Dr's Casebook: Exercise affects your metabolism and builds bone

Dr Keith Souter writes: Exercise seems to stimulate a hormone called ‘irisin.’ It is named after Iris, the Greek messenger goddess, because it seems to deliver a message from the muscles that stimulates these amazing changes in the body.

Scientists found the hormone in the membranes of muscles cells when they were investigating a particular gene that seems to be switched on by exercise. Having found the hormone, they used lab cultures and mice to show that irisin has a powerful effect on white adipose tissue. This is the type of fat that accumulates under the skin and contributes to obesity. The irisin causes the body to convert white fat to brown fat. Brown fat is regarded as ‘good’ fat, because it burns off more calories than exercise alone.

In the mice studies the researchers found that not only was white fat converted into brown fat, but also it had a positive effect on glucose tolerance. This could be of vital importance as a treatment in the future, since the link between white fat and obesity and diabetes is well known.

Exercise has long been promoted to build bone mass, although exactly how it does so has not been known. Further work with mice shows that the role of irisin is critical. It activates a protein called sclerostin, which is important in bone remodelling. Bone remodelling is the name for the continual process of resorption of old bone and the formation of new bone to maintain bone mass. Osteoporosis or thinning of the bones occurs when there is too much resorption and not a corresponding amount of new formation to balance it.

In this research mice were given doses of irisin for six days. This resulted in raised levels of sclerostin and significantly boosted their bone mass. The exact pathways that irisin is involved in have yet to be determined, but it may open up new targets for treatment of osteoporosis in the future. All in all, it reaffirms the profound benefits of exercise, because exercise releases irisin.