It has been thought, assumed, or passed on as fact that coffee causes dehydration. This belief is based on the fact that it contains caffeine—a very mild diuretic. As of a few days ago, however, this age old “fact” has been overturned. Coffee doesn’t in fact dehydrate us.
Sophie Keller, a sports scientist, wanted to study coffee’s effects on fluid balance. Considering the fact that everyday nearly 1.6 billion cups of coffee are drunk, Keller believed that a modern reassessment of coffee’s role in hydration was needed.
In a relatively straightforward experiment, Keller asked 50 healthy men to drink either 4 mugs of water or coffee a day for three days and then switch. Methods of control included having the participants maintain the same diet, as well as abstaining from exercise or alcohol.
At the end of the experiment , blood and urine tests showed the men were just as well hydrated when they drank coffee as when they had water. In addition, they all passed the same amount of urine. So does this overturn the long running theory that coffee dehydrates?
Keller thinks it does. Others are still skeptical about coffee’s contribution to hydration. Keller does concede that coffee doesn’t lead to dehydration…when consumed in moderate amounts. Physicians like Dr Frankie Phillips of the British Dietetic Association believe that a small, strong coffee such as an espresso may dehydrate.
In general, however, caffeine’s diuretic effects is more or less neutralized. This is because the caffeine in the drink is balanced by the water content. Therefore, hydration rather than dehydration occurs.
So where does the original idea—that coffee dehydrates—come from? It seems that back in 1928 a scientific study was conducted on caffeine. This study reported caffeine’s diuretic effects, but didn’t take into account the beverage’s water content acting as a balance. To this day, even the minor diuretic effects of caffeine are not well understood.
We’re not saying that you should take a bottle of coffee when you go a long run. But we’re also not saying that for every cup of coffee you must ingest a cup of water. That said, hydration is something that should be taken very seriously, especially if you exercise regularly. Acute dehydration is one of the scarier things to go through in life.
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