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This article originally appeared in
the October 2005 Harvard Men’s
Health Watch and is provided courtesy Harvard
Health Publications.
Coffee and your blood pressure
Coffee has been part of the human diet for about 1,000
years. During much of that time, it has stimulated controversy — and
in the age of Starbucks, the dispute has blossomed from a tempest in a coffee
pot to grounds for serious debate. Some of coffee’s negative press
seems to depend on the widespread belief that anything that tastes so good
must be bad for you. But there is a serious side to the argument: Coffee
stimulates the nervous system, increasing alertness but interfering with
sleep. Acting as a diuretic, it stimulates the flow of urine. And it stimulates
the cardiovascular system, boosting the heart rate and raising blood pressure.
But the circulatory effects of coffee are more complex than they seem, and
an interesting study can help you filter out fact from fiction.
A fresh look
Most doctors advise people to avoid coffee (and other sources of caffeine)
before they have their blood pressures checked. It’s standard advice
based on the notion that caffeine raises the blood pressure enough to interfere
with an accurate measurement. But medical research has been murky; some
studies support a link between coffee drinking and hypertension, but others
do not — and a 1987 Italian investigation suggests that coffee may
even help to reduce blood pressure.
After poring over these divergent views, scientists from Switzerland
and the United States decided to take a fresh look by performing detailed
studies on 15 volunteers. None of the subjects had high blood pressure or
hypertensive parents, and all were healthy nonsmokers; only six were habitual
coffee drinkers.
The researchers monitored each volunteer’s blood pressure, heart rate,
and sympathetic nervous system under four conditions: before and after drinking
a triple espresso, before and after drinking a decaffeinated triple espresso,
before and after receiving 250 mg of caffeine by intravenous injection,
and before and after an intravenous placebo (salt solution).
A triple espresso causes quite a jolt, and it did jolt blood pressure
readings. But although blood caffeine levels rose to a similar degree in
all the subjects, not all experienced a rise in blood pressure. In fact,
espresso did not boost the pressures of habitual coffee drinkers, though
it raised systolic pressure readings on average by 13 mm Hg and diastolic
pressures by 7 mm Hg in subjects who were not coffee drinkers.
Espresso is strong stuff, but an intravenous slug of caffeine should
be even more potent. Indeed, blood caffeine levels rose to the same degree
after the caffeine injections and the espresso. But the straight-up caffeine
had a much smaller effect on blood pressure than the espresso, boosting
systolic blood pressure by an average of just 6 mm Hg. Moreover, the coffee
drinkers and the nondrinkers responded similarly to intravenous caffeine.
A simple cup of coffee contains hundreds of complex substances. Caffeine
gets the blame for raising blood pressure, but the disparity between espresso
and pure caffeine suggests there is more to the story. The decaffeinated
espresso proved the point. It did not raise blood caffeine levels, but it
boosted the average systolic blood pressure of the nondrinkers by 12 mm
Hg, virtually as much as the high-test brew.
Coffee and your blood pressure
The study helps explain why earlier investigations produced such variable
results. Coffee does raise blood pressure in people who are not used to
it but not in regular coffee drinkers; youngsters appear more sensitive
to coffee. And the hypertensive effects of coffee seem to depend on ingredients
other than caffeine. Habitual coffee drinkers become acclimated to these
ingredients so their pressures don’t rise more than a point or two,
but people who are not used to coffee can expect a temporary rise in their
pressures after drinking regular or decaf.
Coffee and your health
Blood pressure is an important predictor of heart attack and stroke.
Even if coffee doesn’t raise blood pressure in regular drinkers, does
it live up to its reputation as a cause of heart disease? In a two-year
study of 45,589 men between the ages of 40 and 75, Harvard scientists found
no link between coffee consumption and the risk of coronary artery disease
or stroke, even in heavy drinkers. But while regular coffee proved harmless,
decaf was associated with a slightly increased risk of heart disease, though
the link was weak. The Scottish Heart Health Study was even more reassuring,
reporting a reduced risk of heart disease in coffee drinkers, with heavy
drinkers getting the most benefit. And although some coffee drinkers are
annoyed by a feeling of rapid pulse, coffee does not seem to cause serious
disorders of the heart’s rhythm, even in recent heart attack patients.
Coffee is a complex brew, and it has many effects beyond the cardiovascular
system. Some people benefit from increased alertness, but for others the
neurological actions of coffee include insomnia, anxiety, or tremors. Habitual
coffee drinkers develop a mild dependence, so sudden withdrawal can trigger
temporary headaches or depression. Migraine sufferers may have an attack
triggered by a sudden increase or decrease in coffee consumption.
Some coffee drinkers benefit from an increase in bowel motility, which
relieves constipation, but others develop gastroesophageal reflux and heartburn.
The Harvard studies suggest that coffee drinkers enjoy a reduced risk of
diabetes, gallstones, and kidney stones, and an Italian study hints at some
protection from colon cancer. Coffee does stimulate urine flow, which can
be a trial for men with benign prostatic hyperplasia, but contrary to common
beliefs, it does not cause dehydration.
Coffee’s effects on the metabolism are just beginning to be evaluated.
It does seem to elevate homocysteine levels, which could increase the risk
of heart attack and stroke, but coffee drinkers don’t seem to suffer
these consequences. Boiled, plunger pot, Turkish, and espresso coffee can
raise blood cholesterol levels, but filtered, perked, and instant coffee
do not. Coffee widens the bronchial tubes, providing mild benefit for some
asthmatics.
It’s a complex equation, but it all boils down to this: When it comes
to coffee, the choice is yours. If you enjoy coffee, drink it to your heart’s
content. But if it bothers you, reduce your consumption or give it up.
Until the last drop of scientific data is in, common sense and moderation
are the best guidelines. And whether or not you choose to drink coffee,
don’t let the question brew up arguments that really might raise your
blood pressure.
© 2006 Harvard Medical International. ALL RIGHTS
RESERVED.
Links to external sites should not be construed as endorsement by HMI or Harvard
University.
NEWSLETTER STAFF
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Chris Railey | Editorial Assistant: Amanda Wong, Mike Pastore | Production
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