By Daniel Schneider
We know that type 2 diabetes is characterized by decreased insulin sensitivity, that is, the body is less responsive to the insulin it produces. But less well known is that those with type 1 diabetes also exhibit decreased insulin sensitivity, or insulin resistance. It is theorized that this insulin resistance is a player in the complications faces by those with both type 1 and type 2 diabetes. As such, this article applies to all of us.
We feel pretty confident when we say that exercise is good for people. And that probably rings especially true for those of us with diabetes. This article sought to examine a novel means by which exercise helps improve insulin sensitivity, or lower insulin resistance. We know that exercise improves insulin sensitivity in the short term, and the author’s note many reasons for this. Things like increased levels of GLUT-4 (a glucose transporter that brings glucose into the cell) and increased glycogen synthase (an enzyme that helps store glucose as glycogen) are both known to be responsible for improved insulin sensitivity after exercise. However, these improvements go away after a few days of not exercising, and the authors wanted to know what might account for long term improvements in insulin sensitivity in those people who exercise.
Capillaries are the tiny blood vessels that deliver oxygen, nutrients, and hormones to all of the cells and tissues of the body. When we exercise, our body adapts to be able to deliver nutrients more effectively, and one of the ways it does that is by increasing capillary density. If more capillaries are serving muscle tissue, that muscle should be better able to use more of the oxygen, glucose, and insulin delivered to it.
The authors had subjects in the study train on a treadmill at 75% of their heart rate reserve, 45 minutes, 3 times per week for 6 months. This probably equates to a fairly quick jogging pace for a healthy individual. Then the author’s had the subjects “detrain” or rest for 2 weeks. This 2 week period was enough time for Glut 4, Glycogen synthase, and other markers of short-term exercise to return to normal levels. However, capillary density remained elevated after this period without exercise. And, the capillary density of the subjects closely matched the improvements in insulin sensitivity, leading the authors to believe that capillary density is an important player in insulin sensitivity.
As we discussed, exercising is the best known way to improve capillary density. And as the study suggests, improved capillary density will stick around for awhile after exercising, perhaps supporting long-term insulin sensitivity.
All the more reason to get out and run/bike/swim/hike/do some yoga, or whatever else makes you happy!