Coffee and workouts

are considered to be moderate metabolisers, whereas people with two copies of the slowmetabolising variant are, of course, slow caffeine metabolisers.

About 40% of us are thought to be moderate metabolisers, with the remaining 10% being genetically slow metabolisers.

In 2016, el-sohemy and his colleagues published a study in JAMA showing that slow metabolisers had a heightened risk of heart attacks if they frequently drank coffee, compared to people who were genetically classified as fast caffeine metabolisers. The scientists theorised that the drug, which can constrict blood vessels, hung around and produced longer-lasting – and in this case undesirable – cardiac effects among the slow metabolisers.

But few large experiments had focused on how people’s CYP1A2 genetic profile might influence their athletic performance after swallowing caffeine.

So for the new study, which was published this month in Medicine & Science in Sports & Exercise, el-sohemy, together with his graduate student Nanci Guest and other colleagues, decided to ply about 100 willing, young, male athletes with various doses of the drug.

The scientists swabbed the men’s cheeks, analysed their CYP1A2 genes and, based on which variants each man carried, categorised them as fast, moderate or slow caffeine metabolisers.

Then they had the athletes complete three separate sessions of pedalling a stationary bicycle for 10 kilometres as quickly as possible. Before one ride, the men received a low dose of caffeine (2 milligrams for every kilogram of their body weight, or about the amount found in one large cup of coffee). Before another, they swallowed twice as much caffeine; and before a third, a placebo.

Their subsequent time trial results showed that, on aggregate, the men performed better with caffeine, especially after the higher amount.

But there were substantial differences by gene type.

The fast metabolisers rode nearly 7% faster after they had downed the larger dose of caffeine compared to the placebo. The moderate metabolisers, by contrast, performed almost exactly the same whether they had received caffeine or a placebo.

It was the slow metabolisers, however, who showed the greatest impact, although in a negative direction. They completed the 10 kilometre ride about 14% more slowly after the higher dose of caffeine than after the placebo.

Just how caffeine differentially boosted or blunted the men’s athletic performance remains unclear.

But el-sohemy suspects that, as in the heart-attack study, caffeine lingered in the slow metabolisers, narrowing their blood vessels and reducing the flow of blood and oxygen to tiring muscles.

In fast metabolisers, the drug likely provided a quick gush of energy and then was cleared from their bodies “before it could do the bad stuff”, he says.

This study involved only healthy young men and bicycling. It cannot tell us whether caffeine likewise gooses or inhibits performance for other people in other sports.

And it cannot answer the broader question of whether we need a genetic test before deciding if we should mainline coffee in advance of our next workout.

Physical performance involves, after all, so many factors, including motivation, sleep, stress, overall nutrition, and the working of a vast number of genes, many still be unidentified.

So if you find that coffee seems to impede your performance, you could use a genetic test to characterise your CYP1A2 gene and confirm that you are a slow metaboliser. Or you could not drink coffee before you exercise. – The New York Times