Caffeine: No boost for one in 10 of us

I’ve often wondered why I don’t get a lift from strong coffee. Now I know. An espresso is supposed to boost energy levels, but for around one in 10 people it may have the opposite effect.

A while back, scientists discovered that variations in a specific gene control the way the body metabolises coffee. People with two copies of this variant (about 50% of us) are “fast” metabolisers: coffee gives them a jolt, and then it’s gone.

Some 40% have one copy and are “moderate” metabolisers. The rest are “slow” metabolisers. This means the drug lingers longer in the body – not good.

In 2006, researchers from Toronto University found that slow metabolisers who drink a lot of coffee are more likely to have heart attacks than faster metabolisers. Now they’ve found that caffeine also saps their energy levels.

For their study, the team recruited 100 male athletes and tested their DNA to determine how fast they metabolise coffee. They then gave them either a dose of caffeine or a placebo, and asked them to cycle 10km as fast as possible.

Fast metabolisers completed the course 7% faster, on average, after ingesting caffeine than after the placebo. The moderate metabolisers performed about the same while the slow metabolisers were 14% slower.

The researchers speculate that when caffeine stays in the body, it narrows the blood vessels, restricting the flow of blood and oxygen to tiring muscles.