Exercise can act like insulin to help treat people with diabetes, accordingto new research from the University of Limerick. Patricia Weston reports
Researchers at the University of Limerick have discovered that when you exercise, your body produces substances that act like insulin. The findings represent great news for diabetes sufferers who can benefit from incorporating exercise into their standard diabetes treatments.
Every one of us carries about 450g of sugar in the form of glucose in our muscles - equivalent to half a bag of sugar. The glucose provides energy to power muscles, but diabetics are deficient in this respect as their bodies either don't produce sufficient insulin, or can't use existing insulin properly to utilise energy-giving glucose.
Muscles carry most of the glucose and hold more than the liver, according to Prof Philip Jakeman, professor of exercise science at the University of Limerick who heads the research. "Muscle is the major repository for glucose in the body. Exercise can increase the rate of glucose uptake into muscle independent of insulin. Exercise therefore has an insulin-like effect."
Diabetes is a disease in which the body can't properly regulate sugar levels in the blood. Sugar uptake into the muscles is controlled by insulin, with the body balancing between having too much and too little glucose in the bloodstream through the release of insulin. There are two main types of diabetes, Type I where the person doesn't produce any insulin and must take daily injections, and Type II where the person may produce insulin but can't make effective use of it.
Type II diabetics do not respond to insulin in the peripheral areas of the body in particular, which are the muscles and adipose or fat tissue. As almost half the body weight is made up of muscle there is great potential to increase glucose uptake into muscle and get it out of the bloodstream by exercising, says Jakeman. "Insulin is the major hormone linked with peripheral glucose uptake. Insulin stimulates the uptake of glucose into skeletal muscle and other tissues. Exercise - muscle contractility - achieves the same effect."
THE UL researchers studied this by observing non-diabetics during exercise. They took biopsy samples from the muscles during and after exercise, and also took blood samples from the veins. It was found that single bouts of exercise stimulate glucose uptake for between 24 and 72 hours afterwards, and regular training leads to more permanent adaptation of the muscle tissues. Jakeman recommends exercise and training as a booster therapy for those with Peripheral Insulin Resistance.
In non-diabetics insulin passes via the bloodstream to the peripheral tissues and attaches itself to a cell surface receptor that activates a response inside the cell. In order for the cell to take up glucose, insulin has to trigger a protein receptor known as GLUT. An increase in GLUT means an increase in glucose uptake to the cells, explains Jakeman.
People who suffer from diabetes have a defect in their insulin receptor and/or a defect in the signalling pathway that results in fewer GLUT receptors and thus less glucose uptake in the cells. Exercise increases the amount of GLUT receptors.
As well as increasing glucose uptake, Jakeman's research found that exercise also releases the activity of IGFs, Insulin-like Growth Factors. "It acts like insulin, and 85 per cent of it is the same as insulin," says Jakeman. "It is held in the circulatory system even when the insulin is all used up. These IGFs are associated with a binding protein, which allows them to stay in the circulation for longer. The binding protein's potency is greater than insulin." The findings are important for yet another reason. Obesity is becoming a health crisis in this country and greatly increases a person's risk of developing Type II diabetes, says Jakeman. Exercise therefore helps in two ways: by stimulating the uptake of glucose from the bloodstream in diabetics, but also providing valuable aerobic exercise to those who may be overweight.
Jakeman's ongoing research, funded by the Wellcome Trust and Enterprise Ireland, was prompted by the startling increase of obesity in America. "In the US one sixth of the whole country is physically unfit. Health care costs are therefore 30 per cent less for the fit than for the unfit." He believes that Irish people could save significantly on health care costs if we were fitter.