Originally published February 23 2006
Zurich researchers determine that caffeine affects blood flow to the heart
by Mike Adams, the Health Ranger, NaturalNews Editor
New research conducted at the University Hospital in Zurich suggests that caffeine restricts blood flow to the heart during exercise.
Blood flow to the heart has to increase during exercise in order to match the increased need of oxygen.
But when 18 healthy people were given the equivalent of two cups of coffee, scientists found that blood flow increase during exercise was much lower than when they exercised without having consumed coffee.
This effect was even stronger when the participants were in a chamber simulating high altitude, said the scientists at the University Hospital in Zurich.
They say that although caffeine drinks are known to stimulate the brain, their results show that caffeine is unlikely to boost athletic performance.
A UK team previously reported that introducing caffeine into sports drinks increased the rate in which carbohydrate is delivered to the athlete.
The caffeine dose did not affect blood flow within the heart muscle while the participants were at rest.
However, the blood flow measurements taken immediately after exercise were significantly lower when the participants had taken caffeine tablets.
The ratio of exercise blood flow to resting blood flow, called the myocardial flow reserve, was 22 per cent lower in the group at normal air pressure after ingesting caffeine.
Author Dr Philipp Kaufmann said that caffeine may block certain receptors in the walls of blood vessels, interfering with the normal process by which adenosine signals blood vessels to dilate in response to the demands of physical activity.
It may be a stimulant at the cerebral level in terms of being more awake and alert, which may subjectively give the feeling of having better physical performance.
Dr Kaufmann added that the study was not designed to measure athletic performance but even though it was small, the differences were large enough for the team to be confident that the effect of caffeine on heart muscle blood flow is real.
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