Scientists at Joslin Diabetes Center scientists now have discovered that some benefits of aerobic exercise may be dampened by hyperglycemia.
Hyperglycemia is a medical condition in which people have higher-than-normal blood sugar levels.
These diminished gains are seen in mouse models and humans with chronic hyperglycemia that is in the “prediabetes” range.
The study which also showed that this maladaptive trait is independent of obesity and insulin levels in the blood, has been published in Nature Metabolism.
Clinical studies have demonstrated that people with diabetes or chronically high levels of blood sugar struggle to improve their aerobic exercise capacity compared to people with normal blood sugar levels.
The idea behind this study was to see if high blood sugar in mice could impair their ability to improve their aerobic fitness.
The study also aimed to uncover the mechanisms that may lead to low fitness levels in people with hyperglycemia.
Two major causes of Hyperglycemia
Two major causes of hyperglycemia in humans, discovered by the study are:
One group of mice consumed a Western diet, high in sugar and saturated fat, which caused some weight gain in addition to hyperglycemia.
The other group was modified to produce less insulin, which caused similar increases in blood sugar as the Western diet, even though the mice ate a diet lower in sugar and fat, and maintained normal body weight.
Both groups were subjected to a training protocol in which they ran in wheels in their cages to boost their aerobic fitness.
In both hyperglycemic groups, animals ran around 500 kilometers over the course of the study but, on average, failed to improve their aerobic exercise capacity compared to mice with lower blood sugar levels, Lessard says.
Looking in more detail at skeletal muscle in these mice, scientists saw that the muscle was not adapting to the aerobic challenge as muscle normally would.
Muscle tissue can remodel itself, which is one reason why exercise becomes easier when we do it regularly. Over time, aerobic exercise such as running or swimming can alter muscle fibers to become more efficient at using oxygen during exercise.
The scientists propose that high levels of blood sugar may prevent muscle remodeling in part by modifying the “extracellular matrix” proteins in the space between the muscle cells, where blood vessels are formed.
Following up on these animal findings in clinical tests with young adult volunteers, the Joslin scientists found that those who had higher blood sugar levels in response to ingesting glucose, a condition known as impaired glucose tolerance, showed the lowest aerobic exercise capacity.
Overall, the study suggests several approaches that might help people with chronic hyperglycemia eventually overcome the obstacles to building aerobic capacity. One is to adopt a diet designed to keep blood sugar levels low. Another is to take existing diabetes drugs designed to keep blood sugar levels in normal ranges.
