Taking medications containing caffeine was tied to a doubled or even tripled risk of having a stroke in a new Korean study that might seem to contradict recent evidence suggesting coffee and tea exert protective effects.
But the results may be in fact be in line with that research, according to the study authors, who point out that people who drank the least coffee were most at risk when taking caffeinated drugs.
The products included mostly over the counter pain relievers, cold medicines and alertness aids containing small amounts of caffeine.
"Caffeine is a vasoconstrictor, causing blood vessels to tighten and increasing the pressure of the blood flow," Nam-Kyong Choi of Seoul National University College of Medicine, who co-led the study, said in an email
That effect on blood pressure could explain the possible link to strokes, but the study didn't investigate the mechanism, Choi said.
The researchers selected 940 adult patients who had suffered a hemmorhagic stroke, wherein a blood vessel in the brain bursts and bleeds heavily.
They then compared those patients to a group of similar people who had not suffered a stroke but had been hospitalized, and to a third group who had neither suffered a stroke nor been hospitalized.
The team interviewed all the participants about all medications they had taken in the preceding two weeks.
They found that overall, those who had taken a medication containing caffeine were about two and a half times more likely to suffer a stroke, according to the results published in the journal Stroke.
Five percent of people who had had strokes had taken a caffeine medication, compared to 2.3 percent of the no-stroke groups.
But when the researchers factored in coffee consumption, the participants who took caffeine-containing medications but didn't drink coffee on a daily basis were closer to three times more likely to have strokes than people not taking the medications.
And those who drank plenty of coffee daily did not seem to be at any greater risk.
"Even though caffeine-containing medicines appear to increase the risk of hemorrhagic stroke, it doesn't appear to be the ‘caffeine' dose," said Dr. Daniel Woo, associate professor of Neurology at the University of Cincinnati in Ohio, who was not involved in the study.
"Folks who drank 3 cups of coffee per day didn't seem to have a higher risk of hemorrhagic stroke," said Woo, who is also an associate editor of the Journal for Stroke Research and Treatment.
Since the risk of stroke didn't go up in parallel to caffeine consumption, there was no "dose response relationship" and it's unlikely that caffeine causes strokes, according to Dr. Susanna Larsson, a nutritional epidemiologist who studies caffeine at the National Institute of Environmental Medicine at the Karolinska Institute in Stockholm, Sweden.
"Moderate consumption of coffee (1-3 cups/day), which is the main source of caffeine in most populations, has been associated with lower risk of all types of stroke," Larsson said by email.
One cup of coffee contains about 130 milligrams of caffeine, much higher than the 35 milligrams per day the study subjects got, on average, from caffeine meds.
Total daily caffeine intake from coffee, teas and sodas in the U.S. averages 250 to 300 milligrams daily per person, so an additional 35 milligrams from medications would be unlikely to have any effect, Larsson said.
Choi believes caffeine sources like coffee, tea and chocolate may contain other beneficial compounds that mitigate the effects of caffeine.
The new results might differ from the norm for two important reasons, Woo said: one, there's an inherent bias when doing recall studies with stroke patients, in that the study could only include those patients who still had the mental capacity to consent and answer questions, so the study group didn't represent stroke patients as a whole.
Two, in Korea cold remedies and other medications may still contain phenylpropanolamine, a chemical removed from medications in the U.S. in the early 2000s when a study linked it with an increased risk of stroke.
The patients may have been taking medicines with phenylpropanolamine, or ephedrine, which is common in cold remedies and raises blood pressure, which might have caused the strokes, Woo said.
Choi agreed that medications containing phenylpropanolamine and caffeine deserve extra caution.