Coffee is such a powerful stimulant, even the smell of it can wake you up.
Most of the world drinks coffee, or consumes caffeine
in other forms like tea, cocoa, or mate.
It's the world's most consumed mind-altering drug.
So, is it dangerous?
People have been asking this for hundreds of years.
In the 1700s, Sweden's King Gustav III made a prisoner drink three pots
of coffee a day to see how fast it would kill him.
The prisoner's twin had to drink the same amount of tea.
The tea-drinker died first, though both outlived the guys running the experiment,
and also King Gustav himself, who was assassinated in 1792.
More recent studies have been a bit more scientific.
And some of them scared a lot of people off coffee.
In the 1970s, scientists gave coffee to lab rats.
And found some of them gave birth to babies with missing toes.
Around the same time, a study on humans found a strong correlation
between coffee consumption and bladder cancer.
But the studies were seriously flawed.
The rats were given ridiculously large amounts of coffee, like 12-24 cups a day.
And the people with bladder cancer?
It was later proven that drinking lots of coffee wasn't giving them cancer.
It was because they had cancer, and were often peeing more,
that they drank more fluids—including coffee.
These days, most people worried about caffeine talk about addiction.
And recently, scientists have been trying to figure out
exactly how the drug works in the brain.
We all know caffeine makes you more alert.
But when caffeine blocks the chemicals that make you drowsy,
it makes other changes in your brain as well.
In particular, it makes the brain more sensitive to dopamine,
the feel-good chemical that makes drugs like cocaine and heroin so addictive.
But there's one major difference between an "addiction" to caffeine and hard drugs.
Cocaine is addictive because it activates of the brain's reward system,
which doesn't just makes us feel good,
it has us seek out that good feeling over and over again.
Caffeine doesn't do that.
Which is why cutting your coffee intake will probably leave you
with nothing worse than a headache.
So it's not an actual addiction.
But that still raises an important question for scientists:
Here's Dr. Astrid Nehlig, who's been researching coffee and caffeine for 30 years.
She says even though caffeine isn't addictive,
there are lots of reasons it might feel that way.
But caffeine does stimulate the brain, so it is technically a drug.
And it doesn't take that much to kill you: about 10 grams.
That works out to about 100 cups of coffee, consumed within several hours.
Since it takes 25 cups of water to kill you,
you'd die of water intoxication long before the caffeine could do anything.
Generally, up to 400mg of caffeine a day is considered safe.
That's four cups of coffee.
But here's the thing.
No one can really tell you how much you should drink,
because everyone is genetically wired to handle caffeine differently.
Here's Dr. Marilyn Cornelis at Northwestern University,
who's studying how our bodies break down caffeine.
That means, our bodies know when enough caffeine is enough.
And there's plenty of new science showing coffee
does more than help you concentrate.
Lifelong coffee drinkers are less likely to suffer
from Alzheimer's and Parkinson's diseases.
Which all suggests that coffee isn't something to worry about.
In fact, it's probably already doing you a lot of good.