In studies of young and elderly people, the researchers found that older people had lower levels of metabolic activity in their mitochondria, the "factories" that provide power to cells. The findings suggest that reduced mitochondrial activity underlies insulin resistance, which is a major contributor to type 2 diabetes in the elderly.
In another recent study the researchers also found that physical activity can enhance the number of mitochondria in muscle by activation of a key enzyme called AMP kinase. "This is yet another reason for seniors to maintain an active lifestyle," said the study's senior author, Gerald Shulman of the Howard Hughes Medical Institute at Yale. Shulman and his colleagues reported their findings in the May 16, 2003, issue of the journal Science.
According to Shulman, pinpointing the cause of type 2 diabetes in the elderly would help solve a major health problem. "Approximately one in four individuals over the age of 60 has type 2 diabetes, which is a remarkable statistic," said Shulman. "And, if you add impaired glucose tolerance, you're talking about forty percent of the population."
The estimated economic burden of diabetes in United States is about $100 billion per year, a substantial proportion of which is due to diabetes in the elderly, said the researchers.
At the biochemical level, the hormone insulin promotes the transfer of glucose in the blood into cells for energy production and storage. Mitochondria within the cells convert glucose and fatty acids into energy via oxidation.