Caffeine ups blood pressure in hard-core users too
March  31, 2004

(Reuters Health) - Even people who would never start the day without their coffee fix may not become tolerant to the blood pressure-raising effects of caffeine, new research suggests.

Although it's still unclear how important caffeine is in contributing to high blood pressure, the new findings suggest that people at risk of hypertension may want to reconsider that second cup of java, researchers say.

The study of 97 adults who regularly consumed caffeine found that half showed small spikes in blood pressure shortly after taking caffeine capsules, even after spending the previous five days downing the equivalent of six cups of coffee per day.

The findings counter the idea that regular caffeine users develop complete tolerance to the stimulant's blood pressure effects, according to researchers.

Dr. William R. Lovallo, with the VA Medical Center and the University of Oklahoma Health Sciences Center in Oklahoma City, and his colleagues report the findings in the journal Hypertension.

Many laboratory studies have shown that caffeine causes a short-term rise in blood pressure, but population studies have failed to definitively link caffeine intake to a higher risk of hypertension. One of the proposed explanations is that in real life, caffeine fiends develop a tolerance to its blood pressure effects.

To test that idea, Lovallo and his colleagues had healthy adult volunteers go through a four-week trial that measured their blood pressure responses to a caffeine "challenge" -- two separate doses of caffeine, given four hours apart, that were each equivalent to two to three cups of coffee.

During one of the study weeks, participants were given placebo pills, which did not contain caffeine, for five days before the challenge tests. On another week, they took pills containing 300 milligrams of caffeine -- about three coffee cups' worth -- each day before challenge testing; and on a third week, they took daily doses of 600 milligrams of caffeine.

The idea was that, if regular users become tolerant to caffeine, participants would show much smaller blood pressure responses to the challenge tests during the caffeine weeks than during the placebo week.

The researchers found, however, that while half of participants were "completely tolerant" to caffeine after taking caffeine capsules for five days, the other half continued to show a blood pressure response. All were regular consumers of caffeine before the study, taking in the equivalent of four to five cups of coffee a day.

The blood pressure responses were small, a matter of a few points on a blood pressure reading. And for most people, according to Lovallo, the minor blood pressure change that may come with a morning coffee is likely harmless.

"For most people, it's probably fine to consume moderate amounts of caffeine," he told Reuters Health.

Where things get more complicated is with people who have a family history of hypertension or have borderline "pre-hypertensive" blood pressure. There's evidence caffeine has a greater blood pressure effect in these individuals, Lovallo said, and they might want to limit their intake.

Dr. Martin G. Myers of the University of Toronto in Ontario, Canada, agreed that moderation is in order when it comes to caffeine.

There is "little evidence," he writes in an accompanying editorial, that drinking two to four cups of coffee a day causes a blood pressure increase of "any clinical importance." He advises that people with or at risk of high blood pressure not consume any more caffeine than that.

"At the moment," Myers writes, "it would seem premature to add moderate caffeine consumption to our list of 'perils of daily living'."

SOURCE: Hypertension, April 1, 2004.