If you live in a college town, you might have noticed that campus coffee shops are still buzzing late into the evening.
And that makes sense. New survey data from the NPD group, which tracks trends in what Americans eat and drink, finds that 18- to 24-year-olds are turning to coffee, rather than caffeinated sodas, as their pick-me-up of choice.
In 2002, about 25 percent of 18- to 24-year-olds reported drinking coffee sometime within a two-week period. But by 2012, the percentage of young adults drinking coffee in that same time frame hit 39 percent.
"It's an explosive growth in the consumption of coffee," says Harry Balzer of the NPD Group.
For evidence of this trend, I hit a coffee shop near the campus of George Washington University, which is just a Metro-ride away from NPR headquarters here in D.C. In midafternoon, I found a packed house.
"This is nothing for two o'clock in the afternoon," senior Arturo Lichaucho tells me. Often times, the line is out the door and around the block, he explained, and lots of students hit the coffee shop before hitting the books in the late afternoon.
The students I chatted with gave lots of reasons for a steady coffee habit, including increasing demands on their time that lead to less sleep, and the 24/7 culture of overstimulation. And why not drink more coffee?
Recent studies link coffee consumption to a range of good health effects, including decreased risk of dementia and decreased risk of depression among women.
But experts say there is one downside that's often overlooked: Coffee consumption can get in the way of a good night's sleep.
"Our data has shown that a brewed coffee contains much more caffeine than a cold cola beverage" says Bruce Goldberger, a toxicologist at the University of Florida.
The Center for Science in the Public Interest took a look at several popular items and analyzed their caffeine content. It found that a 12-ounce cup of coffee from Starbucks contains about 260 milligrams of caffeine, which is about five times more than a 12-ounce can of Diet Coke.
The caffeine content of coffee varies widely. McDonald's coffee, for instance, has about 100 mg for a similar-size serving, which is significantly less than Starbucks. And Dunkin' Donuts coffee is somewhere in the middle. For more comparisons, see their caffeine content chart.
When adolescents and young adults are habituating to the effects of caffeine, it's easy for them to overdo it. And often, even adults with lots of experience drinking coffee don't necessarily connect sleep problems to caffeine consumption.
"There are absolutely negative implications," explains Amy Wolfson of the College of the Holy Cross in Massachusetts, who has studied how caffeine influences sleep among adolescents.
For instance, studies have linked high caffeine use to decreased REM sleep.
"We know that REM sleep is needed and has positive implications for memory consolidation and learning," says Wolfson. And if college students are getting too little sleep, or poorer quality sleep, Wolfson says, it's likely to have negative implications for academic performance.
So what's the smartest way to consume coffee for the boost but without the bust of a good night's sleep?
Pay attention to how much you drink, and when you drink it.
Consider this: The half-life of caffeine in the body can range from 2 1/2 hours to 12 hours. Because of genetic differences, some of us metabolize caffeine much more quickly than others.
But Goldberger says the typical half-life is probably about five hours, which means caffeine typically stays in the body for about 10 hours — or longer. (Technically, he says it takes up to five half-lives to rid the body completely of a drug.)
"If someone has a cup of coffee at 7 p.m., the caffeine that they've ingested is still in the body affecting the central nervous system when they're going to bed," says Goldberger.
So as a rule of thumb, if you want to go to sleep by midnight — and stay asleep — it's probably best not to drink coffee after 2 p.m.
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