A fresh look

I just got a new coffee machine, and I love it! But, should I be using it? 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.

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.

Do you drink coffee? Have you ever talked with your doctor about its effects on your blood pressure?

Julie K. Silver, M.D.,is an assistant professor in the Department of Physical Medicine and Rehabilitation at Harvard Medical School. She is also the Chief Editorof Books for Harvard Health Publications.

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