Researchers at the University of Colorado Anschutz announced on June 29 that healthy but sedentary adults display a significant, coordinated decline in muscle mitochondrial function, which may precede the onset of major diseases such as cancer, diabetes, and Alzheimer's.
"Mitochondrial function is the center of metabolic health," said Iñigo San Millan, adjoint assistant professor in the Division of Endocrinology, Metabolism and Diabetes at CU Anschutz and senior author of the study. "If you are 40, healthy, and sedentary, it is likely that you already have something going on inside your cells that will likely come back to haunt you in 10 or 15 years."
The study found that mitochondria—cellular structures responsible for processing energy—had a significantly reduced ability to burn both sugar and fat in healthy individuals who exercised less than the recommended 150 minutes per week. Sedentary muscle was also found to contain about half as much MPC1 protein as active muscle; this protein plays a key role in transporting sugar breakdown byproducts into mitochondria for energy conversion.
Published in Clinical Bioenergetics, the research examined nine sedentary men and ten regularly active men with an average age of approximately 42 years old. Muscle biopsies were analyzed to assess how efficiently mitochondria burned fuel. Exercise tests measured fitness levels, fat-burning capacity, and blood lactate—a marker indicating how hard the body works for energy.
San Millan said these findings indicate a fundamental shift in cellular identity among sedentary people: "Sedentary people aren't just 'out of shape'—their cells are losing the ability to process fuel efficiently." He explained that a sharp drop in MPC1 could be an early sign leading toward insulin resistance and type 2 diabetes.
The research team plans larger trials with more diverse participants and intends to test whether interventions such as exercise or medication can restore MPC1 levels. "This cellular decline is something we can actually test for in a non-invasive way," San Millan said. "And if we catch it early, we can prescribe targeted exercise programs designed to restore mitochondrial health and potentially prevent future disease."
