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

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Muscle cells absorb more glucose with creatine

Athletes' muscle cells absorb more glucose if the athletes take creatine. Yet creatine doesn't make muscle tissue more sensitive to insulin, write researchers at the University of Sao Paulo in Amino Acids.

That creatine pumps muscle cells full of glucose is not news. The relationship between glucose balance and creatine supplements is so strong that doctors are considering using creatine as a medicine against diabetes-2. In people who have diabetes-2 the body becomes insensitive to insulin and can no longer manufacture enough of the hormone. As a result, the cells no longer absorb enough glucose.

The researchers wanted to know whether creatine does indeed make muscle cells more sensitive to insulin so they did an experiment with six healthy young men. Half of the men were given a placebo, the other half took creatine for twelve weeks. For the first week the men took 24 g of creatine per day, and for the other eleven weeks they took half the amount.

The men all did training: three times a week they had to run for forty minutes at seventy percent of their VO2max. Just before starting the creatine course and again after four, eight and twelve weeks the researchers gave their test subjects glucose and then measured how quickly the glucose disappeared from the menís blood. The quicker this happens, the quicker the glucose has been absorbed by the muscles.

Muscle cells absorb more glucose with creatine

The figure shows that combination of training and taking creatine does increase the muscle cells' uptake of glucose. But does creatine also affect insulin levels?

To determine whether this was the case, the researchers measured the concentration of insulin in the men's blood first thing in the morning. The researchers had expected that the creatine supplement would increase the production of insulin. But this didn't happen.

Muscle cells absorb more glucose with creatine

They found no statistically significant effect. The muscle cells of creatine users therefore must absorb more glucose through a mechanism that has little to do with insulin. The muscles probably manufacture more of the glucose transport protein GLUT4, the researchers suggest. Other possible factors are an increased production of IGF-1 by the muscle cells, or that muscle cells swell up and as a result absorb more nutrients through osmosis.

The Brazilian research results are yet again proof of the value of creatine supplements for athletes and trainers. For doctors the results indicate that not enough is yet known about the way in which creatine works.

J Nutr. 2008 Nov;138(11):2212-6.