Caffeine, or not caffeine? (Preview)

A recent study raised concerns about caffeine and exercise. What's a coffee lover to do? (non-subscriber preview)


Posted: 2 October 2007
by Judi Ketteler

Wake up, make a beeline for the coffeepot. It's a routine most of us can relate to. In fact, nearly 80 per cent of Brits drink coffee every week. And why not? Coffee stimulates the nervous system, helping us feel more alert, better able to concentrate — not to mention more energised for a five-miler.

On top of that, coffee's high antioxidant content has been attributed to reducing the risk of diabetes, heart disease and Parkinson's disease, and caffeine has been linked to aiding fat metabolism and easing post-workout pain. Some of the 19,000 or so caffeine-based studies carried out over the years indicate benefits for asthma sufferers and Harvard Medical School has stated: "Coffee may reduce the risk of developing gallstones, discourage the development of colon cancer, improve cognitive function, reduce the risk of liver damage in people at high risk for liver disease, and reduce the risk of Parkinson's disease." Quite an endorsement.

Then last year a new study was published that struck fear in the hearts of java junkies everywhere. It suggested caffeine could actually hinder performance, and one of its authors was widely quoted as saying, "Do not drink coffee before doing physical activity." Caffeine might not be as harmless as we thought it was, says Dr Philipp Kaufmann, a professor of cardiology in Switzerland. Here's what all this means for those of us who can't get out the door without a blast of the mean bean.

The adenosine effect

Working at the University Hospital Zurich, Kaufmann and his colleagues found that 200 milligrams of caffeine (about two cups of coffee) decreased blood flow to the heart during exercise by 22 per cent. That percentage increased to 39 for people exercising in a high-altitude chamber, which the researchers used to simulate the way coronary artery disease (CAD, or hardening of the arteries) limits the amount of oxygen that reaches the heart. The effect was not observable at rest.

"When energy is used, a substance called adenosine opens the arteries to facilitate increased blood flow," says Kaufmann. "Caffeine partly blocks the effects of adenosine." Scientists have known about this relationship for quite some time, but the Zurich team was the first to find that the effect was strong enough to measure, and it published its findings in the January 2006 issue of Journal of the American College of Cardiology.

Since an increase in blood to the heart is necessary for aerobic activity, the findings, theoretically, suggest caffeine could slow you down by some measure. The study's purpose, however, wasn't to look at whether caffeine could help athletes go faster or farther. Instead, it set out to investigate the effect caffeine has on blood flow to the heart. "Patients with CAD usually have decreased blood flow reserve already," says Kaufmann. "A further decrease could, in theory, be a problem for them." Furthermore, their findings suggest to Kaufmann that reduced blood flow "cannot be considered favourable" during exercise for anyone, including runners.

Grounds for coffee consumption

As frequently happens with nutrition news, the pendulum then swung back in caffeine's favour. An April 2006 Journal of Sports Science study found caffeine had a positive impact on the performance of male distance runners. A group of caffeine drinkers, who downed 1.4mg of caffeine per pound of body weight (a 355ml coffee for a 68kg person), had a 1.2 per cent improvement in an 8K race.

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