Caffeine, diuretic? Does it cause dehydration?

The study found that caffeinated drinks retain water in the same way as water or sports drinks. (Maria/Unsplash)

Caffeine has long been said to be a diuretic. For some people, this is tantamount to advice: people at risk of dehydration, or in extremely hot weather, do not drink caffeinated drinks. This proposal may be well-intentioned, but it is wrong.

By definition, diuretics increase urination, so water or any beverage is a diuretic when consumed in large quantities. Importantly, excessive urination does not necessarily lead to dehydration.

Drinking water not only rehydrates the body (to prevent dehydration), but also promotes urination. Caffeine is a weak diuretic. If you don't take too much caffeine, the body can quickly gain tolerance and avoid chronic dehydration.

In fact, humans have known this for nearly a hundred years! A 1928 study showed that the intake of half a milligram of caffeine per kilogram of body weight (half a cup of coffee) led to a significant increase in urine output when the three participants did not eat caffeine for the first two months. But four or five days later, the human body gained tolerance.

More than a decade ago, this discovery was supported by contemporary research methods and analytical surveys. The study monitored 59 people for 11 days. In the first six days, all people consumed 3 milligrams of caffeine per kilogram of body weight (2 to 3 cups of coffee a day), and in the next 5 days, they were divided into three groups with zero, low (1 cup) and medium (2 cup) levels of caffeine, respectively.

Caffeine has little effect on hydration. (Annie Spratt/Unsplash)

The researchers monitored a variety of indicators of hydration, including urine volume and color, and found that none of them was affected by regular caffeine intake.

Recently, the "hydration academic" put forward the index of "Beverage Water and Index" (beverage hydration index) to describe the ability of different beverages to retain water in the human body; once again, the general intake of caffeine (such as coffee, tea or cola) is similar to the water retention capacity of water or other sports drinks.

One advantage of the index is that it acknowledges that all drinks rehydrate the body (some of which are more effective). If people are advised not to drink their favorite drinks (simply because they contain caffeine), people may not automatically change drinks, resulting in a reduction in total water intake.

There is solid evidence that lack of water affects health (especially for the weak), interferes with mood, brain and heart function, and leads to a poor prognosis of hospitalized elderly patients.

So while some caffeinated drinks (such as cola and energy drinks) have their own problems, such as high sugar content, from a fluid balance point of view, you don't have to worry about caffeine.

Ben Desbrow is an associate professor of sports nutrition and dietetics at Griffith University University in Brisbane, Australia. He has invented hydration beer. This article was originally published on the website The Conversation. The translation is slightly abridged.