For the average adult, 200 to 300 milligrams of caffeine is safe, according to the Mayo Clinic. That's about three 8 oz. cups of coffee or one and a half 12 oz. energy drinks. (CHRIS MADDALONI / STAFF)
It is, quite simply, the national drug of choice. And if you're like most Americans, you've already gotten your fix today. Probably a few times. Brew it, pop it, chew it, eat it, chug it whatever your preferred delivery vehicle, caffeine will give you the heart-pumping, mind-bending buzz so many of us have come to crave.
In fact, more than any other drug, the military makes it oh-so-easy to score your next hit.
While cigarettes and booze have long since disappeared from field rations, caffeine is the one vice Uncle Sam still supplies to the troops.
From chow halls to MREs, from ships at sea to the most remote forward operating base, you can guarantee caffeine is there. And anyone who's done a tour downrange knows it's not just in the ubiquitous cup of coffee anymore.
There's no denying caffeine will keep you going with increasing levels of alertness. In one study, 68 SEAL trainees were given 100- to 300-milligram doses of caffeine after 72 hours of sleep deprivation and then tested. Higher doses "significantly improved visual vigilance, choice reaction time, repeated acquisition, self-reported fatigue and sleepiness with the greatest effects on tests of vigilance, reaction time, ... and alertness," according to the results.
But, while caffeine juices up vigilance and your ability to stay awake, it does not necessarily have the same impact on higher thinking. In studies conducted at the Walter Reed Army Institute of Research, Maj. William Killgore found "you may be able to make decisions quickly, [but] they just might not be good decisions. ... Caffeine will wake you up, but you'll still be making decisions like you're drunk."
Doses of about 300 mg and under have been shown to improve overall mood and happiness. However, for those suffering from increased levels of anxiety, particularly post-traumatic stress, caffeine can be problematic.
"No question about it," says Dr. Barry Smith, a research psychologist at the University of Maryland. "Caffeine will increase levels of anxiety, especially among those already prone to anxiety. It won't cause PTSD, but it will make it worse."
A safe amount
Caffeine-laced gum is standard issue now, while caffeine-spiked sports drinks and even water are commonplace. It's in the off-duty mix, as well, showing up in everything from beer to Red Bull cocktails and high-octane 2-ounce shooters on the side.
But is it safe? For every study proclaiming its perks, it seems there's another warning of its wickedness.
Still, there are some basics that most agree on.
For the average adult, 200 to 300 milligrams of caffeine a day is safe, according to the Mayo Clinic. That's about what you'd find in two to four cups of brewed coffee.
But "average" can be hard to pin down. Weight, age, sex, genetics and pre-existing conditions all play a role in how caffeine affects people.
Most experts also agree that caffeine can unleash a blistering barrage of side effects, especially as doses increase or as withdrawal sets in for those hooked on the drug. Symptoms include insomnia, nervousness, restlessness, irritability, nausea or other gastrointestinal problems, fast or irregular heartbeat, muscle tremors, anxiety, dehydration, and, of course, the dreaded headaches.
But don't get too worked up.
"Up to five cups of coffee a day or about 500 milligrams and for some even more, is going to be perfectly fine," says Smith, a caffeine expert and director of the human-psychophysiology lab at the University of Maryland.
Like a pot of the black stuff on the tossing mess desk of a Navy warship, conventional wisdom has ebbed and flowed over the years on the merits of caffeine, Smith says.
"There have literally been thousands of studies done, and the drug has certainly had its ups and downs in terms of whether or not it's thought to be helpful," he says, "but the current research over the past 10 years suggests that there are no obvious lasting dangers and that, in fact, there may actually be some benefits."
However, he cautions that some people are more sensitive to caffeine than others. "If you get the shakes after one or two cups of coffee, you probably shouldn't drink it, but even then you're not necessarily in any real danger."
Still, about 35 people have been killed by caffeine poisoning over a 21-year period, says Bill Aaronson, a spokesman for the Seattle-based Caffeine Awareness Association.
"That's mostly from pills and energy drinks," Aaronson explains, because of their higher caffeine concentrations. Coffee moves through the body too quickly to be deadly, he says. It would take more than 50 cups of coffee to create a lethal dose.
To put the statistics in perspective, you have a far greater chance of getting hit by lightning 28 people were killed in strikes last year alone than dying from a caffeine overdose.
Killgore prefers the middle ground.
"Caffeine has got good things and it's got bad things," he says. "Like anything else, you just need to be wise in how you use it."
Caffeine's main benefit for those in the military is its ability to keep the internal lights on when the body wants to sleep.
"When sleep is not an option, caffeine is probably your best alternative," Killgore says. Studies have shown that troops can perform for up to 98 hours with 200-mg doses every two hours. "It will help keep you more vigilant and alert, but it doesn't replace sleep. It's just a temporary crutch you have to go back and make it up."
Caffeine can wreak havoc on sleep cycles, making it harder both to fall asleep and to stay that way once you're down. Its half-life the time it takes for half of its impact to wear off is about five hours, and then it takes another three hours for the rest of it to leave your system.
Try this trick the next time you're running on empty but only have time for a quick catnap: Grab a dose of caffeine before you grab the Z's. If you drink your caffeine, it will take about half an hour before it kicks in, pulling you out of your nap nosedive before you hit the fog-inducing deep sleep. "The combined effect is even more powerful than either the nap or the caffeine alone," Killgore said.
It's impossible to say how much caffeine is entering the military's bloodstream every day, but it's certainly a huge part of the national diet.
The use of energy drinks alone has been exploding in recent years, says John Sicher, editor of Beverage Digest. "We've seen yearly double-digit growth," he said.
In 2006, energy drinks pulled in $4.9 billion; by 2008, it was up to $6.5 billion.
Caffeinated drinks bookend the top-five list for liquid consumption in America, he said. Carbonated soft drinks, "which are by far mostly caffeinated," Sicher said, top the list, followed by beer, bottled water, milk and coffee.
Coffee, he said, represents about 9 percent of the 182.5 gallons of fluid experts estimate each adult drinks every year. Soft drinks account for 29 percent.
Officials with the Army and Air Force Exchange Services say the military's cut of the high-voltage power-drink market has seen even bigger growth. In 2006, sales were about $26.6 million. By 2008, PX registers rang in $69 million for energy drinks, AAFES spokesman Judd Anstey said. And that doesn't include even more sales from base commissaries and outside-the-wire purchases.
Of the top 10 highest-selling beverages sold by AAFES, Nos. 1 through 8 all contain caffeine. The top seller? The Monster Energy drink.