"Do the Health Benefits of Coffee Apply to Everyone?"
Three-quarters of American adults drink coffee,
about half of which on a daily basis.
That comes out to a million tons of coffee every year.
Might there be "grounds" for concern?
Population studies have found that coffee drinkers tend to have
lower risk of Parkinson's, less prostate cancer (especially the women),
less liver cancer, less diabetes, liver cirrhosis, depression among women,
and a reduction in mortality overall, such that coffee drinkers tend to live longer
than non-coffee drinkers, with mortality bottoming out at about four cups a day.
But these are all just associations.
You don't know if it's cause and effect until you put it to the test.
For example, coffee really does seem to protect the liver.
Take people with chronic hepatitis and have them drink coffee, or not,
for a month, then switch them back.
And the coffee really did seem to help.
Similarly, randomize Parkinson's patients to get two cups of coffee's worth
of caffeine and get a significant improvement
in movement symptoms within three weeks.
Runners, randomized to drink coffee, shaved about six seconds off their mile.
Weight lifters, randomized to coffee, can squat more weight,
about 600 pounds more worth of reps.
And not just athletic performance.
A cup of coffee's worth of caffeine can significantly improve IELT,
which stands for "intravaginal ejaculation latency time,"
from two minutes all the way up to five.
Unfortunately, those effectively randomized at birth to genetically
just have a higher predilection to drink coffee
do not appear to be protected from diabetes, or depression,
or Alzheimer's, or obesity, or metabolic syndrome.
So it seems the protective associations may just be due to confounding factors,
like maybe those who drink coffee just happen to exercise more or something.
And the same with prostate cancer: no apparent cause-and-effect relationship,
and even the mortality benefit seemed to disappear.
Even if a study did show coffee drinking could
extend lifespan by reducing inflammation or improving
lung function, or insulin sensitivity, that would mean on average.
There is "inter-individual variability" after consumption
of major plant-food compounds, meaning people may respond differently.
For example, how crazy is this: in some rare individuals, heavy use of caffeine
apparently provokes sleepiness.
That's an extreme example.
Most of the time it's just that some individuals may benefit more than others
from the health effects of different foods.
For example, because of differences in gut bacteria, only a minority of Westerners
may derive extra benefit from soy, as I've described before.
The most common difference in caffeine effects is that, while most people
metabolize caffeine rapidly, certain gene variants in liver detox enzymes
make some people slow metabolizers.
Might that make a difference?
Well, habitual coffee consumption of at least three cups a day
has been associated with uncontrolled blood pressure among older individuals
diagnosed with hypertension, suggesting that moderating
coffee intake may be a good idea for some people.
But even if it was cause-and-effect, that would be on average.
What would happen if you split people up by how fast they metabolize caffeine?
Compared to coffee abstainers, those who have impaired caffeine metabolism genes
have an elevated risk of becoming hypertensive at one to three cups a day,
and especially at four or more.
OK, but check this out.
For the rapid metabolizers not only was there no excess risk
at one to three cups, heavy coffee drinkers were protected,
meaning apparently the more coffee they drank,
the lower their risk. How do we explain that?
Coffee is a complex blend of a vast number of different compounds.
There are protective polyphenol antioxidants that are beneficial.
Coffee beans are, after all, beans—
well, actually, seeds, but seeds are really healthy too.
On the other hand, there's the caffeine, which can spike adrenaline levels
in the blood, but only if you're a slow metabolizer.
Rapid metabolizers can clear caffeine so fast
that there's no increase in adrenaline even at four or more cups a day.
And so then you just have the beneficial polyphenols that actually
lower your blood pressure, hence the benefit overall.
Thus, there seems to be a Jekyll and Hyde aspect to coffee
whose overall action on the cardiovascular system appears
to be regulated by that gene for the enzyme
that metabolizes caffeine.
The important question, though, is does it give women larger breasts?
W-h-a-t?
Young women who drink a lot of coffee and are rapid caffeine metabolizers
have about a half-a-baseball-sized larger breast volume, which may be
a bad thing as breast volume is associated with breast cancer risk.
But no, the important question is what about heart attack risk?
In slow metabolizers, daily coffee consumption appeared to double
the odds of a heart attack, or even quadruple the odds at four cups a day,
whereas in the rapid caffeine metabolizers, daily coffee consumption
was protective, cutting the odds of a heart attack by more than half,
or at least until you get up to four or more cups a day.
The protective effects observed among rapid metabolizers suggest
that the efficient elimination of caffeine might have unmasked
the protective effects of other phytochemicals in coffee.
We think it may be the adrenaline again,
since if you're a slow metabolizer of adrenaline, high coffee consumption
may put you at risk as well.
So, is coffee friend or foe?
These studies suggest the possibility that slow caffeine metabolizers
who consume caffeinated coffee may have an increased risk
of cardiovascular disease,
whereas fast caffeine metabolizers may be protected from this risk
by the antioxidants and other beneficial compounds present.