April 26, 2007
Among older adults, the extended bed rest that sometimes accompanies a hospital visit can contribute to substantial muscle deterioration, according to new data from the University of Arkansas (http://www.uams.edu).
“We found a dramatic reduction in muscle protein synthesis brought on by inactivity that caused the muscle loss,” said William J Evans, PhD, director of the Nutrition, Metabolism and Exercise Laboratory in the Donald W. Reynolds Institute on Aging at UAMS.
“This is a striking loss of muscle in healthy individuals. When you consider the chronically ill facing longer hospitalizations or bed rest, the magnitude of muscle loss is extraordinary and should be treated," Evans added.
Evans was part of the team of researchers at the University of Arkansas for Medical Sciences who contributed to a report that showcased the findings in the April 25 issue of the Journal of the American Medical Association.
Data in the report found the rate of muscle loss in 12 adults with an average age of 67 over 10 days was more remarkable and in a shorter period than a previous study of younger adults.
The researchers attributed the increased muscle tissue loss to inactivity that results in a large decrease in the ability of muscle cells to make new protein, the primary constituent of muscle.
Evans said the study, “The Effect of 10 Days of Bed Rest on Skeletal Muscle in Healthy Older Adults,” demonstrated the “best case scenario,” as the subjects were healthy with no functional limitations. Older patients hospitalized with disease or trauma could also face other factors such as inflammation and decreased food intake that could contribute to further loss of muscle tissue and function, he said.
Evans said continued research by the team will examine different strategies for preventing muscle loss. Those potential treatments included nutritional supplements, exercise and the use of insulin sensitizers to prevent the reduction in muscle protein synthesis.
According to the study, there was a 30 percent decrease in the rate of protein synthesis in muscle cells between the measurements taken before and after the 10 days of bed rest. Evans said the researchers also found the bed rest likely caused an increase in insulin resistance, which he said further ratcheted down the protein synthesis rate.
Evans noted that the older adult participants in the UAMS study experienced more muscle loss in 10 days than did younger participants after 28 days as reported in a 2004 article in the Journal of Clinical Endocrinology Metabolism. In that study, an average loss of less than 0.4 kg in leg lean mass was reported after 28 days bed rest in subjects with an average age of 38.
The muscle loss study appeared in a research letter published in the journal and is available online at http://jama.ama-assn.org/. The Journal of the American Medical Association, published continuously since 1883, is the most widely circulated medical journal in the world.