.
By the time I reached college, coffee had become more of a study aid than a social lubricant. Now, more than 20 years later, I still haven’t shaken the habit. I can’t imagine writing this column without a hot cup of coffee (although for the past decade I’ve limited myself to “half-caf” — an accommodation to an aging stomach).
But does that caffeine really help me do my job better? Or am I just feeding an addiction? There is no question that caffeine has addictive properties. Consuming as little as a cup a day of coffee can make you dependent on coffee, which means when you stop drinking it, you’ll experience withdrawal symptoms like headaches, irritability, and drowsiness. In other words, you’ll be just like me, before my first cup of coffee in the morning.
The study I linked above found that caffeine withdrawal occurs in people who consume as little as 100 milligrams of caffeine per day. But how much is that? As nutrition blogger Colby Vorland pointed out last month, that’s not an easy question. Vorland cites two studies that attempted to measure the caffeine content of coffee. The researchers found that depending on where you get your coffee and how it’s prepared, the caffeine content in a serving can vary from 58 mg to 259 mg. Espresso shots in general had less caffeine than brewed coffee, ranging from 58 to 92 mg per shot; the 259 mg of caffeine was in a 16-ounce cup of Starbucks brewed coffee.
In a separate study, researchers measured caffeine content of “identical” cups of brewed coffee purchased on separate days, and found striking variance: 475 milliliters (16 ounces) of Starbucks Breakfast Blend contained as little as 259 mg and as much as 564 mg of caffeine. In another study, even decaf espresso was found to contain between 13 and 16 mg of caffeine. That means the half-caf Americano I order from Starbucks actually has about 73 milligrams of caffeine, or more than I’d get in a typical 235 ml (8 ounce) cup of “fully caffeinated” Dunkin’ Donuts coffee.
Caffeinated colas also have significant variance in caffeine levels based on brand, although the individual servings don’t vary as much. A 355 ml (12 ounce) Coke has about 35 mg of caffeine, while a Mountain Dew has around 54 mg. So to support a caffeine addiction with 100 mg of caffeine, you might consume as little as one-fifth of a cup of coffee, or as much as three cans of Coke a day.
Still, the initial question remains: Does that caffeine really do anything for you? Here too, the results are varied. Vorland cites a study published in this month’s Neuropsychopharmacology. The researchers deprived 379 people of coffee for 16 hours, then asked them to rate their levels of alertness. Then they gradually give them caffeine. It took habitual coffee drinkers 250 mg of caffeine before they reported alertness levels equal to non-coffee drinkers—so the caffeine only seems to serve to remove withdrawal symptoms. But even in non-coffee-drinkers, the caffeine they consumed didn’t improve alertness. Caffeine doesn’t seem to work for anyone.
But this study is problematic in that it relies on self-reported results. Two years ago, in one of my all-time favorite blog posts, developmental psychology graduate student Chris Chatham instructed readers on how to get “optimally wired” on caffeine. He pointed to a 2004 study showing that small doses of caffeine, 20 to 200 mg per hour, administered in a laboratory setting, really do help people stay awake.
And last year, the neuroscientist who blogs as “Neuroskeptic” wrote about another study, where researchers administered either decaf or regular coffee to coffee lovers, then had them do a difficult computer task. Those drinking regular coffee did significantly better on the task. Interestingly, if they were told that coffee typically helped on the task, then the volunteers actually did worse after drinking decaf coffee, while performance improved after drinking regular coffee! Still, in this study, since everyone was a coffee drinker, the reason caffeine improved performance could have been removal of withdrawal symptoms, not any real benefit of caffeine.
So if coffee works at all to improve alertness, the 2004 study mentioned by Chatham offers the best advice: If you’re trying to stay alert on a long road trip, regardless of whether you’ve got a styrofoam cup of watered-down joe from a gas station or a double-walled thermos filled with Starbucks rocket fuel, you should sip slowly rather than chug the whole thing!
Dave Munger is editor of ResearchBlogging.org, where you can find thousands of blog posts on this and myriad other topics. Each week, he writes about recent posts on peer-reviewed research from across the blogosphere. See previous Research Blogging columns »
Originally published August 4, 2010