Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Why energy drinks contain glucuronolactone

If you ask an average nutritionist why energy drinks contain glucuronolactone [structural formula on the right], she'll probably sigh in a scientific way, shrug her shoulders and tell you that glucuronolactone is 'nonsense'.

"Not effective"
"Energy drinks contain caffeine, and that has a slight stimulatory effect", she's likely to say. "But as far as the other things that manufacturers put in those cans go, none have ever been proved to be effective. Glucuronolactone is only in there to give consumers the idea that they've purchased something special." And that'll be the end of the conversation.

Why energy drinks contain glucuronolactone

But your average nutritionist tends to pooh-pooh everything we think is interesting, so we continue undeterred. When we discovered supplements being sold in an online store in which glucuronolactone was the only active ingredient we went in search of more information on the substance. And that's how we found the animal study that Shunkichi Tamura published in the 1960s in the Japanese Journal of Pharmacology.

Glucuronolactone is a substance that is produced when glucose is converted in the liver.

In the 1960s physiologists did a lot of research on glucuronolactone. They discovered for example that during long-term and intensive exercise all sorts of toxic waste products start to circulate through the body, which in ex-vivo studies had shown that they could stop the heart of lab animals from beating. If you administer glucuronolactone, then this doesn't happen or happens less quickly.

The Japanese started to wonder whether glucuronolactone might have performance-enhancing properties. They injected glucuronolactone, and also glucose, glycogen and a number of other related compounds, in a dose of 100 mg per kg bodyweight directly into the gut of lab rats, waited 30 minutes and then got the rats to swim to the point of exhaustion.

The human equivalent of the dose would be between 1 and 2 g. A can of Red Bull contains 600 mg glucuronolactone.

Immediately afterwards the Japanese repeated the procedure twice. During the second and third sessions, glucuronolactone extended the amount of time that the animals were able to swim by more than the other substances that were tested.

The amount of time that the rats were able to swim for in their first session is fixed at 100 percent in the figure below.

Why energy drinks contain glucuronolactone

The researchers refrain from making any claims about the way in which glucuronolactone might improve performance. One obvious possibility is that glucuronolactone boosts detoxification or glucuronidation for the scientifically minded.

Why energy drinks contain glucuronolactone

Another study
In another publication, which we have not been able to track down, the Japanese compared the performance-enhancing effect of glucuronolactone with that of stimulants such as caffeine and amphetamines in a similar way as described above.

During that experiment they discovered that stimulants only improved endurance capacity during the first session of physical exertion, while glucuronolactone only had an effect during the second and third sessions. In a study published in 1966 [Jpn J Pharmacol. 1966 Jun;16(2):138-56.] they describe these experiments in a few sentences.

Why energy drinks contain glucuronolactone

So it would seem that the effects of caffeine and glucuronolactone complement each other. The people who dreamed up the composition of Red Bull apparently knew what they were up to.

Jpn J Pharmacol. 1968 Mar;18(1):30-8.

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