Now, however, it's harder to keep track. Companies don't always list caffeine content on food and drink labels. And despite decades of research, no one really knows the lifelong consequences of taking in so much. Studying a drug the majority of people already take is a challenge. Plus, any pro-caff findings might not account for the fact that a huge number of adults are sleep-deprived, says sleep medicine expert Timothy Roehrs, Ph.D., of Henry Ford Hospital in Detroit.
Caffeine has such a big impact on physical performance and endurance that banning it from the Olympics would eliminate most contenders, theorizes John Ivy, Ph.D., an exercise physiologist at the University of Texas at Austin. It can give non-elite exercisers an edge as well, helping them go faster and for longer.
Moderate to heavy coffee intake can also, perhaps, decrease your risk for diabetes, inflammatory diseases, Parkinson's, and dementia. It could improve memory function. And the buzziest current tiding: Coffee drinkers live slightly longer than non-drinkers, per a 2012 study.
Yet for every yea there seems to be a statistical nay. An October 2013 study, for example, concluded that coffee drinkers might have shorter life spans. Caffeine can also disrupt sleep, leading to a long list of problems, including weight gain, weakened immunity, and poor concentration. New research has found that, although tasteless itself, caffeine has an ability to leave people wanting more, driving them toward sugary sodas and energy drinks.
Then there's the issue of addiction and caffeine-use disorder, in which people still guzzle the stuff in the face of known health circumstances (e.g., pregnancy). Studies show that nearly half of all caffeine consumers admit they have problems abstaining, despite occasional overload symptoms such as headaches and insomnia. That's important since, at its extreme, the drug can interfere with your heartbeat; a new report found caffeine-related ER visits spiked 36 percent from 2010 to 2011 alone.
So how much is safe - even helpful? Ideally, you'd use the drug the way you use other meds: only when you need it most, and not in large amounts every day, says Laura Juliano, Ph.D., a psychology professor at American University.
Because caffeine metabolism varies widely in people, it's best to stay as far below that daily limit of 400 milligrams as possible. That's about two 12-ounce cups of coffee, though not all brews are created equal. You'll have to do a little legwork to ID your own caff quotient—if, say, you have a coffee, a bit of chocolate, and a stick of spiked gum, you may be way overstimulated...or not.
Also be mindful of how you indulge. A binge in the a.m. will likely only set the stage for a crash after lunch, which will, in turn, tempt you to seek out even more caffeine, says Roehrs. (Our suggestion: Try waiting until about 10 a.m. for your java jolt.) And it practically goes without saying to skip caffeine within six hours of bedtime.
As with anything else, awareness and moderation are key. Read labels. And if you feel jittery or your caffeine crashes are intense, it's time to cut back.
How the super drug takes you from tired to wired...and back
- Once caffeine hits your bloodstream, it's shuttled straight to the liver, which breaks it into tiny molecules.
- Those then course through your veins, binding to cells, stealing the rightful parking spots of the sleep-inducing chemical adenosine.
- With less adenosine to temper it, your brain is in overdrive. Mentally, you're more alert. Production of feel-good dopamine ramps up.
- Your blood vessels have sprung into action: As they constrict, your heart beats faster, pumping extra oxygen to your organs.
- Your body reaches peak caffeine levels 15 to 45 minutes after ingestion. The effects, however, last much longer. Depending on your genes and what meds you take, you could be wired for the next five to six hours.
- Sounds great, right? Unless you've gone over your personal limit. Excess caffeine can cancel out too much adenosine, over-stimulating your brain.
- Even if you don't go overboard, take note: Brain cells respond to the repeated blocking of adenosine by producing more and more of the stuff, which will hit you harder once your buzz wears off.