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Coffee Slows Blood Flow to Brain

Study shows it can confound results of medical research

FRIDAY, Dec. 7, 2001 (HealthDayNews) --Your morning jolt of java may slow blood flow to your brain.

But don't worry. A new study shows the effect is temporary and your brain adjusts over time.

However, the research suggests that scientists need to watch how much coffee their subjects consume because it can affect the outcome of various tests.

Dr. Aaron Field, a University of Wisconsin researcher, wanted to see if caffeine would affect the results of functional magnetic resonance imaging (fMRI) tests. These measure blood flow in the brain, and show doctors which brain areas are used to perform specific tasks. Currently, the scans most often are used for research purposes.

Field and his colleagues recruited 11 healthy adults for his study. Six usually drank less than one cup of coffee a day, and five averaged several cups of coffee daily. All were asked to abstain from caffeine for 30 hours before the testing.

Each group was given two tests -- one with a placebo pill and one with a pill that equaled the caffeine in two to three cups of coffee.

"Cerebral blood flow went down in everybody when they got caffeine; on average, about 20 percent," says Field. Interestingly, all heavy caffeine users had more blood flowing to their brains to begin with, he says.

"The brain seems to have adapted to high caffeine levels and changed its [blood flow] set point," he says.

Field presented his findings recently to the Radiological Society of North America Scientific Assembly and Annual Meeting, in Chicago. The study was conducted while Field was at Wake Forest University, in North Carolina.

Field says coffee drinkers don't need to be concerned about his latest discovery: "The brain is pretty remarkable. It can deal with wide ranges of these types of changes."

However, he says researchers need to know about caffeine consumption when they're doing studies. "If you're going to have reliable data, you need to know whether they're coffee drinkers."

He says researchers doing fMRI tests need to control for caffeine consumption, just as they do for other factors.

Dr. S. Ausim Azizi, chairman of the department of neurology at Temple University Hospital and School of Medicine, in Philadelphia, agrees coffee drinkers don't have to pour their java down the drain just yet. Normal blood pressure in the brain has a wide range, and it's natural for blood flow in the organ to vary in response to body changes, he says.

But he agrees that researchers need to account for caffeine use.

"Caffeine could be a confounding factor in functional MRI studies," he says.

What to Do

Azizi says people with normal blood pressure don't need to worry about their morning cup of coffee. However, people with high blood pressure should avoid caffeine.

For more information on caffeine and its effects on health, go to the McKinley Health Center at the University of Illinois, or read this article from Cornell University.

Test your caffeine knowledge with this quiz from InteliHealth.

To learn more about fMRI tests, go to the Massachusetts Institute of Technology.

SOURCES: Interviews with Aaron Field, M.D., Ph.D., assistant professor, radiology, University of Wisconsin, Madison, Wis.; S. Ausim Azizi, M.D., chairman, department of neurology, Temple University Hospital and School of Medicine, Philadelphia; Nov. 28, 2001, presentation, Radiological Society of North America Scientific Assembly and Annual Meeting, Chicago
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