A recent study last year raised concerns about caffeine and exercise. What's a coffee lover to do?

Wake up, make a beeline for the coffeepot. It's a routine most of us can relate to. In fact, over 70 per cent of Australians drink coffee every week. And why not? Coffee has been linked to numerous health benefits such as reduced risk of diabetes and heart disease, aided fat metabolism, eased post-workout pain, not to mention it stimulates the nervous system, helping us feel more alert and energised for a 10K.

Then in 2006 a new study 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, 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
Kaufmann and his colleagues at the University Hospital Zurich found that 200ml 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."

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. 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 0.56mg of caffeine per kilogram of body weight (a 355ml coffee for a 68kg person), had a 1.2 per cent improvement in an 8K race.