Caffeine curbs heart’s blood flow during exercise
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Drinking two cups of caffeinated coffee decreases blood flow to the heart during exercise, researchers report, and the reduction may be most pronounced at high altitudes. While healthy people may tolerate the reduced blood flow fairly easily, it may be harmful to people with coronary artery disease.
Dr. Philipp A. Kaufmann and colleagues from University Hospital Zurich, examined the immediate effects of caffeine on blood flow to the heart at rest and after exercise in healthy young adult volunteers exercising at normal oxygen levels or simulated low-oxygen levels that occurs at high altitudes.
The team measured cardiac blood flow at baseline and 50 minutes after ingestion of 200 mg caffeine, equivalent to about two cups of coffee.
They report that caffeine did not alter resting myocardial blood flow at normal oxygen levels. At low-oxygen levels, resting myocardial blood flow was significantly increased by caffeine.
During exercise, a significant decrease in blood flow to the heart was observed at normal oxygen levels and at low-oxygen levels.
Caffeine led to a 22 percent drop off in so-called “myocardial flow reserve” at normal oxygen levels and a 39 percent decrease at low-oxygen levels.
These findings, the authors conclude, support that exercise-induced blood flow response may at least in part be antagonized by caffeine.
SOURCE: Journal of the American College of Cardiology, January 17, 2006.
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