Issue 156 Item 8 Cell Changes May Explain Diabetes Risk in Elderly

Diabetes may become more common with age because of a decline in the function of mitochondria, the powerhouses of the body’s cells. The good news, they say, is that exercise might counter this decline.

In a study that compared 13 healthy people ages 18 to 39 with 16 healthy people ages 61 to 84, the elderly participants were found to have greater insulin resistance, which is a precursor to type 2 diabetes.

However, the difference was not due to higher body fat among the older participants, who were just as lean as their younger counterparts.

Insulin is a hormone produced by the pancreas that allows blood sugar, or glucose, to enter cells so it can be used as energy. Mitochondria, found in a cell’s cytoplasm, are responsible for converting glucose and fatty acids into energy.

This process is impaired during insulin resistance, when the body becomes less sensitive to the effects of insulin, prompting the pancreas to pump out more insulin to try to compensate. A big question has been why older adults have high rates insulin resistance and full-blown type 2 diabetes. Type 2 diabetes affects about one in four people older than 60, noted study author Gerald I. Shulman of the Howard Hughes Medical Institute at Yale University in New Haven, Connecticut.

In the new study, reported in the May 16th issue of Science, Shulman and colleagues showed that the metabolic activity of the mitochondria in muscle cells was about 40 percent lower in the older participants.

They also showed more fat accumulation in their muscle and liver tissue, assessed through non-invasive scans. “This finding is important because studies in our lab and others have shown that the amount of lipid (fat) inside the muscle cell is a very good predictor of insulin resistance,” Shulman said in a statement.

The results suggest that fat builds up in the muscle of older people because of the decreased activity of the cells’ fat-burning mitochondria, according to the researchers.

“These data support the hypothesis that an age-associated decline in mitochondrial function contributes to insulin resistance in the elderly,” they conclude in the report.

On a positive note, exercise may help counter this process, because research has shown that physical activity increases mitochondria in muscle by activating an enzyme known as AMP kinase, Shulman explained in the statement. “This is yet another reason for seniors to maintain an active lifestyle,” he said.

SOURCE: Science 2003;300:1140-1142.

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FACT: Nearly one in 10 Latinos age 40 or older has a potentially sight-robbing condition that is related to diabetes. That, according to a California survey released this week. However, nearly 30 percent of those surveyed were unaware they had diabetes, much less a complication that can damage sight. “That is a huge number of undiagnosed cases of diabetes,” said Dr. Rohit Varma, an associate professor of ophthalmology at the University of Southern California in Los Angeles. Los Angeles Latino Eye Study