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article imageStudy finds insulin boost restores muscle growth in elderly

By Bob Ewing     Sep 27, 2009 in Science
University of Texas Medical Branch at Galveston (UTMB) researchers found increased insulin levels in elderly test subjects, can restore the impaired muscle-building process responsible for age-related physical weakness.
Insulin use is most commonly associated with diabetes; however, this hormone does have another purpose. Insulin is also essential for muscle growth as it increases blood flow through muscle tissue. This increased flow encourages nutrients to disperse from blood vessels and is a biochemical signal to boost muscle protein synthesis and cell proliferation.
UTMB researchers have recently found when insulin levels are increased above the normal range in elderly test subjects, the impaired muscle-building process responsible for age-related physical weakness can be restored.
The UTMB blog quotes Dr. Elena Volpi, senior author of a paper on the study published in the September issue of Diabetologia as saying “Insulin is normally secreted during food intake. When you give insulin intravenously and increase the blood insulin levels to the same amount produced after a meal, you see that in young people it stimulates protein synthesis and muscle growth, while in older people it really doesn’t. But when we gave seniors double the insulin they would normally produce after eating, their muscles were stimulated like those of young people.”
Volpi, working with postdoctoral fellows Satoshi Fujita and Kyle Timmerman, graduate student Erin Glynn and Professor Blake B. Rasmussen, examined the response of thigh muscle to the two different blood insulin levels of 14 elderly volunteers.
The data showed a blood insulin level double that produced by a typical meal seems to turn back the clock on elderly thigh muscle.
“While we had called this ‘insulin resistance’ in the past, we didn’t really have evidence that you can get an elderly person’s muscle to grow if you give it a lot more insulin, which is what we needed to truly say this is insulin resistance,” Volpi said.
She added, “These were older subjects with perfect glucose tolerance,” she said. “So what we have identified is a novel kind of insulin resistance that’s not related to sugar control.”
The team is currently testing if using drugs to dilate muscle blood vessels during insulin exposure can improve muscle growth in older people.
“Preliminary data suggest that this treatment may be effective, but these data are not yet published,” Volpi said.
“On the other hand, in a paper we published two years ago in Diabetes, we showed that a single bout of aerobic exercise — a staple of diabetes treatment — may also improve muscle growth in response to insulin in older nondiabetic people.”
The researchers are undertaking a larger, NIH-funded clinical trial to determine if aerobic exercise and nutritional supplementation for six months can also boost muscle size and function in sedentary but otherwise healthy seniors.
More about Muscle growth, Elderly, Insulin
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