Exercise helps flow of mysterious hormone in your blood

An exercise-induced hormone does exists in humans, say scientists, adding that this hormone, called irisin, circulates in the blood at nanogram levels and increases during exercise.

Irisin's discovery in 2012 was exciting because scientists had potentially found one reason why exercise keeps us healthy.

When irisin levels were increased in mice, their blood and metabolism improved.

But the presence of Irisin in humans was recently questioned by groups of scientists.

In new research, the authors show that human irisin is similar to the mouse hormone and that it circulates in the range previously reported.

Although irisin circulates at low levels (nanograms), this range is comparable to that observed for other important biological hormones such as insulin.

According to senior study author Bruce Spiegelman from Dana-Farber Cancer Institute and Harvard Medical School, that the confusion over irisin comes down to disagreement over how irisin protein is made in skeletal muscle cells and the detection limits of protocols.

He and co-author Steven Gygi turned to state-of-the-art techniques to show that the human hormone uses a rare signal ATA (start codon) to initiate the production of irisin.

Furthermore, the investigators developed a protocol, that does not rely on antibodies, to precisely measure how much irisin increases in people after exercise.

"The data is compelling and clearly demonstrates the existence of irisin in blood circulation," said endocrinologist Francesco Celi from the Virginia Commonwealth University's medical center, who was not involved with the study.

"Importantly, the authors provide a precise and reproducible protocol to measure irisin," he added.

Further studies are necessary to fully understand how the hormone works in humans, specifically how it relates to brown and beige fat tissue and energy use, the authors noted in a paper detailed in the journal Cell Metabolism.

Results from human studies are still mixed as to what kinds of exercise raise irisin, but data suggest that high-intensity training protocols are particularly effective.